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super-earths - planets with sizes between the earth and neptune - are found in tighter orbits than that of the earth around more than one third of main sequence stars. it has been proposed that super-earths are scaled-up terrestrial planets that also formed similarly, through mutual accretion of planetary embryos, but in discs much denser than the solar protoplanetary disc. we argue instead that terrestrial planets and super-earths have two clearly distinct formation pathways that are regulated by the pebble reservoir of the disc. through numerical integrations, which combine pebble accretion and n-body gravity between embryos, we show that a difference of a factor of two in the pebble mass flux is enough to change the evolution from the terrestrial to the super-earth growth mode. if the pebble mass flux is small, then the initial embryos within the ice line grow slowly and do not migrate substantially, resulting in a widely spaced population of approximately mars-mass embryos when the gas disc dissipates. subsequently, without gas being present, the embryos become unstable due to mutual gravitational interactions and a small number of terrestrial planets are formed by mutual collisions. the final terrestrial planets are at most five earth masses. instead, if the pebble mass flux is high, then the initial embryos within the ice line rapidly become sufficiently massive to migrate through the gas disc. embryos concentrate at the inner edge of the disc and growth accelerates through mutual merging. this leads to the formation of a system of closely spaced super-earths in the five to twenty earth-mass range, bounded by the pebble isolation mass. generally, instabilities of these super-earth systems after the disappearance of the gas disc trigger additional merging events and dislodge the system from resonant chains. therefore, the key difference between the two growth modes is whether embryos grow fast enough to undergo significant migration. the terrestrial growth mode produces small rocky planets on wider orbits like those in the solar system whereas the super-earth growth mode produces planets in short-period orbits inside 1 au, with masses larger than the earth that should be surrounded by a primordial h/he atmosphere, unless subsequently lost by stellar irradiation. the pebble flux - which controls the transition between the two growth modes - may be regulated by the initial reservoir of solids in the disc or the presence of more distant giant planets that can halt the radial flow of pebbles. | formation of planetary systems by pebble accretion and migration. how the radial pebble flux determines a terrestrial-planet or super-earth growth mode |
in the present paper we generate a set of solutions describing the interior of a compact star under f(r,t) theory of gravity which admits conformal motion. an extension of general relativity, the f(r,t) gravity is associated to ricci scalar r and the trace of the energy-momentum tensor t. to handle the einstein field equations in the form of differential equations of second order, first of all we adopt the lie algebra with conformal killing vectors (ckv) which enable one to get a solvable form of such equations and second we consider the equation of state (eos) p=ω ρ with 0<ω <1 for the fluid distribution consisting of normal matter, ω being the eos parameter. we therefore analytically explore several physical aspects of the model to represent behavior of the compact stars such as—energy conditions, tov equation, stability of the system, buchdahl condition, compactness and redshift. it is checked that the physical validity and the acceptability of the present model within the specified observational constraint in connection to a dozen of the compact star candidates are quite satisfactory. | compact stars in f(r,t) gravity |
we present light curves from a magnitude limited set of stars and other stationary luminous objects from the tess full frame images, as reduced by the mit quick look pipeline (qlp). our light curves cover the full two-year tess primary mission and include ∼14,770,000 and ∼9,600,000 individual light curve segments in the southern and northern ecliptic hemispheres, respectively. we describe the detrending techniques we used to create the light curves, and compare the noise properties with theoretical expectations. all of the qlp light curves are available at mast as a high level science product (hlsp) via doi:10.17909/t9-r086-e880 (https://archive.stsci.edu/hlsp/qlp). this is the largest collection of tess photometry available to the public to date. | photometry of 10 million stars from the first two years of tess full frame images: part ii |
eleven hours after the detection of gravitational wave source gw170817 by the laser interferometer gravitational-wave observatory and virgo interferometers, an associated optical transient, sss17a, was identified in the galaxy ngc 4993. although the gravitational wave data indicate that gw170817 is consistent with the merger of two compact objects, the electromagnetic observations provide independent constraints on the nature of that system. we synthesize the optical to near-infrared photometry and spectroscopy of sss17a collected by the one-meter two-hemisphere collaboration, finding that sss17a is unlike other known transients. the source is best described by theoretical models of a kilonova consisting of radioactive elements produced by rapid neutron capture (the r-process). we conclude that sss17a was the result of a binary neutron star merger, reinforcing the gravitational wave result. | electromagnetic evidence that sss17a is the result of a binary neutron star merger |
we present the first limits on the epoch of reionization 21 cm h i power spectra, in the redshift range z = 7.9-10.6, using the low-frequency array (lofar) high-band antenna (hba). in total, 13.0 hr of data were used from observations centered on the north celestial pole. after subtraction of the sky model and the noise bias, we detect a non-zero {{{δ }}}{{i}}2={(56+/- 13{mk})}2 (1-σ) excess variance and a best 2-σ upper limit of {{{δ }}}212< {(79.6{mk})}2 at k = 0.053 h cmpc-1 in the range z = 9.6-10.6. the excess variance decreases when optimizing the smoothness of the direction- and frequency-dependent gain calibration, and with increasing the completeness of the sky model. it is likely caused by (i) residual side-lobe noise on calibration baselines, (ii) leverage due to nonlinear effects, (iii) noise and ionosphere-induced gain errors, or a combination thereof. further analyses of the excess variance will be discussed in forthcoming publications. | upper limits on the 21 cm epoch of reionization power spectrum from one night with lofar |
we present results on the dust attenuation curve of z ∼ 2 galaxies using early observations from the mosfire deep evolution field survey. our sample consists of 224 star-forming galaxies with zspec = 1.36-2.59 and high signal-to-noise ratio measurements of hα and hβ obtained with keck/mosfire. we construct composite spectral energy distributions (seds) of galaxies in bins of balmer decrement to measure the attenuation curve. we find a curve that is similar to the smc extinction curve at λ ≳ 2500 å. at shorter wavelengths, the shape is identical to that of the calzetti et al. relation, but with a lower normalization. hence, the new attenuation curve results in star formation rates (sfrs) that are ≈ 20% lower, and stellar masses that are {δ }{log}({m}*{/m}⊙ )≃ 0.16 dex lower, than those obtained with the calzetti relation. we find that the difference in the total attenuation of the ionized gas and stellar continuum correlates strongly with sfr, such that for dust-corrected sfrs ≳ 20 m⊙ yr-1, assuming a chabrier initial mass function, the nebular emission lines suffer an increasing degree of obscuration relative to the continuum. a simple model that can account for these trends is one in which the uv through optical stellar continuum is dominated by a population of less-reddened stars, while the nebular line and bolometric luminosities become increasingly dominated by dustier stellar populations for galaxies with large sfrs, as a result of the increased dust enrichment that accompanies such galaxies. consequently, uv- and sed-based sfrs may underestimate the total sfr at even modest levels of ≈20 m⊙ yr-1. based on data obtained at the w.m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa, and was made possible by the generous financial support of the w.m. keck foundation. | the mosdef survey: measurements of balmer decrements and the dust attenuation curve at redshifts z ~ 1.4-2.6 |
long-duration γ-ray bursts (grbs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. they are characterized by an initial phase of bright and highly variable radiation in the kiloelectronvolt-to-megaelectronvolt band, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission1,2. subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands1-6. the afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock7-9. recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from grb 190114c10,11. here we report multi-frequency observations of grb 190114c, and study the evolution in time of the grb emission across 17 orders of magnitude in energy, from 5 × 10-6 to 1012 electronvolts. we find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. this component is associated with the afterglow and is satisfactorily explained by inverse compton up-scattering of synchrotron photons by high-energy electrons. we find that the conditions required to account for the observed teraelectronvolt component are typical for grbs, supporting the possibility that inverse compton emission is commonly produced in grbs. | observation of inverse compton emission from a long γ-ray burst |
ensemble studies of red-giant stars with exquisite asteroseismic (kepler), spectroscopic (apogee), and astrometric (gaia) constraints offer a novel opportunity to recast and address long-standing questions concerning the evolution of stars and of the galaxy. here, we infer masses and ages for nearly 5400 giants with available kepler light curves and apogee spectra using the code param, and discuss some of the systematics that may affect the accuracy of the inferred stellar properties. we then present patterns in mass, evolutionary state, age, chemical abundance, and orbital parameters that we deem robust against the systematic uncertainties explored. first, we look at age-chemical-abundances ([fe/h] and [α/fe]) relations. we find a dearth of young, metal-rich ([fe/h] > 0.2) stars, and the existence of a significant population of old (8-9 gyr), low-[α/fe], super-solar metallicity stars, reminiscent of the age and metallicity of the well-studied open cluster ngc 6791. the age-chemo-kinematic properties of these stars indicate that efficient radial migration happens in the thin disc. we find that ages and masses of the nearly 400 α-element-rich red-giant-branch (rgb) stars in our sample are compatible with those of an old (∼11 gyr), nearly coeval, chemical-thick disc population. using a statistical model, we show that the width of the observed age distribution is dominated by the random uncertainties on age, and that the spread of the inferred intrinsic age distribution is such that 95% of the population was born within ∼1.5 gyr. moreover, we find a difference in the vertical velocity dispersion between low- and high-[α/fe] populations. this discontinuity, together with the chemical one in the [α/fe] versus [fe/h] diagram, and with the inferred age distributions, not only confirms the different chemo-dynamical histories of the chemical-thick and thin discs, but it is also suggestive of a halt in the star formation (quenching) after the formation of the chemical-thick disc. we then exploit the almost coeval α-rich population to gain insight into processes that may have altered the mass of a star along its evolution, which are key to improving the mapping of the current, observed, stellar mass to the initial mass and thus to the age. comparing the mass distribution of stars on the lower rgb (r < 11 r⊙) with those in the red clump (rc), we find evidence for a mean integrated rgb mass loss ⟨δm⟩ = 0.10 ± 0.02 m⊙. finally, we find that the occurrence of massive (m ≳ 1.1 m⊙) α-rich stars is of the order of 5% on the rgb, and significantly higher in the rc, supporting the scenario in which most of these stars had undergone an interaction with a companion. table c.1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/645/a85 | age dissection of the milky way discs: red giants in the kepler field |
we present a new method to detect planetary transits from time-series photometry, the transit least squares (tls) algorithm. tls searches for transit-like features while taking the stellar limb darkening and planetary ingress and egress into account. we have optimized tls for both signal detection efficiency (sde) of small planets and computational speed. tls analyses the entire, unbinned phase-folded light curve. we compensated for the higher computational load by (i.) using algorithms such as "mergesort" (for the trial orbital phases) and by (ii.) restricting the trial transit durations to a smaller range that encompasses all known planets, and using stellar density priors where available. a typical k2 light curve, including 80 d of observations at a cadence of 30 min, can be searched with tls in ∼10 s real time on a standard laptop computer, as fast as the widely used box least squares (bls) algorithm. we perform a transit injection-retrieval experiment of earth-sized planets around sun-like stars using synthetic light curves with 110 ppm white noise per 30 min cadence, corresponding to a photometrically quiet kp = 12 star observed with kepler. we determine the sde thresholds for both bls and tls to reach a false positive rate of 1% to be sde = 7 in both cases. the resulting true positive (or recovery) rates are ∼93% for tls and ∼76% for bls, implying more reliable detections with tls. we also test tls with the k2 light curve of the trappist-1 system and find six of seven earth-sized planets using an iterative search for increasingly lower signal detection efficiency, the phase-folded transit of the seventh planet being affected by a stellar flare. tls is more reliable than bls in finding any kind of transiting planet but it is particularly suited for the detection of small planets in long time series from kepler, tess, and plato. we make our python implementation of tls publicly available. | optimized transit detection algorithm to search for periodic transits of small planets |
geochemical and astronomical evidence demonstrates that planet formation occurred in two spatially and temporally separated reservoirs. the origin of this dichotomy is unknown. we use numerical models to investigate how the evolution of the solar protoplanetary disk influenced the timing of protoplanet formation and their internal evolution. migration of the water snow line can generate two distinct bursts of planetesimal formation that sample different source regions. these reservoirs evolve in divergent geophysical modes and develop distinct volatile contents, consistent with constraints from accretion chronology, thermochemistry, and the mass divergence of inner and outer solar system. our simulations suggest that the compositional fractionation and isotopic dichotomy of the solar system was initiated by the interplay between disk dynamics, heterogeneous accretion, and internal evolution of forming protoplanets. | bifurcation of planetary building blocks during solar system formation |
following the discovery of the gravitational-wave source gw170817 by three laser interferometer gravitational-wave observatory (ligo)/virgo antennae (abbott et al., 2017a), the master global robotic net telescopes obtained the first image of the ngc 4993 host galaxy. an optical transient, master otj130948.10-232253.3/sss17a was later found, which appears to be a kilonova resulting from the merger of two neutron stars (nss). here we describe this independent detection and photometry of the kilonova made in white light, and in b, v, and r filters. we note that the luminosity of this kilonova in ngc 4993 is very close to those measured for other kilonovae possibly associated with gamma-ray burst (grb) 130603 and grb 080503. | master optical detection of the first ligo/virgo neutron star binary merger gw170817 |
atacama large millimeter array (alma) surveys have suggested that the dust in class ii disks may not be enough to explain the averaged solid mass in exoplanets, under the assumption that the mm disk continuum emission is optically thin. this optically thin assumption seems to be supported by recent disk substructures at high angular resolution project (dsharp) observations where the measured optical depths are mostly less than one. however, we point out that dust scattering can considerably reduce the emission from an optically thick region. if that scattering is ignored, an optically thick disk with scattering can be misidentified as an optically thin disk. dust scattering in more inclined disks can reduce the intensity even further, making the disk look even fainter. the measured optical depth of ∼0.6 in several dsharp disks can be naturally explained by optically thick dust with an albedo of ∼0.9 at 1.25 mm. using the dsharp opacity, this albedo corresponds to a dust population with the maximum grain size (s max) of 0.1-1 mm. for optically thick scattering disks, the measured spectral index α can be either larger or smaller than 2 depending on whether the dust albedo increases or decreases with wavelength. we describe how this optically thick scattering scenario could explain the observed scaling between submm continuum sizes and luminosities, and might help ease the tension between the dust size constraints from polarization and dust continuum measurements. we suggest that a significant amount of disk mass can be hidden from alma observations and longer wavelength observations (e.g., very large array or square kilometre array) are desired to probe the dust mass in disks. | one solution to the mass budget problem for planet formation: optically thick disks with dust scattering |
in optics, the ability to measure individual quanta of light (photons) enables a great many applications, ranging from dynamic imaging within living organisms to secure quantum communication. pioneering photon counting experiments, such as the intensity interferometry performed by hanbury brown and twiss to measure the angular width of visible stars, have played a critical role in our understanding of the full quantum nature of light. as with matter at the atomic scale, the laws of quantum mechanics also govern the properties of macroscopic mechanical objects, providing fundamental quantum limits to the sensitivity of mechanical sensors and transducers. current research in cavity optomechanics seeks to use light to explore the quantum properties of mechanical systems ranging in size from kilogram-mass mirrors to nanoscale membranes, as well as to develop technologies for precision sensing and quantum information processing. here we use an optical probe and single-photon detection to study the acoustic emission and absorption processes in a silicon nanomechanical resonator, and perform a measurement similar to that used by hanbury brown and twiss to measure correlations in the emitted phonons as the resonator undergoes a parametric instability formally equivalent to that of a laser. owing to the cavity-enhanced coupling of light with mechanical motion, this effective phonon counting technique has a noise equivalent phonon sensitivity of 0.89 +/- 0.05. with straightforward improvements to this method, a variety of quantum state engineering tasks using mesoscopic mechanical resonators would be enabled, including the generation and heralding of single-phonon fock states and the quantum entanglement of remote mechanical elements. | phonon counting and intensity interferometry of a nanomechanical resonator |
we present a comprehensive study of the abundance evolution of the elements from h to u in the milky way halo and local disc. we use a consistent chemical evolution model, metallicity-dependent isotopic yields from low and intermediate mass stars and yields from massive stars which include, for the first time, the combined effect of metallicity, mass loss, and rotation for a large grid of stellar masses and for all stages of stellar evolution. the yields of massive stars are weighted by a metallicity-dependent function of the rotational velocities, constrained by observations as to obtain a primary-like 14n behaviour at low metallicity and to avoid overproduction of s-elements at intermediate metallicities. we show that the solar system isotopic composition can be reproduced to better than a factor of 2 for isotopes up to the fe-peak, and at the 10 per cent level for most pure s-isotopes, both light ones (resulting from the weak s-process in rotating massive stars) and the heavy ones (resulting from the main s-process in low and intermediate mass stars). we conclude that the light element primary process (lepp), invoked to explain the apparent abundance deficiency of the s-elements with a < 100, is not necessary. we also reproduce the evolution of the heavy to light s-elements abundance ratio ([hs/ls]) - recently observed in unevolved thin disc stars - as a result of the contribution of rotating massive stars at sub-solar metallicities. we find that those stars produce primary f and dominate its solar abundance and we confirm their role in the observed primary behaviour of n. in contrast, we show that their action is insufficient to explain the small observed values of ^{12}c/^{13}c in halo red giants, which is rather due to internal processes in those stars. | chemical evolution with rotating massive star yields - i. the solar neighbourhood and the s-process elements |
we report two secure ( $z=3.775,4.012$ ) and one tentative (z ≈ 3.767) spectroscopic confirmations of massive and quiescent galaxies through k-band observations with keck/mosfire and very large telescope/x-shooter. the stellar continuum emission, absence of strong nebular emission lines, and lack of significant far-infrared detections confirm the passive nature of these objects, disfavoring the alternative solution of low-redshift dusty star-forming interlopers. we derive stellar masses of log(m⋆/m⊙) ∼ 11 and ongoing star formation rates placing these galaxies ≳1-2 dex below the main sequence at their redshifts. the adopted parameterization of the star formation history suggests that these sources experienced a strong ( $\langle \mathrm{sfr}\rangle \sim 1200\mbox{--}3500$ m⊙ yr-1) and short (∼50 myr) burst of star formation, peaking ∼150-500 myr before the time of observation, all properties reminiscent of the characteristics of submillimeter galaxies (smgs) at z > 4. we investigate this connection by comparing the comoving number densities and the properties of these two populations. we find a fair agreement only with the deepest submillimeter surveys detecting not only the most extreme starbursts but also more normal galaxies. we support these findings by further exploring the illustris tng cosmological simulation, retrieving populations of both fully quenched massive galaxies at z ∼ 3-4 and smgs at z ∼ 4-5, with number densities and properties in agreement with the observations at z ∼ 3 but in increasing tension at higher redshift. nevertheless, as suggested by the observations, not all of the progenitors of quiescent galaxies at these redshifts shine as bright smgs in their past, and, similarly, not all bright smgs quench by z ∼ 3, both fractions depending on the threshold assumed to define the smgs themselves. | quiescent galaxies 1.5 billion years after the big bang and their progenitors |
we review the progress in modeling the galaxy population in hydrodynamical simulations of the λcdm cosmogony. state-of-the-art simulations now broadly reproduce the observed spatial clustering of galaxies; the distributions of key characteristics, such as mass, size, and sfr; and scaling relations connecting diverse properties to mass. such improvements engender confidence in the insight drawn from simulations. many important outcomes, however, particularly the properties of circumgalactic gas, are sensitive to the details of the subgrid models used to approximate the macroscopic effects of unresolved physics, such as feedback processes. we compare the outcomes of leading simulation suites with observations, and with each other, to identify the enduring successes they have cultivated and the outstanding challenges to be tackled with the next generation of models. our key conclusions include the following:<label>■</label>realistic galaxies can be reproduced by calibrating the ill-constrained parameters of subgrid feedback models. feedback is dominated by stars and black holes in low-mass and high-mass galaxies, respectively.<label>■</label>adjusting or disabling the processes implemented in simulations can elucidate their impact on observables, but outcomes can be degenerate.<label>■</label>similar galaxy populations can emerge in simulations with dissimilar feedback implementations. however, these models generally predict markedly different gas flow rates into, and out of, galaxies and their halos. cgm observations are thus a promising means of breaking this degeneracy and guiding the development of new feedback models. | hydrodynamical simulations of the galaxy population: enduring successes and outstanding challenges |
astronomers have discovered thousands of planets outside the solar system1, most of which orbit stars that will eventually evolve into red giants and then into white dwarfs. during the red giant phase, any close-orbiting planets will be engulfed by the star2, but more distant planets can survive this phase and remain in orbit around the white dwarf3,4. some white dwarfs show evidence for rocky material floating in their atmospheres5, in warm debris disks6-9 or orbiting very closely10-12, which has been interpreted as the debris of rocky planets that were scattered inwards and tidally disrupted13. recently, the discovery of a gaseous debris disk with a composition similar to that of ice giant planets14 demonstrated that massive planets might also find their way into tight orbits around white dwarfs, but it is unclear whether these planets can survive the journey. so far, no intact planets have been detected in close orbits around white dwarfs. here we report the observation of a giant planet candidate transiting the white dwarf wd 1856+534 (tic 267574918) every 1.4 days. we observed and modelled the periodic dimming of the white dwarf caused by the planet candidate passing in front of the star in its orbit. the planet candidate is roughly the same size as jupiter and is no more than 14 times as massive (with 95 per cent confidence). other cases of white dwarfs with close brown dwarf or stellar companions are explained as the consequence of common-envelope evolution, wherein the original orbit is enveloped during the red giant phase and shrinks owing to friction. in this case, however, the long orbital period (compared with other white dwarfs with close brown dwarf or stellar companions) and low mass of the planet candidate make common-envelope evolution less likely. instead, our findings for the wd 1856+534 system indicate that giant planets can be scattered into tight orbits without being tidally disrupted, motivating the search for smaller transiting planets around white dwarfs. | a giant planet candidate transiting a white dwarf |
launched on 12 aug. 2018, nasa's parker solar probe had completed 13 of its scheduled 24 orbits around the sun by nov. 2022. the mission's primary science goal is to determine the structure and dynamics of the sun's coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. parker solar probe returned a treasure trove of science data that far exceeded quality, significance, and quantity expectations, leading to a significant number of discoveries reported in nearly 700 peer-reviewed publications. the first four years of the 7-year primary mission duration have been mostly during solar minimum conditions with few major solar events. starting with orbit 8 (i.e., 28 apr. 2021), parker flew through the magnetically dominated corona, i.e., sub-alfvénic solar wind, which is one of the mission's primary objectives. in this paper, we present an overview of the scientific advances made mainly during the first four years of the parker solar probe mission, which go well beyond the three science objectives that are: (1) trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) explore mechanisms that accelerate and transport energetic particles. | parker solar probe: four years of discoveries at solar cycle minimum |
galaxies fall into two clearly distinct types: `blue-sequence' galaxies which are rapidly forming young stars, and `red-sequence' galaxies in which star formation has almost completely ceased. most galaxies more massive than 3 × 1010 m⊙ follow the red sequence, while less massive central galaxies lie on the blue sequence. we show that these sequences are created by a competition between star formation-driven outflows and gas accretion on to the supermassive black hole at the galaxy's centre. we develop a simple analytic model for this interaction. in galaxies less massive than 3 × 1010 m⊙, young stars and supernovae drive a high-entropy outflow which is more buoyant than any tenuous corona. the outflow balances the rate of gas inflow, preventing high gas densities building up in the central regions. more massive galaxies, however, are surrounded by an increasingly hot corona. above a halo mass of ∼1012 m⊙, the outflow ceases to be buoyant and star formation is unable to prevent the build-up of gas in the central regions. this triggers a strongly non-linear response from the black hole. its accretion rate rises rapidly, heating the galaxy's corona, disrupting the incoming supply of cool gas and starving the galaxy of the fuel for star formation. the host galaxy makes a transition to the red sequence, and further growth predominantly occurs through galaxy mergers. we show that the analytic model provides a good description of galaxy evolution in the eagle hydrodynamic simulations. so long as star formation-driven outflows are present, the transition mass scale is almost independent of subgrid parameter choice. | the dark nemesis of galaxy formation: why hot haloes trigger black hole growth and bring star formation to an end |
we present the first extensive radio to γ-ray observations of a fast-rising blue optical transient, at 2018cow, over its first ∼100 days. at 2018cow rose over a few days to a peak luminosity l pk ∼ 4 × 1044 erg s-1, exceeding that of superluminous supernovae (sne), before declining as l ∝ t -2. initial spectra at δt ≲ 15 days were mostly featureless and indicated large expansion velocities v ∼ 0.1c and temperatures reaching t ∼ 3 × 104 k. later spectra revealed a persistent optically thick photosphere and the emergence of h and he emission features with v ∼ 4000 km s-1 with no evidence for ejecta cooling. our broadband monitoring revealed a hard x-ray spectral component at e ≥ 10 kev, in addition to luminous and highly variable soft x-rays, with properties unprecedented among astronomical transients. an abrupt change in the x-ray decay rate and variability appears to accompany the change in optical spectral properties. at 2018cow showed bright radio emission consistent with the interaction of a blast wave with v sh ∼ 0.1c with a dense environment (\dot{m}∼ {10}-3-{10}-4 {m}⊙ {yr}}-1 for vw= 1000 km s-1). while these properties exclude 56ni-powered transients, our multiwavelength analysis instead indicates that at 2018cow harbored a “central engine,” either a compact object (magnetar or black hole) or an embedded internal shock produced by interaction with a compact, dense circumstellar medium. the engine released ∼1050-1051.5 erg over ∼103-105 s and resides within low-mass fast-moving material with equatorial-polar density asymmetry (m ej,fast ≲ 0.3 m ⊙). successful sne from low-mass h-rich stars (like electron-capture sne) or failed explosions from blue supergiants satisfy these constraints. intermediate-mass black holes are disfavored by the large environmental density probed by the radio observations. | an embedded x-ray source shines through the aspherical at 2018cow: revealing the inner workings of the most luminous fast-evolving optical transients |
the discovery of gw170817 with gravitational waves (gws) and electromagnetic (em) radiation is prompting new questions in strong-gravity astrophysics. importantly, it remains unknown whether the progenitor of the merger comprised two neutron stars (nss) or a ns and a black hole (bh). using new numerical-relativity simulations and incorporating modeling uncertainties, we produce novel gw and em observables for ns-bh mergers with similar masses. a joint analysis of gw and em measurements reveals that if gw170817 is a ns-bh merger, ≲40 % of the binary parameters consistent with the gw data are compatible with em observations. | distinguishing the nature of comparable-mass neutron star binary systems with multimessenger observations: gw170817 case study |
recent observations of gn-z11 with jwst/nirspec revealed numerous oxygen, carbon, nitrogen, and helium emission lines at z = 10.6. using the measured line fluxes, we derive abundance ratios of individual elements within the interstellar medium (ism) of this superluminous galaxy. driven by the unusually-bright n iii] λ1750 and n iv] λ1486 emission lines (and by comparison, faint o iii] λλ1660, 1666 lines), our fiducial model prefers log (n/o) > -0.25, greater than four times solar and in stark contrast to lower-redshift star-forming galaxies. the derived log (c/o) > -0.78, (≈30 per cent solar) is also elevated with respect to galaxies of similar metallicity (12 + log (o/h) ≈ 7.82), although less at odds with lower-redshift measurements. we explore the feasibility of achieving these abundance ratios via several enrichment mechanisms using metal yields available in the literature. given the long time-scale typically expected to enrich nitrogen with stellar winds, traditional scenarios require a very fine-tuned formation history to reproduce such an elevated n/o. we find no compelling evidence that nitrogen enhancement in gn-z11 can be explained by enrichment from metal-free population iii stars. interestingly, yields from runaway stellar collisions in a dense stellar cluster or a tidal disruption event provide promising solutions to give rise to these unusual emission lines at z = 10.6, and explain the resemblance between gn-z11 and a nitrogen-loud quasar. these recent observations showcase the new frontier opened by jwst to constrain galactic enrichment and stellar evolution within 440 myr of the big bang. | nitrogen enhancements 440 myr after the big bang: supersolar n/o, a tidal disruption event, or a dense stellar cluster in gn-z11? |
the brightness of the tip of the red-giant branch (trgb) allows one to constrain novel energy losses that would lead to a larger core mass at helium ignition and, thus, to a brighter trgb than expected by standard stellar models. the required absolute trgb calibrations strongly improve with reliable geometric distances that have become available for the galaxy ngc 4258 that hosts a water megamaser and to the large magellanic cloud based on 20 detached eclipsing binaries. moreover, we revise a previous trgb calibration in the globular cluster ω centauri with a recent kinematical distance determination based on gaia data release 2. all of these calibrations have similar uncertainties, and they agree with each other and with recent dedicated stellar models. using ngc 4258 as the cleanest extragalactic case, we thus find an updated constraint on the axion-electron coupling of ga e<1.6 ×10-13 and μν<1.5 ×10-12μb (95% c.l.) on a possible neutrino dipole moment, whereas ω centauri as the best galactic target provides instead ga e<1.3 ×10-13 and μν<1.2 ×10-12μb. the reduced observational errors imply that stellar evolution theory and bolometric corrections begin to dominate the overall uncertainties. | axion and neutrino bounds improved with new calibrations of the tip of the red-giant branch using geometric distance determinations |
the primary method for inferring the stellar mass (m*) of a galaxy is through spectral energy distribution (sed) modeling. however, the technique rests on assumptions such as the galaxy star formation history (sfh) and dust attenuation law that can severely impact the accuracy of derived physical properties from sed modeling. here we examine the effect that the assumed sfh has on the stellar properties inferred from sed fitting by ground-truthing them against mock observations of high-resolution cosmological hydrodynamic galaxy formation simulations. classically, sfhs are modeled with simplified parameterized functional forms, but these forms are unlikely to capture the true diversity of galaxy sfhs and may impose systematic biases with underreported uncertainties on results. we demonstrate that flexible nonparametric sfhs outperform traditional parametric forms in capturing variations in galaxy sfhs and, as a result, lead to significantly improved stellar masses in sed fitting. we find a decrease in the average bias of 0.4 dex with a delayed-τ model to a bias under 0.1 dex for the nonparametric model, though this is heavily dependent on the choice of prior for the nonparametric model. similarly, using nonparametric sfhs in sed fitting results in increased accuracy in recovered galaxy star formation rates and stellar ages. | how well can we measure the stellar mass of a galaxy: the impact of the assumed star formation history model in sed fitting |
observations have found black holes spanning 10 orders of magnitude in mass across most of cosmic history. the kerr black hole solution is, however, provisional as its behavior at infinity is incompatible with an expanding universe. black hole models with realistic behavior at infinity predict that the gravitating mass of a black hole can increase with the expansion of the universe independently of accretion or mergers, in a manner that depends on the black hole's interior solution. we test this prediction by considering the growth of supermassive black holes in elliptical galaxies over 0 < z ≲ 2.5. we find evidence for cosmologically coupled mass growth among these black holes, with zero cosmological coupling excluded at 99.98% confidence. the redshift dependence of the mass growth implies that, at z ≲ 7, black holes contribute an effectively constant cosmological energy density to friedmann's equations. the continuity equation then requires that black holes contribute cosmologically as vacuum energy. we further show that black hole production from the cosmic star formation history gives the value of ωλ measured by planck while being consistent with constraints from massive compact halo objects. we thus propose that stellar remnant black holes are the astrophysical origin of dark energy, explaining the onset of accelerating expansion at z ~ 0.7. | observational evidence for cosmological coupling of black holes and its implications for an astrophysical source of dark energy |
we analyse scaling relations and evolution histories of galaxy sizes in tng100, part of the illustristng simulation suite. observational qualitative trends of size with stellar mass, star formation rate and redshift are reproduced, and a quantitative comparison of projected r band sizes at 0 ≲ z ≲ 2 shows agreement to much better than 0.25 dex. we follow populations of z = 0 galaxies with a range of masses backwards in time along their main progenitor branches, distinguishing between main-sequence and quenched galaxies. our main findings are as follows. (i) at m*, z = 0 ≳ 109.5 m⊙, the evolution of the median main progenitor differs, with quenched galaxies hardly growing in median size before quenching, whereas main-sequence galaxies grow their median size continuously, thus opening a gap from the progenitors of quenched galaxies. this is partly because the main-sequence high-redshift progenitors of quenched z = 0 galaxies are drawn from the lower end of the size distribution of the overall population of main-sequence high-redshift galaxies. (ii) quenched galaxies with m*, z = 0 ≳ 109.5 m⊙ experience a steep size growth on the size-mass plane after their quenching time, but with the exception of galaxies with m*, z = 0 ≳ 1011 m⊙, the size growth after quenching is small in absolute terms, such that most of the size (and mass) growth of quenched galaxies (and its variation among them) occurs while they are still on the main sequence. after they become quenched, the size growth rate of quenched galaxies as a function of time, as opposed to versus mass, is similar to that of main-sequence galaxies. hence, the size gap is retained down to z = 0. | the size evolution of star-forming and quenched galaxies in the illustristng simulation |
in addition to long-lived radioactive nuclei like u and th isotopes, which have been used to measure the age of thegalaxy, also radioactive nuclei with half-lives between 0.1 and 100 million years (short-lived radionuclides, slrs) were present in the early solar system (ess), as indicated by high-precision meteoritic analysis. we review the most recent meteoritic data and describe the nuclear interaction processes responsible for the creation of slrs in different types of stars and supernovae. we show how the evolution of radionuclide abundances in the milky way galaxy can be calculated based on their stellar production. by comparing predictions for the evolution of galactic abundances to the meteoritic data we can build up a time line for the nucleosynthetic events that predated the birth of the sun, and investigate the lifetime of the stellar nursery where the sun was born. we then review the scenarios for the circumstances and the environment of the birth of the sun, within such a stellar nursery, that have been invoked to explain the abundances in the ess of the slrs with the shortest lives - of the order of million years or less. finally, we describe how the heat generated by radioactive decay and in particular by the abundant 26al in the ess had important consequences for the thermo-mechanical and chemical evolution of planetesimals, and discuss possible implications on the habitability of terrestrial-like planets. we conclude with a set of open questions and future directions related to our understanding of the nucleosynthetic processes responsible for the production of slrs in stars, their evolution in the galaxy, the birth of the sun, and the connection with the habitability of extra-solar planets. | radioactive nuclei from cosmochronology to habitability |
coronal jets represent important manifestations of ubiquitous solar transients, which may be the source of significant mass and energy input to the upper solar atmosphere and the solar wind. while the energy involved in a jet-like event is smaller than that of "nominal" solar flares and coronal mass ejections (cmes), jets share many common properties with these phenomena, in particular, the explosive magnetically driven dynamics. studies of jets could, therefore, provide critical insight for understanding the larger, more complex drivers of the solar activity. on the other side of the size-spectrum, the study of jets could also supply important clues on the physics of transients close or at the limit of the current spatial resolution such as spicules. furthermore, jet phenomena may hint to basic process for heating the corona and accelerating the solar wind; consequently their study gives us the opportunity to attack a broad range of solar-heliospheric problems. | solar coronal jets: observations, theory, and modeling |
the carmenes radial velocity (rv) survey is observing 324 m dwarfs to search for any orbiting planets. in this paper, we present the survey sample by publishing one carmenes spectrum for each m dwarf. these spectra cover the wavelength range 520-1710 nm at a resolution of at least r >80 000, and we measure its rv, hα emission, and projected rotation velocity. we present an atlas of high-resolution m-dwarf spectra and compare the spectra to atmospheric models. to quantify the rv precision that can be achieved in low-mass stars over the carmenes wavelength range, we analyze our empirical information on the rv precision from more than 6500 observations. we compare our high-resolution m-dwarf spectra to atmospheric models where we determine the spectroscopic rv information content, q, and signal-to-noise ratio. we find that for all m-type dwarfs, the highest rv precision can be reached in the wavelength range 700-900 nm. observations at longer wavelengths are equally precise only at the very latest spectral types (m8 and m9). we demonstrate that in this spectroscopic range, the large amount of absorption features compensates for the intrinsic faintness of an m7 star. to reach an rv precision of 1 m s-1 in very low mass m dwarfs at longer wavelengths likely requires the use of a 10 m class telescope. for spectral types m6 and earlier, the combination of a red visual and a near-infrared spectrograph is ideal to search for low-mass planets and to distinguish between planets and stellar variability. at a 4 m class telescope, an instrument like carmenes has the potential to push the rv precision well below the typical jitter level of 3-4 m s-1. | the carmenes search for exoplanets around m dwarfs. high-resolution optical and near-infrared spectroscopy of 324 survey stars |
we present a study of 33 kepler planet-candidate host stars for which asteroseismic observations have sufficiently high signal-to-noise ratio to allow extraction of individual pulsation frequencies. we implement a new bayesian scheme that is flexible in its input to process individual oscillation frequencies, combinations of them, and average asteroseismic parameters, and derive robust fundamental properties for these targets. applying this scheme to grids of evolutionary models yields stellar properties with median statistical uncertainties of 1.2 per cent (radius), 1.7 per cent (density), 3.3 per cent (mass), 4.4 per cent (distance), and 14 per cent (age), making this the exoplanet host-star sample with the most precise and uniformly determined fundamental parameters to date. we assess the systematics from changes in the solar abundances and mixing-length parameter, showing that they are smaller than the statistical errors. we also determine the stellar properties with three other fitting algorithms and explore the systematics arising from using different evolution and pulsation codes, resulting in 1 per cent in density and radius, and 2 per cent and 7 per cent in mass and age, respectively. we confirm previous findings of the initial helium abundance being a source of systematics comparable to our statistical uncertainties, and discuss future prospects for constraining this parameter by combining asteroseismology and data from space missions. finally, we compare our derived properties with those obtained using the global average asteroseismic observables along with effective temperature and metallicity, finding excellent level of agreement. owing to selection effects, our results show that the majority of the high signal-to-noise ratio asteroseismic kepler host stars are older than the sun. | ages and fundamental properties of kepler exoplanet host stars from asteroseismology |
information on the phase structure of strongly interacting matter at high baryon densities can be gained from observations of neutron stars and their detailed analysis. in the present work bayesian inference methods are used to set constraints on the speed of sound in the interior of neutron stars, based on recent multimessenger data in combination with limiting conditions from nuclear physics at low densities. two general parametric representations are introduced for the sound speed cs in order to examine the independence with respect to choices for the parametrization of priors. credible regions for neutron star properties are analyzed, in particular with reference to the quest for possible phase transitions in cold dense matter. the evaluation of bayes factors implies extreme evidence for a violation of the conformal bound, cs2≤1 /3 , inside neutron stars. given the presently existing data base, it can be concluded that the occurrence of a first-order phase transition in the core of even a two-solar-mass neutron star is unlikely, while a continuous crossover cannot be ruled out. at the same time it is pointed out that the discovery of a superheavy neutron star with a mass m ∼2.3 - 2.4 m⊙ would strengthen evidence for a phase change in the deep interior of the star. | inference of the sound speed and related properties of neutron stars |
probing the origin of r-process elements in the universe represents a multidisciplinary challenge. we review the observational evidence that probes the properties of r-process sites, and address them using galactic chemical evolution simulations, binary population synthesis models, and nucleosynthesis calculations. our motivation is to define which astrophysical sites have significantly contributed to the total mass of r-process elements present in our galaxy. we found discrepancies with the neutron star (ns-ns) merger scenario. when we assume that they are the only site, the decreasing trend of [eu/fe] at [fe/h] > -1 in the disk of the milky way cannot be reproduced while accounting for the delay-time distribution (dtd) of coalescence times (∝t -1) derived from short gamma-ray bursts (grbs) and population synthesis models. steeper dtd functions (∝t -1.5) or power laws combined with a strong burst of mergers before the onset of supernovae (sne) ia can reproduce the [eu/fe] trend, but this scenario is inconsistent with the similar fraction of short grbs and sne ia occurring in early-type galaxies, and it reduces the probability of detecting gw170817 in an early-type galaxy. one solution is to assume an additional production site of eu that would be active in the early universe, but would fade away with increasing metallicity. if this is correct, this additional site could be responsible for roughly 50% of the eu production in the early universe before the onset of sne ia. rare classes of supernovae could be this additional r-process source, but hydrodynamic simulations still need to ensure the conditions for a robust r-process pattern. | neutron star mergers might not be the only source of r-process elements in the milky way |
we present starforge (star formation in gaseous environments): a new numerical framework for 3d radiation magnetohydrodynamic (mhd) simulations of star formation that simultaneously follow the formation, accretion, evolution, and dynamics of individual stars in massive giant molecular clouds (gmcs), while accounting for stellar feedback, including jets, radiative heating and momentum, stellar winds, and supernovae. we use the gizmo code with the mfm mesh-free lagrangian mhd method, augmented with new algorithms for gravity, time-stepping, sink particle formation and accretion, stellar dynamics, and feedback coupling. we survey a wide range of numerical parameters/prescriptions for sink formation and accretion and find very small variations in star formation history and the imf (except for intentionally unphysical variations). modules for mass-injecting feedback (winds, sne, and jets) inject new gas elements on the fly, eliminating the lack of resolution in diffuse feedback cavities otherwise inherent in lagrangian methods. the treatment of radiation uses gizmo's radiative transfer solver to track five frequency bands (ir, optical, nuv, fuv, ionizing), coupling direct stellar emission and dust emission with gas heating and radiation pressure terms. we demonstrate accurate solutions for sne, winds, and radiation in problems with known similarity solutions, and show that our jet module is robust to resolution and numerical details, and agrees well with previous amr simulations. starforge can scale up to massive (>105 m⊙) gmcs on current supercomputers while predicting the stellar (≳0.1 m⊙) range of the imf, permitting simulations of both high- and low-mass cluster formation in a wide range of conditions. | starforge: towards a comprehensive numerical model of star cluster formation and feedback |
extremely irradiated hot jupiters, exoplanets reaching dayside temperatures >2000 k, stretch our understanding of planetary atmospheres and the models we use to interpret observations. while these objects are planets in every other sense, their atmospheres reach temperatures at low pressures comparable only to stellar atmospheres. in order to understand our a priori theoretical expectations for the nature of these objects, we self-consistently model a number of extreme hot jupiter scenarios with the phoenix model atmosphere code. phoenix is well-tested on objects from cool brown dwarfs to expanding supernovae shells, and its expansive opacity database from the uv to far-ir make phoenix well-suited to understanding extremely irradiated hot jupiters. we find several fundamental differences between hot jupiters at temperatures >2500 k and their cooler counterparts. first, absorption by atomic metals like fe and mg, molecules including sio and metal hydrides, and continuous opacity sources like h-, all combined with the short-wavelength output of early-type host stars, result in strong thermal inversions, without the need for tio or vo. second, many molecular species, including h2o, tio, and vo are thermally dissociated at pressures probed by transit and eclipse observations, potentially biasing retrieval algorithms that assume uniform vertical abundances. we discuss other interesting properties of these objects, as well as future prospects and predictions for observing and characterizing this unique class of astrophysical object, including the first self-consistent model of the hottest known jovian planet, kelt-9b. | extremely irradiated hot jupiters: non-oxide inversions, h- opacity, and thermal dissociation of molecules |
fast radio bursts (frbs) are millisecond-duration radio transients1,2 of unknown origin. two possible mechanisms that could generate extremely coherent emission from frbs invoke neutron star magnetospheres3-5 or relativistic shocks far from the central energy source6-8. detailed polarization observations may help us to understand the emission mechanism. however, the available frb polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters9,10 or variable polarization angles in some other apparently one-off events11,12. here we report observations of 15 bursts from frb 180301 and find various polarization angle swings in seven of them. the diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks. | diverse polarization angle swings from a repeating fast radio burst source |
light curves, explosion energies, and remnant masses are calculated for a grid of supernovae resulting from massive helium stars that have been evolved including mass loss. these presupernova stars should approximate the results of binary evolution for stars in interacting systems that lose their envelopes close to the time of helium core ignition. initial helium star masses are in the range 2.5-40 m⊙, which corresponds to main-sequence masses of about 13-90 m⊙. common sne ib and ic result from stars whose final masses are approximately 2.5-5.6 m⊙. for heavier stars, a large fraction of collapses lead to black holes, though there is an island of explodability for presupernova masses near 10 m⊙. the median neutron star mass in binaries is 1.35-1.38 m⊙, and the median black hole mass is between 9 and 11 m⊙. even though black holes less massive than 5 m⊙ are rare, they are predicted down to the maximum neutron star mass. there is no empty "gap," only a less populated mass range. for standard assumptions regarding the explosions and nucleosynthesis, the models predict light curves that are fainter than the brighter common sne ib and ic. even with a very liberal but physically plausible increase in 56ni production, the highest-energy models are fainter than 1042.6 erg s-1 at peak, and very few approach that limit. the median peak luminosity ranges from 1042.0 to 1042.3 erg s-1. possible alternatives to the standard neutrino-powered and radioactive-illuminated models are explored. magnetars are a promising alternative. several other unusual varieties of sne i at both high and low mass are explored. | the explosion of helium stars evolved with mass loss |
galaxy clusters magnify background objects through strong gravitational lensing. typical magnifications for lensed galaxies are factors of a few but can also be as high as tens or hundreds, stretching galaxies into giant arcs1,2. individual stars can attain even higher magnifications given fortuitous alignment with the lensing cluster. recently, several individual stars at redshifts between approximately 1 and 1.5 have been discovered, magnified by factors of thousands, temporarily boosted by microlensing3-6. here we report observations of a more distant and persistent magnified star at a redshift of 6.2 ± 0.1, 900 million years after the big bang. this star is magnified by a factor of thousands by the foreground galaxy cluster lens whl0137-08 (redshift 0.566), as estimated by four independent lens models. unlike previous lensed stars, the magnification and observed brightness (ab magnitude, 27.2) have remained roughly constant over 3.5 years of imaging and follow-up. the delensed absolute uv magnitude, −10 ± 2, is consistent with a star of mass greater than 50 times the mass of the sun. confirmation and spectral classification are forthcoming from approved observations with the james webb space telescope. | a highly magnified star at redshift 6.2 |
powerful winds driven by active galactic nuclei are often thought to affect the evolution of both supermassive black holes and their host galaxies, quenching star formation and explaining the close relationship between black holes and galaxies. recent observations of large-scale molecular outflows in ultraluminous infrared galaxies support this quasar-feedback idea, because they directly trace the gas from which stars form. theoretical models suggest that these outflows originate as energy-conserving flows driven by fast accretion-disk winds. proposed connections between large-scale molecular outflows and accretion-disk activity in ultraluminous galaxies were incomplete because no accretion-disk wind had been detected. conversely, studies of powerful accretion-disk winds have until now focused only on x-ray observations of local seyfert galaxies and a few higher-redshift quasars. here we report observations of a powerful accretion-disk wind with a mildly relativistic velocity (a quarter that of light) in the x-ray spectrum of iras f11119+3257, a nearby (redshift 0.189) optically classified type 1 ultraluminous infrared galaxy hosting a powerful molecular outflow. the active galactic nucleus is responsible for about 80 per cent of the emission, with a quasar-like luminosity of 1.5 × 1046 ergs per second. the energetics of these two types of wide-angle outflows is consistent with the energy-conserving mechanism that is the basis of the quasar feedback in active galactic nuclei that lack powerful radio jets (such jets are an alternative way to drive molecular outflows). | wind from the black-hole accretion disk driving a molecular outflow in an active galaxy |
we construct a large set of dynamical models of the galactic bulge, bar and inner disc using the made-to-measure method. our models are constrained to match the red clump giant density from a combination of the vvv, ukidss and 2mass infrared surveys together with stellar kinematics in the bulge from the brava and ogle surveys, and in the entire bar region from the argos survey. we are able to recover the bar pattern speed and the stellar and dark matter mass distributions in the bar region, thus recovering the entire galactic effective potential. we find a bar pattern speed of 39.0 ± 3.5 km s- 1 kpc- 1, placing the bar corotation radius at 6.1 ± 0.5 kpc and making the milky way bar a typical fast rotator. we evaluate the stellar mass of the long bar and bulge structure to be mbar/bulge = 1.88 ± 0.12 × 1010 m⊙, larger than the mass of disc in the bar region, minner disc = 1.29 ± 0.12 × 1010 m⊙. the total dynamical mass in the bulge volume is 1.85 ± 0.05 × 1010 m⊙. thanks to more extended kinematic data sets and recent measurement of the bulge initial mass function, our models have a low dark matter fraction in the bulge of 17 ± 2 per cent. we find a dark matter density profile which flattens to a shallow cusp or core in the bulge region. finally, we find dynamical evidence for an extra central mass of ∼ 0.2 × 1010 m⊙, probably in a nuclear disc or discy pseudo-bulge. | dynamical modelling of the galactic bulge and bar: the milky way's pattern speed, stellar and dark matter mass distribution |
the orbital distribution of giant planets is crucial for understanding how terrestrial planets form and predicting yields of exoplanet surveys. here, we derive giant planets occurrence rates as a function of orbital period by taking into account the detection efficiency of the kepler and radial velocity (rv) surveys. the giant planet occurrence rates for kepler and rv show the same rising trend with increasing distance from the star. we identify a break in the rv giant planet distribution between ∼2 and 3 au—close to the location of the snow line in the solar system—after which the occurrence rate decreases with distance from the star. extrapolating a broken power-law distribution to larger semimajor axes, we find good agreement with the ∼1% planet occurrence rates from direct imaging surveys. assuming a symmetric power law, we also estimate that the occurrence of giant planets between 0.1 and 100 au is {26.6}-5.4+7.5 % for planets with masses 0.1-20 m j and decreases to {6.2}-1.2+1.5 % for planets more massive than jupiter. this implies that only a fraction of the structures detected in disks around young stars can be attributed to giant planets. various planet population synthesis models show good agreement with the observed distribution, and we show how a quantitative comparison between model and data can be used to constrain planet formation and migration mechanisms. | hints for a turnover at the snow line in the giant planet occurrence rate |
the idea of stable, localized bundles of energy has strong appeal as a model for particles. in the 1950s, john wheeler envisioned such bundles as smooth configurations of electromagnetic energy that he called geons, but none were found. instead, particle-like solutions were found in the late 1960s with the addition of a scalar field, and these were given the name boson stars. since then, boson stars find use in a wide variety of models as sources of dark matter, as black hole mimickers, in simple models of binary systems, and as a tool in finding black holes in higher dimensions with only a single killing vector. we discuss important varieties of boson stars, their dynamic properties, and some of their uses, concentrating on recent efforts. | dynamical boson stars |
we discovered 2.8 s pulsations in the x-ray emission of the ultraluminous x-ray source (ulx) m51 ulx-7 within the unseen project, which was designed to hunt for new pulsating ulxs (pulxs) with xmm-newton. the pulse shape is sinusoidal, and large variations of its amplitude were observed even within single exposures (pulsed fraction from less than 5% to 20%). source m51 ulx-7 is variable, generally observed at an x-ray luminosity between 1039 and 1040 erg s-1, located in the outskirts of the spiral galaxy m51a at a distance of 8.6 mpc. according to our analysis, the x-ray pulsar orbits in a 2 day binary with a projected semimajor axis ${a}_{{\rm{x}}}\sin i\,\simeq $ 28 lt-s. for a neutron star (ns) of 1.4 m⊙, this implies a lower limit on the companion mass of 8 m⊙, placing the system hosting m51 ulx-7 in the high-mass x-ray binary class. the barycentric pulse period decreased by ≃0.4 ms in the 31 days spanned by our 2018 may-june observations, corresponding to a spin-up rate $\dot{p}\simeq -1.5\times {10}^{-10}\,{\rm{s}}\ {{\rm{s}}}^{-1}$ . in an archival 2005 xmm-newton exposure, we measured a spin period of ∼3.3 s, indicating a secular spin-up of ${\dot{p}}_{\sec }\simeq -{10}^{-9}\,{\rm{s}}\ {{\rm{s}}}^{-1}$ , a value in the range of other known pulxs. our findings suggest that the system consists of a massive donor, possibly an ob giant or supergiant, and a moderately magnetic (dipole field component in the range 1012 g $\lesssim {b}_{\mathrm{dip}}\lesssim {10}^{13}$ g) accreting ns with weakly beamed emission ( $1/12\lesssim b\lesssim 1/4$ ). | discovery of a 2.8 s pulsar in a 2 day orbit high-mass x-ray binary powering the ultraluminous x-ray source ulx-7 in m51 |
we study the distribution of cold dark matter (cdm) in cosmological simulations from the fire (feedback in realistic environments) project, for m* ∼ 104-11 m⊙ galaxies in mh ∼ 109-12 m⊙ haloes. fire incorporates explicit stellar feedback in the multiphase interstellar medium, with energetics from stellar population models. we find that stellar feedback, without `fine-tuned' parameters, greatly alleviates small-scale problems in cdm. feedback causes bursts of star formation and outflows, altering the dm distribution. as a result, the inner slope of the dm halo profile (α) shows a strong mass dependence: profiles are shallow at mh ∼ 1010-1011 m⊙ and steepen at higher/lower masses. the resulting core sizes and slopes are consistent with observations. this is broadly consistent with previous work using simpler feedback schemes, but we find steeper mass dependence of α, and relatively late growth of cores. because the star formation efficiency m*/mh is strongly halo mass dependent, a rapid change in α occurs around mh ∼ 1010 m⊙ (m* ∼ 106-107 m⊙), as sufficient feedback energy becomes available to perturb the dm. large cores are not established during the period of rapid growth of haloes because of ongoing dm mass accumulation. instead, cores require several bursts of star formation after the rapid build-up has completed. stellar feedback dramatically reduces circular velocities in the inner kpc of massive dwarfs; this could be sufficient to explain the `too big to fail' problem without invoking non-standard dm. finally, feedback and baryonic contraction in milky way-mass haloes produce dm profiles slightly shallower than the navarro-frenk-white profile, consistent with the normalization of the observed tully-fisher relation. | the impact of baryonic physics on the structure of dark matter haloes: the view from the fire cosmological simulations |
supermassive black holes (smbhs) that reside at the centres of galaxies can inject vast amounts of energy into the surrounding gas and are thought to be a viable mechanism to quench star formation in massive galaxies. here, we study the $10^{9-12.5}\, \mathrm{m_\odot }$ stellar mass central galaxy population of the illustristng simulation, specifically the tng100 and tng300 volumes at z = 0, and show how the three components - smbh, galaxy, and circumgalactic medium (cgm) - are interconnected in their evolution. we find that gas entropy is a sensitive diagnostic of feedback injection. in particular, we demonstrate how the onset of the low-accretion black hole (bh) feedback mode, realized in the illustristng model as a kinetic, bh-driven wind, leads not only to star formation quenching at stellar masses $\gtrsim 10^{10.5}\, \mathrm{m_\odot }$ but also to a change in thermodynamic properties of the (non-star-forming) gas, both within the galaxy and beyond. the illustristng kinetic feedback from smbhs increases the average gas entropy, within the galaxy and in the cgm, lengthening typical gas cooling times from $10\!-\!100\, \mathrm{myr}$ to $1\!-\!10\, \mathrm{gyr}$, effectively ceasing ongoing star formation and inhibiting radiative cooling and future gas accretion. in practice, the same active galactic nucleus (agn) feedback channel is simultaneously 'ejective' and 'preventative' and leaves an imprint on the temperature, density, entropy, and cooling times also in the outer reaches of the gas halo, up to distances of several hundred kiloparsecs. in the illustristng model, a long-lasting quenching state can occur for a heterogeneous cgm, whereby the hot and dilute cgm gas of quiescent galaxies contains regions of low-entropy gas with short cooling times. | ejective and preventative: the illustristng black hole feedback and its effects on the thermodynamics of the gas within and around galaxies |
the first observation of a binary neutron star (ns) coalescence by the advanced ligo and advanced virgo gravitational-wave (gw) detectors offers an unprecedented opportunity to study matter under the most extreme conditions. after such a merger, a compact remnant is left over whose nature depends primarily on the masses of the inspiraling objects and on the equation of state of nuclear matter. this could be either a black hole (bh) or an ns, with the latter being either long-lived or too massive for stability implying delayed collapse to a bh. here, we present a search for gws from the remnant of the binary ns merger gw170817 using data from advanced ligo and advanced virgo. we search for short- (≲1 s) and intermediate-duration (≲500 s) signals, which include gw emission from a hypermassive ns or supramassive ns, respectively. we find no signal from the post-merger remnant. our derived strain upper limits are more than an order of magnitude larger than those predicted by most models. for short signals, our best upper limit on the root sum square of the gw strain emitted from 1-4 khz is {h}{rss}50 % =2.1× {10}-22 {{hz}}-1/2 at 50% detection efficiency. for intermediate-duration signals, our best upper limit at 50% detection efficiency is {h}{rss}50 % =8.4× {10}-22 {{hz}}-1/2 for a millisecond magnetar model, and {h}{rss}50 % =5.9× {10}-22 {{hz}}-1/2 for a bar-mode model. these results indicate that post-merger emission from a similar event may be detectable when advanced detectors reach design sensitivity or with next-generation detectors. | search for post-merger gravitational waves from the remnant of the binary neutron star merger gw170817 |
we present the determination of stellar parameters and individual elemental abundances for 6 million stars from ∼8 million low-resolution (r ∼ 1800) spectra from lamost dr5. this is based on a modeling approach that we dub the data-driven payne (dd-payne), which inherits essential ingredients from both the payne and the cannon. it is a data-driven model that incorporates constraints from theoretical spectral models to ensure the derived abundance estimates are physically sensible. stars in lamost dr5 that are in common with either galah dr2 or apogee dr14 are used to train a model that delivers stellar parameters (t eff, log g, v mic) and abundances for 16 elements (c, n, o, na, mg, al, si, ca, ti, cr, mn, fe, co, ni, cu, and ba) over a metallicity range of -4 dex < [fe/h] < 0.6 dex when applied to the lamost spectra. cross-validation and repeat observations suggest that, for s/npixel ≥ 50, the typical internal abundance precision is 0.03-0.1 dex for the majority of these elements, with 0.2-0.3 dex for cu and ba, and the internal precision of t eff and log g is better than 30 k and 0.07 dex, respectively. abundance systematics at the ∼0.1 dex level are present in these estimates but are inherited from the high-resolution surveys’ training labels. for some elements, galah provides more robust training labels, for others, apogee. we provide flags to guide the quality of the label determination and identify binary/multiple stars in lamost dr5. an electronic version of the abundance catalog is made publicly available.12 | abundance estimates for 16 elements in 6 million stars from lamost dr5 low-resolution spectra |
the deep underground neutrino experiment (dune), a 40-kton underground liquid argon time projection chamber experiment, will be sensitive to the electron-neutrino flavor component of the burst of neutrinos expected from the next galactic core-collapse supernova. such an observation will bring unique insight into the astrophysics of core collapse as well as into the properties of neutrinos. the general capabilities of dune for neutrino detection in the relevant few- to few-tens-of-mev neutrino energy range will be described. as an example, dune's ability to constrain the νe spectral parameters of the neutrino burst will be considered. | supernova neutrino burst detection with the deep underground neutrino experiment |
measurements of the atmospheric carbon (c) and oxygen (o) relative to hydrogen (h) in hot jupiters (relative to their host stars) provide insight into their formation location and subsequent orbital migration1,2. hot jupiters that form beyond the major volatile (h2o/co/co2) ice lines and subsequently migrate post disk-dissipation are predicted have atmospheric carbon-to-oxygen ratios (c/o) near 1 and subsolar metallicities2, whereas planets that migrate through the disk before dissipation are predicted to be heavily polluted by infalling o-rich icy planetesimals, resulting in c/o < 0.5 and super-solar metallicities1,2. previous observations of hot jupiters have been able to provide bounded constraints on either h2o (refs. 3-5) or co (refs. 6,7), but not both for the same planet, leaving uncertain4 the true elemental c and o inventory and subsequent c/o and metallicity determinations. here we report spectroscopic observations of a typical transiting hot jupiter, wasp-77ab. from these, we determine the atmospheric gas volume mixing ratio constraints on both h2o and co (9.5 × 10−5-1.5 × 10−4 and 1.2 × 10−4-2.6 × 10−4, respectively). from these bounded constraints, we are able to derive the atmospheric c/h (0.35−0.10+0.17? × solar) and o/h (0.32−0.08+0.12? × solar) abundances and the corresponding atmospheric carbon-to-oxygen ratio (c/o = 0.59 ± 0.08; the solar value is 0.55). the sub-solar (c+o)/h (0.33−0.09+0.13? × solar) is suggestive of a metal-depleted atmosphere relative to what is expected for jovian-like planets1 while the near solar value of c/o rules out the disk-free migration/c-rich2 atmosphere scenario. | a solar c/o and sub-solar metallicity in a hot jupiter atmosphere |
we report the discovery of four galaxy candidates observed 450-600 myr after the big bang with photometric redshifts between z ~ 8.3 and 10.2 measured using james webb space telescope (jwst) nircam imaging of the galaxy cluster whl0137-08 observed in eight filters spanning 0.8-5.0 μm, plus nine hubble space telescope filters spanning 0.4-1.7 μm. one candidate is gravitationally lensed with a magnification of μ ~ 8, while the other three are located in a nearby nircam module with expected magnifications of μ ≲ 1.1. using sed fitting, we estimate the stellar masses of these galaxies are typically in the range $\mathrm{log}{m}_{\star }/{m}_{\odot }$ = 8.3-8.7. all appear young, with mass-weighted ages <240 myr, low dust content av< 0.15 mag, and specific star formation rates ssfr ~0.25-10 gyr-1 for most. one z ~ 9 candidate is consistent with an age <5 myr and an ssfr ~10 gyr-1, as inferred from a strong f444w excess, implying [o iii ]+h β rest-frame equivalent width ~2000 å, although an older z ~ 10 object is also allowed. another z ~ 9 candidate is lensed into an arc 2.″4 long with a magnification of μ ~ 8. this arc is the most spatially resolved galaxy at z ~ 9 known to date, revealing structures ~30 pc across. follow-up spectroscopy of whl0137-08 with jwst/nirspec will be useful to spectroscopically confirm these high-redshift galaxy candidates and to study their physical properties in more detail. | high-redshift galaxy candidates at z = 9-10 as revealed by jwst observations of whl0137-08 |
within the next few years, advanced ligo and virgo should detect gravitational waves from binary neutron star and neutron star-black hole mergers. these sources are also predicted to power a broad array of electromagnetic transients. because the electromagnetic signatures can be faint and fade rapidly, observing them hinges on rapidly inferring the sky location from the gravitational-wave observations. markov chain monte carlo methods for gravitational-wave parameter estimation can take hours or more. we introduce bayestar, a rapid, bayesian, non-markov chain monte carlo sky localization algorithm that takes just seconds to produce probability sky maps that are comparable in accuracy to the full analysis. prompt localizations from bayestar will make it possible to search electromagnetic counterparts of compact binary mergers. | rapid bayesian position reconstruction for gravitational-wave transients |
we present the payne, a general method for the precise and simultaneous determination of numerous stellar labels from observed spectra, based on fitting physical spectral models. the payne combines a number of important methodological aspects: it exploits the information from much of the available spectral range; it fits all labels (stellar parameters and elemental abundances) simultaneously; it uses spectral models, where the structure of the atmosphere and the radiative transport are consistently calculated to reflect the stellar labels. at its core the payne has an approach to accurate and precise interpolation and prediction of the spectrum in high-dimensional label space that is flexible and robust, yet based on only a moderate number of ab initio models ({ \mathcal o }(1000) for 25 labels). with a simple neural-net-like functional form and a suitable choice of training labels, this interpolation yields a spectral flux prediction good to 10-3 rms across a wide range of t eff and {log}g (including dwarfs and giants). we illustrate the power of this approach by applying it to the apogee dr14 data set, drawing on kurucz models with recently improved line lists: without recalibration, we obtain physically sensible stellar parameters as well as 15 elemental abundances that appear to be more precise than the published apogee dr14 values. in short, the payne is an approach that for the first time combines all these key ingredients, necessary for progress toward optimal modeling of survey spectra; and it leads to both precise and accurate estimates of stellar labels, based on physical models and without “recalibration.” both the codes and catalog are made publicly available online. | the payne: self-consistent ab initio fitting of stellar spectra |
vector vortex beams are conventionally created as the superposition of orbital angular momentum (oam) modes with orthogonal polarizations, limiting the available degrees of freedom (dofs) to 2, while their creation by complex optical devices such as metasurfaces, liquid crystals, and interferometers has hindered their versatility. here we demonstrate a new class of vector vortex beam constructed from four dofs as multiple ray-like trajectories with wave-like properties, which we create by operating a simple anisotropic microchip laser in a frequency-degenerate state. our new structure is obtained by the superposition of two stable periodic ray trajectories, simultaneously fulfilling a completed oscillation in the cavity. by a simple external modulation, we can transform our ray trajectories into vortex beams with large oam, multiple singularities, as well as exotic helical star-shaped patterns. our experimental results are complemented by a complete theoretical framework for this new class of beam, revealing parallels to hybrid su(2) coherent states. our approach offers in principle unlimited dofs for vectorial structured light with concomitant applications, for example, in engineering classically entangled light and in vectorial optical trapping and tweezing. | structured ray-wave vector vortex beams in multiple degrees of freedom from a laser |
cosmic dawn ii (coda ii) is a new, fully coupled radiation-hydrodynamics simulation of cosmic reionization and galaxy formation and their mutual impact, to redshift z < 6. with 40963 particles and cells in a 94 mpc box, it is large enough to model global reionization and its feedback on galaxy formation while resolving all haloes above 108 m⊙. using the same hybrid cpu-gpu code ramses-cudaton as coda i in ocvirk et al. (2016), coda ii modified and re-calibrated the subgrid star formation algorithm, making reionization end earlier, at z ≳ 6, thereby better matching the observations of intergalactic lyman α opacity from quasar spectra and electron-scattering optical depth from cosmic microwave background fluctuations. coda ii predicts a uv continuum luminosity function in good agreement with observations of high-z galaxies, especially at z = 6. as in coda i, reionization feedback suppresses star formation in haloes below ∼2 × 109 m⊙, though suppression here is less severe, a possible consequence of modifying the star formation algorithm. suppression is environment dependent, occurring earlier (later) in overdense (underdense) regions, in response to their local reionization times. using a constrained realization of lambda cold dark matter constructed from galaxy survey data to reproduce the large-scale structure and major objects of the present-day local universe, coda ii serves to model both global and local reionization. in coda ii, the milky way and m31 appear as individual islands of reionization, i.e. they were not reionized by the progenitor of the virgo cluster, or by nearby groups, or by each other. | cosmic dawn ii (coda ii): a new radiation-hydrodynamics simulation of the self-consistent coupling of galaxy formation and reionization |
there is now strong evidence that the close binary fraction (p < 104 days; a < 10 au) of solar-type stars (m 1 ≈ 0.6-1.5 {m}⊙ ) decreases significantly with metallicity. although early surveys showed that the observed spectroscopic binary (sb) fractions in the galactic disk and halo are similar (e.g., carney-latham sample), these studies did not correct for incompleteness. in this study, we examine five different surveys and thoroughly account for their underlying selection biases to measure the intrinsic occurrence rate of close solar-type binaries. we reanalyze (1) a volume-limited sample of solar-type stars, (2) the carney-latham sb survey of high proper motion stars, (3) various sb samples of metal-poor giants, (4) the apogee survey of radial velocity (rv) variables, and (5) eclipsing binaries (ebs) discovered by kepler. the observed apogee rv variability fraction and kepler eb fraction both decrease by a factor of ≈4 across -1.0 < [fe/h] < 0.5 at the 22σ and 9σ confidence levels, respectively. after correcting for incompleteness, all five samples/methods exhibit a quantitatively consistent anticorrelation between the intrinsic close binary fraction (a < 10 au) and metallicity: f close = 53% ± 12%, 40% ± 6%, 24% ± 4%, and 10% ± 3% at [fe/h] = -3.0, -1.0, -0.2 (mean field metallicity), and +0.5, respectively. we present simple fragmentation models that explain why the close binary fraction of solar-type stars strongly decreases with metallicity while the wide binary fraction, close binary fraction of ob stars, and initial mass function are all relatively constant across -1.5 ≲ [fe/h] < 0.5. the majority of solar-type stars with [fe/h] ≲ -1.0 will interact with a stellar companion, which has profound implications for binary evolution in old and metal-poor environments such as the galactic halo, bulge, thick disk, globular clusters, dwarf galaxies, and high-redshift universe. | the close binary fraction of solar-type stars is strongly anticorrelated with metallicity |
using simulations performed with the population synthesis code uc(mobse), we compute the merger rate densities and detection rates of compact binary mergers formed in isolation for second- and third-generation gravitational wave detectors. we estimate how rates are affected by uncertainties on key stellar physics parameters, namely common envelope evolution and natal kicks. we estimate how future upgrades will increase the size of the available catalog of merger events, and we discuss features of the merger rate density that will become accessible with third-generation detectors. | gravitational-wave detection rates for compact binaries formed in isolation: ligo/virgo o3 and beyond |
we present the atacama large millimeter/submillimeter array detection of the [o iii] 88 μm line and rest-frame 90 μm dust continuum emission in a y-dropout lyman break galaxy (lbg), macs0416_y1 lying behind the frontier field cluster macs j0416.1-2403. this [o iii] detection confirms the lbg with a spectroscopic redshift of z = 8.3118 ± 0.0003, making this object one of the farthest galaxies ever identified spectroscopically. the observed 850 μm flux density of 137 ± 26 μjy corresponds to a de-lensed total infrared (ir) luminosity of {l}ir}=(1.7+/- 0.3)× {10}11 {l}⊙if assuming a dust temperature of t dust = 50 k and an emissivity index of β = 1.5, yielding a large dust mass of 4× {10}6{m}⊙ . the ultraviolet-to-far-ir spectral energy distribution modeling where the [o iii] emissivity model is incorporated suggests the presence of a young (τ age ≈ 4 myr), star-forming ({sfr}≈ 60 {m}⊙yr-1), moderately metal-polluted (z ≈ 0.2z ⊙) stellar component with a mass of m star = 3 × 108 m ⊙. an analytic dust mass evolution model with a single episode of star formation does not reproduce the metallicity and dust mass in τ age ≈ 4 myr, suggesting a pre-existing evolved stellar component with m star ∼ 3 × 109 m ⊙ and τ age ∼ 0.3 gyr as the origin of the dust mass. | detection of the far-infrared [o iii] and dust emission in a galaxy at redshift 8.312: early metal enrichment in the heart of the reionization era |
stars in the immediate vicinity of supermassive black holes (smbhs) can be ripped apart by the tidal forces of the black hole. the subsequent accretion of the stellar material causes a spectacular flare of electromagnetic radiation. here, we provide a review of the observations of tidal disruption events (tdes), with an emphasis on the important contributions of swift to this field. tdes represent a new probe of matter under strong gravity, and have opened up a new window into studying accretion physics under extreme conditions. the events probe relativistic effects, provide a new means of measuring black hole spin, and represent signposts of intermediate-mass bhs, binary bhs and recoiling bhs. luminous, high-amplitude x-ray flares, matching key predictions of the tidal disruption scenario, have first been discovered with rosat, and more recently with other missions and in other wavebands. the swift discovery of two γ-ray emitting, jetted tdes, never seen before, has provided us with a unique probe of the early phases of jet formation and evolution, and swift j1644+75 has the best covered lightcurve of any tde to date. further, swift has made important contributions in providing well-covered lightcurves of tdes discovered with other instruments, setting constraints on the physics that govern the tde evolution, and including the discovery of the first candidate binary smbh identified from a tde lightcurve. in x-rays, tdes probe relativistic effects (via emission-line profiles or precession effects in the kerr metric) and the extremes of accretion physics at high rates and near the last stable orbit, and provide us with a new means of measuring bh spin. jetted tdes provide new insight into the formation and early evolution of radio jets, and may shed new light on related issues like the cause of the radio-loud radio-quiet dichotomy of active galactic nuclei (agn). tdes, once detected in large numbers, will unveil the population of imbhs in the universe. tde rates depend on, and therefore trace, stellar dynamics in galaxy cores on spatial scales which cannot be resolved directly. tdes are signposts of binary smbhs and recoiling bhs, because their rates are strongly enhanced under these conditions, and tdes will occur off-nuclear if the smbh is recoiling. tdes in gas-rich environments will illuminate the circum-nuclear material, so that the reprocessed emission lines and their temporal evolution provide us with an unparalleled opportunity of reverberation mapping the cores of quiescent galaxies. here, we present an overview of the status of observations of tdes, highlighting the important role plaid by the swift mission (gehrels et al., 2004; gehrels and cannizzo, in press). an accompanying review by lodato (in press) will focus on theoretical aspects of tidal disruption. | tidal disruption of stars by supermassive black holes: status of observations |
the cores of neutron stars (nss) near the maximum mass can realize a transitional change to quark matter (qm). gravitational waves from binary ns mergers are expected to convey information about the equation of state (eos) sensitive to the qm transition. here, we present the first results of gravitational wave simulation with the realistic eos that is consistent with ab initio approaches of χ eft and pqcd and is assumed to go through smooth crossover. we compare them to results obtained with another eos with a first-order hadron-quark phase transition. our results suggest that early collapse to a black hole in the post-merger stage after ns merger robustly signifies softening of the eos associated with the qm onset in the crossover scenario. the nature of the hadron-quark phase transition can be further constrained by the condition that electromagnetic counterparts should be energized by the material left outside the remnant black hole. | gravitational wave signal for quark matter with realistic phase transition |
we present the occurrence rates for rocky planets in the habitable zones (hzs) of main-sequence dwarf stars based on the kepler dr25 planet candidate catalog and gaia-based stellar properties. we provide the first analysis in terms of star-dependent instellation flux, which allows us to track hz planets. we define η⊕ as the hz occurrence of planets with radii between 0.5 and 1.5 r⊕ orbiting stars with effective temperatures between 4800 and 6300 k. we find that η⊕ for the conservative hz is between ${0.37}_{-0.21}^{+0.48}$ (errors reflect 68% credible intervals) and ${0.60}_{-0.36}^{+0.90}$ planets per star, while the optimistic hz occurrence is between ${0.58}_{-0.33}^{+0.73}$ and ${0.88}_{-0.51}^{+1.28}$ planets per star. these bounds reflect two extreme assumptions about the extrapolation of completeness beyond orbital periods where dr25 completeness data are available. the large uncertainties are due to the small number of detected small hz planets. we find similar occurrence rates between using poisson likelihood bayesian analysis and using approximate bayesian computation. our results are corrected for catalog completeness and reliability. both completeness and the planet occurrence rate are dependent on stellar effective temperature. we also present occurrence rates for various stellar populations and planet size ranges. we estimate with 95% confidence that, on average, the nearest hz planet around g and k dwarfs is ∼6 pc away and there are ∼4 hz rocky planets around g and k dwarfs within 10 pc of the sun. | the occurrence of rocky habitable-zone planets around solar-like stars from kepler data |
a luminous radio burst was recently detected in temporal coincidence with a hard x-ray flare from the galactic magnetar sgr 1935+2154 with a time and frequency structure consistent with cosmological fast radio bursts (frbs) and a fluence within a factor of ≲10 of the least energetic extragalactic frb previously detected. although active magnetars are commonly invoked frb sources, several distinct mechanisms have been proposed for generating the radio emission that make different predictions for the accompanying higher-frequency radiation. we show that the properties of the coincident radio and x-ray flares from sgr 1935+2154, including their approximate simultaneity and relative fluence ${e}_{\mathrm{radio}}/{e}_{{\rm{x}}}\sim {10}^{-5}$ , as well as the duration and spectrum of the x-ray emission, are consistent with extant predictions for the synchrotron maser shock model. rather than arising from the inner magnetosphere, the x-rays are generated by (incoherent) synchrotron radiation from thermal electrons heated at the same internal shocks that produce the coherent maser emission as ultrarelativistic flare ejecta collides with a slower particle outflow (e.g., as generated by earlier flaring activity) on a radial scale of $\sim {10}^{11}$ cm. although the rate of sgr 1935+2154-like bursts in the local universe is not sufficient to contribute appreciably to the extragalactic frb rate, the inclusion of an additional population of more active magnetars with stronger magnetic fields than the galactic population can explain both the frb rate and the repeating fraction, but only if the population of active magnetars are born at a rate that is at least 2 orders of magnitude lower than that of the sgr 1935+2154-like magnetars. this may imply that the more active magnetar sources are not younger magnetars formed in a similar way to the milky way population (e.g., via ordinary supernovae) but are instead formed through more exotic channels, such as superluminous supernovae, accretion-induced collapse, or neutron star mergers. | implications of a fast radio burst from a galactic magnetar |
detections and non-detections of lyman alpha (lyα) emission from z > 6 galaxies (<1 gyr after the big bang) can be used to measure the timeline of cosmic reionization. of key interest to measuring reionization's mid-stages, but also increasing observational challenge, are observations at z > 7, where lyα redshifts to near infra-red wavelengths. here we present a search for z > 7.2 lyα emission in 53 intrinsically faint lyman break galaxy candidates, gravitationally lensed by massive galaxy clusters, in the kmos lens-amplified spectroscopic survey (klass). with integration times of ∼7-10 h, we detect no lyα emission with signal-to-noise ratio (s/n) > 5 in our sample. we determine our observations to be 80 per cent complete for 5σ spatially and spectrally unresolved emission lines with integrated line flux >5.7 × 10-18 erg s-1 cm-2. we define a photometrically selected sub-sample of 29 targets at z = 7.9 ± 0.6, with a median 5σ lyα ew limit of 58 å. we perform a bayesian inference of the average intergalactic medium (igm) neutral hydrogen fraction using their spectra. our inference accounts for the wavelength sensitivity and incomplete redshift coverage of our observations, and the photometric redshift probability distribution of each target. these observations, combined with samples from the literature, enable us to place a lower limit on the average igm neutral hydrogen fraction of > 0.76 (68{{ per cent}}), > 0.46 (95{{ per cent}}) at z ∼ 8, providing further evidence of rapid reionization at z ∼ 6-8. we show that this is consistent with reionization history models extending the galaxy luminosity function to m_{uv}≲ -12, with low ionizing photon escape fractions, f_{esc} ≲ 15{{ per cent}}. | inferences on the timeline of reionization at z ∼ 8 from the kmos lens-amplified spectroscopic survey |
type-i x-ray bursts arise from unstable thermonuclear burning of accreted fuel on the surface of neutron stars. in this chapter we review the fundamental physics of the burning processes, and summarise the observational, numerical, and nuclear experimental progress over the preceding decade. we describe the current understanding of the conditions that lead to burst ignition, and the influence of the burst fuel on the observational characteristics. we provide an overview of the processes which shape the burst x-ray spectrum, including the observationally elusive discrete spectral features. we report on the studies of timing behaviour related to nuclear burning, including burst oscillations and mhz quasi-periodic oscillations. we describe the increasing role of nuclear experimental physics in the interpretation of astrophysical data and models. we survey the simulation projects that have taken place to date, and chart the increasing dialogue between modellers, observers, and nuclear experimentalists. finally, we identify some open problems with prospects of a resolution within the timescale of the next such review. | thermonuclear x-ray bursts |
galsim is a collaborative, open-source project aimed at providing an image simulation tool of enduring benefit to the astronomical community. it provides a software library for generating images of astronomical objects such as stars and galaxies in a variety of ways, efficiently handling image transformations and operations such as convolution and rendering at high precision. we describe the galsim software and its capabilities, including necessary theoretical background. we demonstrate that the performance of galsim meets the stringent requirements of high precision image analysis applications such as weak gravitational lensing, for current datasets and for the stage iv dark energy surveys of the large synoptic survey telescope, esa's euclid mission, and nasa's wfirst-afta mission. the galsim project repository is public and includes the full code history, all open and closed issues, installation instructions, documentation, and wiki pages (including a frequently asked questions section). the galsim repository can be found at https://github.com/galsim-developers/galsim. | galsim: the modular galaxy image simulation toolkit |
in this brief communication we provide the rationale for and the outcome of the international astronomical union (iau) resolution vote at the xxixth general assembly in honolulu, hawaii, in 2015, on recommended nominal conversion constants for selected solar and planetary properties. the problem addressed by the resolution is a lack of established conversion constants between solar and planetary values and si units: a missing standard has caused a proliferation of solar values (e.g., solar radius, solar irradiance, solar luminosity, solar effective temperature, and solar mass parameter) in the literature, with cited solar values typically based on best estimates at the time of paper writing. as precision of observations increases, a set of consistent values becomes increasingly important. to address this, an iau working group on nominal units for stellar and planetary astronomy formed in 2011, uniting experts from the solar, stellar, planetary, exoplanetary, and fundamental astronomy, as well as from general standards fields to converge on optimal values for nominal conversion constants. the effort resulted in the iau 2015 resolution b3, passed at the iau general assembly by a large majority. the resolution recommends the use of nominal solar and planetary values, which are by definition exact and are expressed in si units. these nominal values should be understood as conversion factors only, not as the true solar/planetary properties or current best estimates. authors and journal editors are urged to join in using the standard values set forth by this resolution in future work and publications to help minimize further confusion. | nominal values for selected solar and planetary quantities: iau 2015 resolution b3 |
the radio-emitting neutron star population encompasses objects with spin periods ranging from milliseconds to tens of seconds. as they age and spin more slowly, their radio emission is expected to cease. we present the discovery of an ultra-long-period radio-emitting neutron star, psr j0901-4046, with spin properties distinct from the known spin- and magnetic-decay-powered neutron stars. with a spin period of 75.88 s, a characteristic age of 5.3 myr and a narrow pulse duty cycle, it is uncertain how its radio emission is generated and challenges our current understanding of how these systems evolve. the radio emission has unique spectro-temporal properties, such as quasi-periodicity and partial nulling, that provide important clues to the emission mechanism. detecting similar sources is observationally challenging, which implies a larger undetected population. our discovery establishes the existence of ultra-long-period neutron stars, suggesting a possible connection to the evolution of highly magnetized neutron stars, ultra-long-period magnetars and fast radio bursts. | discovery of a radio-emitting neutron star with an ultra-long spin period of 76 s |
gravitational waves from the coalescence of two neutron stars were recently detected for the first time by the ligo-virgo collaboration, in event gw170817. this detection placed an upper limit on the effective tidal deformability of the two neutron stars and tightly constrained the chirp mass of the system. we report here on a new simplification that arises in the effective tidal deformability of the binary, when the chirp mass is specified. we find that, in this case, the effective tidal deformability of the binary is surprisingly independent of the component masses of the individual neutron stars, and instead depends primarily on the ratio of the chirp mass to the neutron star radius. thus, a measurement of the effective tidal deformability can be used to directly measure the neutron star radius. we find that the upper limit on the effective tidal deformability from gw170817 implies that the radius cannot be larger than ∼13 km, at the 90% level, independent of the assumed masses for the component stars. the result can be applied generally, to probe the stellar radii in any neutron star-neutron star merger with a measured chirp mass. the approximate mass independence disappears for neutron star-black hole mergers. finally, we discuss a bayesian inference of the equation of state that uses the measured chirp mass and tidal deformability from gw170817 combined with nuclear and astrophysical priors and discuss possible statistical biases in this inference. | tidal deformability from gw170817 as a direct probe of the neutron star radius |
we consider a solution of the effective four-dimensional einstein equations, obtained from the general relativistic schwarzschild metric through the principle of minimal geometric deformation (mgd). since the brane tension can, in general, introduce new singularities on a relativistic eötvös brane model in the mgd framework, we require the absence of observed singularities, in order to constrain the brane tension. we then study the corresponding bose-einstein condensate (bec) gravitational system and determine the critical stability region of bec mgd stellar configurations. finally, the critical stellar densities are shown to be related with critical points of the information entropy. | stability of the graviton bose-einstein condensate in the brane-world |
binary neutron star mergers are promising sources of gravitational waves for ground-based detectors such as advanced ligo. neutron-rich material ejected by these mergers may also be the main source of r-process elements in the universe, while radioactive decays in the ejecta can power bright electromagnetic postmerger signals. neutrino-matter interactions play a critical role in the evolution of the composition of the ejected material, which significantly impacts the outcome of nucleosynthesis and the properties of the associated electromagnetic signal. in this work, we present a simulation of a binary neutron star merger using an improved method for estimating the average neutrino energies in our energy-integrated neutrino transport scheme. these energy estimates are obtained by evolving the neutrino number density in addition to the neutrino energy and flux densities. we show that significant changes are observed in the composition of the polar ejecta when comparing our new results with earlier simulations in which the neutrino spectrum was assumed to be the same everywhere in optically thin regions. in particular, we find that material ejected in the polar regions is less neutron rich than previously estimated. our new estimates of the composition of the polar ejecta make it more likely that the color and time scale of the electromagnetic signal depend on the orientation of the binary with respect to an observer's line of sight. these results also indicate that important observable properties of neutron star mergers are sensitive to the neutrino energy spectrum, and may need to be studied through simulations including a more accurate, energy-dependent neutrino transport scheme. | impact of an improved neutrino energy estimate on outflows in neutron star merger simulations |
rates of stellar tidal disruption events (tdes) by supermassive black holes (smbhs) due to two-body relaxation are calculated using a large galaxy sample (n ≈ 200) in order to explore the sensitivity of the tde rates to observational uncertainties, such as the parametrization of galaxy light profiles and the stellar mass function. the largest uncertainty arises due to the poorly constrained occupation fraction of smbhs in low-mass galaxies, which otherwise dominate the total tde rate. the detection rate of tde flares by optical surveys is calculated as a function of smbh mass and other observables for several physically motivated models of tde emission. we also quantify the fraction of galaxies that produce deeply penetrating disruption events. if the majority of the detected events are characterized by super-eddington luminosities (such as disc winds, or synchrotron radiation from an off-axis relativistic jet), then the measured smbh mass distribution will tightly constrain the low-end smbh occupation fraction. if eddington-limited emission channels dominate, however, then the occupation fraction sensitivity is much less pronounced in a flux-limited survey (although still present in a volume-complete event sample). the smbh mass distribution of the current sample of tdes, though highly inhomogeneous and encumbered by selection effects, already suggests that eddington-limited emission channels dominate. even our most conservative rate estimates appear to be in tension with much lower observationally inferred tde rates, and we discuss several possible resolutions to this discrepancy. | rates of stellar tidal disruption as probes of the supermassive black hole mass function |
the observation of a compact object with a mass of 2.50-2.67m⊙ on 2019 august 14, by the ligo scientific and virgo collaborations (lvc) has the potential to improve our understanding of the supranuclear equation of state. while the gravitational-wave analysis of the lvc suggests that gw190814 likely was a binary black hole system, the secondary component could also have been the heaviest neutron star observed to date. we use our previously derived nuclear-physics-multimessenger astrophysics framework to address the nature of this object. based on our findings, we determine gw190814 to be a binary black hole merger with a probability of >99.9%. even if we weaken previously employed constraints on the maximum mass of neutron stars, the probability of a binary black hole origin is still ∼81%. furthermore, we study the impact that this observation has on our understanding of the nuclear equation of state by analyzing the allowed region in the mass-radius diagram of neutron stars for both a binary black hole or neutron star-black hole scenario. we find that the unlikely scenario in which the secondary object was a neutron star requires rather stiff equations of state with a maximum speed of sound ${c}_{s}\geqslant \sqrt{0.6}$ times the speed of light, while the binary black hole scenario does not offer any new insight. | on the nature of gw190814 and its impact on the understanding of supranuclear matter |
the bulk of cosmic matter resides in a dilute reservoir that fills the space between galaxies, the intergalactic medium (igm). the history of this reservoir is intimately tied to the cosmic histories of structure formation, star formation, and supermassive black hole accretion. our models for the igm at intermediate redshifts (2≲z≲5) are a tremendous success, quantitatively explaining the statistics of lyα absorption of intergalactic hydrogen. however, at both lower and higher redshifts (and around galaxies) much is still unknown about the igm. we review the theoretical models and measurements that form the basis for the modern understanding of the igm, and we discuss unsolved puzzles (ranging from the largely unconstrained process of reionization at high z to the missing baryon problem at low z), highlighting the efforts that have the potential to solve them. | the evolution of the intergalactic medium |
we study the impact of mass-transfer physics on the observable properties of binary black hole populations that formed through isolated binary evolution. we used the posydon framework to combine detailed mesa binary simulations with the cosmic population synthesis tool to obtain an accurate estimate of merging binary black hole observables with a specific focus on the spins of the black holes. we investigate the impact of mass-accretion efficiency onto compact objects and common-envelope efficiency on the observed distributions of the effective inspiral spin parameter χeff, chirp mass mchirp, and binary mass ratio q. we find that low common envelope efficiency translates to tighter orbits following the common envelope and therefore more tidally spun up second-born black holes. however, these systems have short merger timescales and are only marginally detectable by current gravitational-wave detectors as they form and merge at high redshifts (z ∼ 2), outside current detector horizons. assuming eddington-limited accretion efficiency and that the first-born black hole is formed with a negligible spin, we find that all non-zero χeff systems in the detectable population can come only from the common envelope channel as the stable mass-transfer channel cannot shrink the orbits enough for efficient tidal spin-up to take place. we find that the local rate density (z ≃ 0.01) for the common envelope channel is in the range of ∼17-113 gpc−3 yr−1, considering a range of αce ∈ [0.2, 5.0], while for the stable mass transfer channel the rate density is ∼25 gpc−3 yr−1. the latter drops by two orders of magnitude if the mass accretion onto the black hole is not eddington limited because conservative mass transfer does not shrink the orbit as efficiently as non-conservative mass transfer does. finally, using gwtc-2 events, we constrained the lower bound of branching fraction from other formation channels in the detected population to be ∼0.2. assuming all remaining events to be formed through either stable mass transfer or common envelope channels, we find moderate to strong evidence in favour of models with inefficient common envelopes. | the impact of mass-transfer physics on the observable properties of field binary black hole populations |
we present a novel analytic framework to model the steady-state structure of multiphase galactic winds comprised of a hot, volume-filling component and a cold, clumpy component. we first derive general expressions for the structure of the hot phase for arbitrary mass, momentum, and energy source terms. next, informed by recent simulations, we parameterize the cloud-wind mass transfer rates, which are set by the competition between turbulent mixing and radiative cooling. this enables us to cast the cloud-wind interaction as a source term for the hot phase and thereby simultaneously solve for the evolution of both phases, fully accounting for their bidirectional influence. with this model, we explore the nature of galactic winds over a broad range of conditions. we find that (i) with realistic parameter choices, we naturally produce a hot, low-density wind that transports energy while entraining a significant flux of cold clouds, (ii) mixing dominates the cold cloud acceleration and decelerates the hot wind, (iii) during mixing thermalization of relative kinetic energy provides significant heating, (iv) systems with low hot phase mass loading factors and/or star formation rates can sustain higher initial cold phase mass loading factors, but the clouds are quickly shredded, and (v) systems with large hot phase mass loading factors and/or high star formation rates cannot sustain large initial cold phase mass loading factors, but the clouds tend to grow with distance from the galaxy. our results highlight the necessity of accounting for the multiphase structure of galactic winds, both physically and observationally, and have important implications for feedback in galactic systems. | the structure of multiphase galactic winds |
searches for electromagnetic counterparts of gravitational-wave signals have redoubled since the first detection in 2017 of a binary neutron star merger with a gamma-ray burst, optical/infrared kilonova, and panchromatic afterglow. yet, one ligo/virgo observing run later, there has not yet been a second, secure identification of an electromagnetic counterpart. this is not surprising given that the localization uncertainties of events in ligo and virgo's third observing run, o3, were much larger than predicted. we explain this by showing that improvements in data analysis that now allow ligo/virgo to detect weaker and hence more poorly localized events have increased the overall number of detections, of which well-localized, gold-plated events make up a smaller proportion overall. we present simulations of the next two ligo/virgo/kagra observing runs, o4 and o5, that are grounded in the statistics of o3 public alerts. to illustrate the significant impact that the updated predictions can have, we study the follow-up strategy for the zwicky transient facility. realistic and timely forecasting of gravitational-wave localization accuracy is paramount given the large commitments of telescope time and the need to prioritize which events are followed up. we include a data release of our simulated localizations as a public proposal planning resource for astronomers. | data-driven expectations for electromagnetic counterpart searches based on ligo/virgo public alerts |
investigating protostellar accretion (ipa) is a cycle 1 jwst program using the nirspec+miri ifus to obtain 2.9--28 $\mu$m spectral cubes of five young protostars with luminosities of 0.2 to 10,000 l$_{\odot}$ in their primary accretion phase. this paper introduces the nirspec 2.9--5.3 $\mu$m data of the inner 840-9000 au with spatial resolutions from 28-300 au. the spectra show rising continuum emission, deep ice absorption, emission from h$_{2}$, h~i, and [fe~ii], and the co fundamental series in emission and absorption. maps of the continuum emission show scattered light cavities for all five protostars. in the cavities, collimated jets are detected in [fe~ii] for the four $< 320$~l$_{\odot}$ protostars, two of which are additionally traced in br-$\alpha$. knots of [fe~ii] emission are detected toward the most luminous protostar, and knots of [feii] emission with dynamical times of $< 30$~yrs are found in the jets of the others. while only one jet is traced in h$_2$, knots of h$_2$ and co are detected in the jets of four protostars. h$_2$ is seen extending through the cavities showing they are filled by warm molecular gas. bright h$_2$ emission is seen along the walls of a single cavity, while in three cavities, narrow shells of h$_2$ emission are found, one of which has an [fe~ii] knot at its apex. these data show cavities containing collimated jets traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle wind and/or gas accelerated by bow shocks in the jets. | investigating protostellar accretion-driven outflows across the mass spectrum: jwst nirspec ifu 3-5~$\\mu$m spectral mapping of five young protostars |
we report on the coordinated observations of the neutron star low-mass x-ray binary (ns-lmxb) \gx in x-rays (ixpe, nicer, nustar and integral), optical (rem and lco), near-infrared (rem), mid-infrared (vlt visir), and radio (atca). this z-source was observed by \ixpe twice in march-april 2023 (obs. 1 and 2). in the radio band, the source was detected, but only upper-limits to the linear polarization were obtained at a $3\sigma$ level of $6.1\%$ at 5.5 ghz and $5.9\%$ at 9 ghz in obs.~1 and $12.5\%$ at 5.5~ghz and $20\%$ at 9~ghz in obs.~2. the mid-ir, near-ir and optical observations suggest the presence of a compact jet which peaks in the mid- or far-ir. the x-ray polarization degree was found to be $3.7\% \pm 0.4 \%$ (at $90\%$ confidence level) during obs.~1 when the source was in the horizontal branch of the z-track and $1.8\% \pm 0.4 \%$ during obs.~2 when the source was in the normal-flaring branch. these results confirm the variation of polarization degree as a function of the position of the source in the color-color diagram as for previously observed z-track sources (cyg~x-2 and xte~1701$-$462). evidence for a variation of the polarization angle $\sim 20^\circ$ with energy is found in both observations, likely related to the different, non-orthogonal polarization angles of the disk and comptonization components which peak at different energies. | discovery of a variable energy-dependent x-ray polarization in the accreting neutron star gx 5-1 |
the detection of numerous and relatively bright galaxies at redshifts z > 9 has prompted new investigations into the star-forming properties of high-redshift galaxies. using local forms of the initial mass function (imf) to estimate stellar masses of these galaxies from their light output leads to galaxy masses that are at the limit allowed for the state of the lambdacdm universe at their redshift. we explore how varying the imf assumed in studies of galaxies in the early universe changes the inferred values for the stellar masses of these galaxies. we infer galaxy properties with the sed fitting code prospector using varying imf parameterizations for a sample of 102 galaxies from the jwst advanced deep extragalactic survey (jades) spectroscopically confirmed to be at z > 6.7, with additional photometry from the jwst extragalactic medium band survey (jems) for twenty-one galaxies. we demonstrate that models with stellar masses reduced by a factor of three or more do not affect the modeled spectral energy distribution (sed). | jades: using nircam photometry to investigate the dependence of stellar mass inferences on the imf in the early universe |
stars move away from their birth places over time via a process known as radial migration, which blurs chemo-kinematic relations used for reconstructing the milky way formation history. one of the ultimate goals of galactic archaeology, therefore, is to find stars' birth aggregates in the disk via chemical tagging. here we show that stellar birth radii can be derived directly from the data with minimum prior assumptions on the galactic enrichment history. we recover the time evolution of the stellar birth metallicity gradient, $d$[fe/h]($r$, $\tau$)/$dr$, through its inverse relation to the metallicity range as a function of age today, allowing us to place any star with age and metallicity measurements back to its birthplace, $r_b$. applying our method to a high-precision large data set of milky way disk subgiant stars, we find a steepening of the birth metallicity gradient from 11 to 8 gyr ago, which coincides with the time of the last major merger, gaia-sausage-enceladus (gse). this transition appears to play a major role in shaping both the age-metallicity relation and the bimodality in the [$\alpha$/fe]-[fe/h] plane. by dissecting the disk into mono-$r_b$ populations, clumps in the low-[$\alpha$/fe] sequence appear, which are not seen in the total sample and coincide in time with known star-formation bursts. we estimated that the sun was born at $4.5 \pm 0.4$ kpc from the galactic center. our $r_b$ estimates provide the missing piece needed to recover the milky way formation history, while the by-product,[fe/h]$(r$, $\tau)$, can be used as the thus-far missing prior for chemical evolution modeling. | there is no place like home -- finding birth radii of stars in the milky way |
current theoretical models predict a mass gap with a dearth of stellar black holes (bhs) between roughly 50 m ⊙ and 100 m ⊙, while above the range accessible through massive star evolution, intermediate-mass bhs (imbhs) still remain elusive. repeated mergers of binary bhs, detectable via gravitational-wave emission with the current ligo/virgo/kagra interferometers and future detectors such as lisa or the einstein telescope, can form both mass-gap bhs and imbhs. here we explore the possibility that mass-gap bhs and imbhs are born as a result of successive bh mergers in dense star clusters. in particular, nuclear star clusters at the centers of galaxies have deep enough potential wells to retain most of the bh merger products after they receive significant recoil kicks due to anisotropic emission of gravitational radiation. using for the first time simulations that include full stellar evolution, we show that a massive stellar bh seed can easily grow to ~103-104 m ⊙ as a result of repeated mergers with other smaller bhs. we find that lowering the cluster metallicity leads to larger final bh masses. we also show that the growing bh spin tends to decrease in magnitude with the number of mergers so that a negative correlation exists between the final mass and spin of the resulting imbhs. assumptions about the birth spins of stellar bhs affect our results significantly, with low birth spins leading to the production of a larger population of massive bhs. | repeated mergers, mass-gap black holes, and formation of intermediate-mass black holes in dense massive star clusters |
the era of the james webb space telescope ushers stellar population models into uncharted territories, particularly at the high-redshift frontier. in a companion paper, we apply the \texttt{prospector} bayesian framework to jointly infer galaxy redshifts and stellar population properties from broad-band photometry as part of the uncover survey. here we present a comprehensive error budget in spectral energy distribution (sed) modeling. using a sample selected to have photometric redshifts higher than 9, we quantify the systematic shifts stemming from various model choices in inferred stellar mass, star formation rate (sfr), and age. these choices encompass different timescales for changes in the star formation history (sfh), non-universal stellar initial mass functions (imf), and the inclusion of variable nebular abundances, gas density and ionizing photon budget. we find that the imf exerts the strongest influence on the inferred properties: the systematic uncertainties can be as much as 1 dex, 2--5 times larger than the formal reported uncertainties in mass and sfr; and importantly, exceed the scatter seen when using different sed fitting codes. although the assumptions on the lower end of the imf induce degeneracy, our findings suggest that a common practice in the literature of assessing uncertainties in sed-fitting processes by comparing multiple codes is substantively underestimating the true systematic uncertainty. highly stochastic sfhs change the inferred sfh by much larger than the formal uncertainties, and introduce $\sim 0.8$ dex systematics in sfr averaged over short time scale and $\sim 0.3$ dex systematics in average age. finally, employing a flexible nebular emission model causes $\sim 0.2$ dex systematic increase in mass and sfr, comparable to the formal uncertainty. this paper constitutes an initial step toward a complete uncertainty estimate in sed modeling. | quantifying the effects of known unknowns on inferred high-redshift galaxy properties: burstiness, the imf, and nebular physics |
cosmic hydrogen reionization and cosmic production of first metals are major phase transitions of the universe occurring during the first billion years after the big bang, but still poorly explored observationally. using the jwst nirspec prism spectroscopy, we report the discovery of a sub-$l_{\ast}$ galaxy at $z_{\rm spec}=8.1623_{-0.0008}^{+0.0007}$, dubbed rxj2129-z8heii, via the detection of a series of strong rest-frame uv/optical nebular emission lines and the clear lyman break. a strong he ii $\lambda$1640 emission is present, the highest redshift he ii line currently known. its high rest-frame equivalent width (ew $=19.4\pm3.2$ angstrom) and extreme flux ratios with respect to uv metal lines and balmer lines raise the possibility that part of rxj2129-z8heii's stellar populations could be pop iii-like. rxj2129-z8heii also shows a pronounced uv continuum with an extremely steep (i.e. blue) spectral slope of $\beta=-2.50\pm0.08$, the steepest amongst all spectroscopically confirmed galaxies at $z\gtrsim7$, in support of its very hard ionizing spectrum that could lead to a significant leakage of its ionizing flux. therefore, rxj2129-z8heii is representative of the key galaxy population driving the cosmic reionization. to date, this is also the most compelling case where trace pop iii stars might coexist with more metal-enriched stars. | a strong he ii $\\lambda$1640 emitter with extremely blue uv spectral slope at $z=8.16$: presence of pop iii stars? |
one promising electromagnetic signature of compact object mergers are kilonovae: approximately isotropic radioactively powered transients that peak days to weeks post-merger. key uncertainties in kilonova modeling include the emission profiles of the radioactive decay products—non-thermal β -particles, α -particles, fission fragments, and γ -rays—and the efficiency with which their kinetic energy is absorbed by the ejecta. the radioactive energy emitted, along with its thermalization efficiency, sets the luminosity budget and is therefore crucial for predicting kilonova light curves. we outline uncertainties in the radioactivity, describe the processes by which the decay products transfer energy to the ejecta, and calculate time-dependent thermalization efficiencies for each particle type. we determine the net thermalization efficiency and explore its dependence on r-process yields—in particular, the production of α -decaying translead nuclei—and on ejecta mass, velocity, and magnetic fields. we incorporate our results into detailed radiation transport simulations, and calculate updated kilonova light curve predictions. thermalization effects reduce kilonova luminosities by a factor of roughly 2 at peak, and by an order of magnitude at later times (15 days or more after explosion). we present analytic fits to time-dependent thermalization efficiencies, which can be used to improve light curve models. we revisit the putative kilonova that accompanied gamma-ray burst 130603b, and estimate the mass ejected in that event. we find later time kilonova light curves can be significantly impacted by α -decay from translead isotopes; data at these times may therefore be diagnostic of ejecta abundances. | radioactivity and thermalization in the ejecta of compact object mergers and their impact on kilonova light curves |
the early-science observations made by the james webb space telescope (jwst) have revealed an excess of ultra-massive galaxy candidates that appear to challenge the standard cosmological model ($\lambda$cdm). here, we argue that any modifications to $\lambda$cdm that can produce such ultra-massive galaxies in the early universe would also affect the uv galaxy luminosity function (uv lf) inferred from the hubble space telescope (hst). the uv lf covers the same redshifts ($z\approx 7-10$) and host-halo masses $(m_\mathrm{h}\approx 10^{10}-10^{12}\, m_\odot$) as the jwst candidates, but tracks star-formation rate rather than stellar mass. we consider beyond-$\lambda$cdm power-spectrum enhancements and show that any departure large enough to reproduce the abundance of ultra-massive jwst candidates is in conflict with the hst data. our analysis, therefore, severely disfavors a cosmological explanation for the jwst abundance problem. looking ahead, we determine the maximum allowable stellar-mass function and provide projections for the high-$z$ uv lf given our constraints on cosmology from current hst data. | insights from hst into ultra-massive galaxies and early-universe cosmology |
context. gaia dr3 contains 1.8 billion sources with g-band photometry, 1.5 billion of which with gbp and grp photometry, complemented by positions on the sky, parallax, and proper motion. the median number of field-of-view transits in the three photometric bands is between 40 and 44 measurements per source and covers 34 months of data collection.aims: we pursue a classification of galactic and extra-galactic objects that are detected as variable by gaia across the whole sky.methods: supervised machine learning (extreme gradient boosting and random forest) was employed to generate multi-class, binary, and meta-classifiers that classified variable objects with photometric time series in the g, gbp, and grp bands.results: classification results comprise 12.4 million sources (selected from a much larger set of potential variable objects) and include about 9 million variable stars classified into 22 variability types in the milky way and nearby galaxies such as the magellanic clouds and andromeda, plus thousands of supernova explosions in distant galaxies, 1 million active galactic nuclei, and almost 2.5 million galaxies. the identification of galaxies was made possible by the artificial variability of extended objects as detected by gaia, so they were published in the galaxy_candidates table of the gaia dr3 archive, separate from the classifications of genuine variability (in the vari_classifier_result table). the latter contains 24 variability classes or class groups of periodic and non-periodic variables (pulsating, eclipsing, rotating, eruptive, cataclysmic, stochastic, and microlensing), with amplitudes from a few milli-magnitudes to several magnitudes. | gaia data release 3. all-sky classification of 12.4 million variable sources into 25 classes |
for the past 400 years, astronomers have sought to observe and interpret the universe by building more powerful telescopes. these incredible instruments extend the capabilities of one of our most important senses, sight, towards new limits such as increased sensitivity and resolution, new dimensions such as exploration of wavelengths across the full electromagnetic spectrum, new information content such as analysis through spectroscopy, and new cadences such as rapid time-series views of the variable sky. the results from these investments, from small to large telescopes on the ground and in space, have completely transformed our understanding of the universe; including the discovery that earth is not the center of the universe, that the milky way is one among many galaxies in the universe, that relic cosmic background radiation fills all space in the early universe, that that the expansion rate of the universe is accelerating, that exoplanets are common around stars, that gravitational waves exist, and much more. for modern astronomical research, the next wave of breakthroughs in fields ranging over planetary, stellar, galactic, and extragalactic science motivate a general-purpose observatory that is optimized at near- and mid-infrared wavelengths, and that has much greater sensitivity, resolution, and spectroscopic multiplexing than all previous telescopes. this scientific vision, from measuring the composition of rocky worlds in the nearby milky way galaxy to finding the first sources of light in the universe to other topics at the forefront of modern astrophysics, motivates the state-of-the-art james webb space telescope (webb). in this review paper, i summarize the design and technical capabilities of webb and the scientific opportunities that it enables. | scientific discovery with the james webb space telescope |
the cosmological relaxion can address the hierarchy problem, while its coherent oscillations can constitute dark matter in the present universe. we consider the possibility that the relaxion forms gravitationally bound objects that we denote as relaxion stars. the density of these stars would be higher than that of the local dark matter density, resulting in enhanced signals in table-top detectors, among others. furthermore, we raise the possibility that these objects may be trapped by an external gravitational potential, such as that of the earth or the sun. this leads to formation of relaxion halos of even greater density. we discuss several interesting implications of relaxion halos, as well as detection strategies to probe them. here, we show that current and near-future atomic physics experiments can probe physical models of relaxion dark matter in scenarios of bound relaxion halos around the earth or sun. | relaxion stars and their detection via atomic physics |
the thermodynamic properties of high temperature and high density qcd matter are explored within the chiral su(3)-flavor parity-doublet polyakov-loop quark-hadron mean-field model, cmf. the quark sector of the cmf model is tuned to describe the μb=0 thermodynamics data of lattice qcd. the resulting lines of constant physical variables as well as the baryon number susceptibilities are studied in some detail in the temperature-chemical-potential plane. the cmf model predicts three consecutive transitions: the nuclear first-order liquid-vapor phase transition, chiral symmetry restoration, and the crossover transition to a quark matter phase. all three phenomena are crossovers, for most of the t -μb plane. the deviations from the free ideal hadron gas baseline at μb=0 and t ≈100 -200 mev can be attributed to remnants of the liquid-vapor first-order phase transition in nuclear matter. the chiral crossing transition determines the baryon fluctuations at much higher μb≈1.5 gev. at high baryon densities, μb≈2.4 gev, the behavior of fluctuations is controlled by crossover to quark matter. the cmf model also describe well the static properties of high μb neutron stars as well as recent neutron star merger observations. the effective equation of state presented here describes simultaneously lattice qcd results at μb=0 as well as observed physical phenomena (nuclear matter and neutron star matter) at t ≅0 and high densities, μb>1 gev. | equation of state for hot qcd and compact stars from a mean-field approach |
we present results from the "mint" resolution dc justice league suite of milky way-like zoom-in cosmological simulations, which extend our study of nearby galaxies down into the ultrafaint dwarf (ufd) regime for the first time. the mass resolution of these simulations is the highest ever published for cosmological milky way zoom-in simulations run to z = 0, with initial star (dark matter) particle masses of 994 (17900) m⊙, and a force resolution of 87 pc. we study the surrounding dwarfs and ufds, and find that the simulations match the observed dynamical properties of galaxies with -3 > mv > -19, and reproduce the scatter seen in the size-luminosity plane for rh ≳ 200 pc. we predict the vast majority of nearby galaxies will be observable by the vera rubin observatory's coadded legacy survey of space and time. we additionally show that faint dwarfs with velocity dispersions ≲5 km s-1 result from severe tidal stripping of the host halo. we investigate the quenching of ufds in a hydrodynamical milky way context and find that the majority of ufds are quenched prior to interactions with the milky way, though some of the quenched ufds retain their gas until infall. additionally, these simulations yield some unique dwarfs that are the first of their kind to be simulated, e.g., an h i-rich field ufd, a late-forming ufd that has structural properties similar to crater 2, as well as a compact dwarf satellite that has no dark matter at z = 0. | ultrafaint dwarfs in a milky way context: introducing the mint condition dc justice league simulations |
we measure planet occurrence rates using the planet candidates discovered by the q1-q16 kepler pipeline search. this study examines planet occurrence rates for the kepler gk dwarf target sample for planet radii, 0.75 ≤slant {r}{{p}} ≤slant 2.5 {r}\oplus , and orbital periods, 50 ≤slant {p}{orb} ≤slant 300 days, with an emphasis on a thorough exploration and identification of the most important sources of systematic uncertainties. integrating over this parameter space, we measure an occurrence rate of f0 = 0.77 planets per star, with an allowed range of 0.3≤slant {f}0 ≤slant 1.9. the allowed range takes into account both statistical and systematic uncertainties, and values of f0 beyond the allowed range are significantly in disagreement with our analysis. we generally find higher planet occurrence rates and a steeper increase in planet occurrence rates toward small planets than previous studies of the kepler gk dwarf sample. through extrapolation, we find that the one year orbital period terrestrial planet occurrence rate {\zeta }1.0 = 0.1, with an allowed range of 0.01≤slant {\zeta }1.0 ≤slant 2, where {\zeta }1.0 is defined as the number of planets per star within 20% of the {r}{{p}} and {p}{orb} of earth. for g dwarf hosts, the {\zeta }1.0 parameter space is a subset of the larger {η }\oplusparameter space, thus {\zeta }1.0 places a lower limit on {η }\oplusfor g dwarf hosts. from our analysis, we identify the leading sources of systematics impacting kepler occurrence rate determinations as reliability of the planet candidate sample, planet radii, pipeline completeness, and stellar parameters. | terrestrial planet occurrence rates for the kepler gk dwarf sample |
context. the formation stage of planetesimals represents a major gap in our understanding of the planet formation process. late-stage planet accretion models typically make arbitrary assumptions about planetesimal and pebble distribution, while dust evolution models predict that planetesimal formation is only possible at some orbital distances.aims: we wish to test the importance of the water snow line in triggering the formation of the first planetesimals during the gas-rich phase of a protoplanetary disk, when cores of giant planets have to form.methods: we connected prescriptions for gas disk evolution, dust growth and fragmentation, water ice evaporation and recondensation, the transport of both solids and water vapor, and planetesimal formation via streaming instability into a single one-dimensional model for protoplanetary disk evolution.results: we find that processes taking place around the snow line facilitate planetesimal formation in two ways. first, because the sticking properties between wet and dry aggregates change, a "traffic jam" inside of the snow line slows the fall of solids onto the star. second, ice evaporation and outward diffusion of water followed by its recondensation increases the abundance of icy pebbles that trigger planetesimal formation via streaming instability just outside of the snow line.conclusions: planetesimal formation is hindered by growth barriers and radial drift and thus requires particular conditions to take place. the snow line is a favorable location where planetesimal formation is possible for a wide range of conditions, but not in every protoplanetary disk model, however. this process is particularly promoted in large cool disks with low intrinsic turbulence and an increased initial dust-to-gas ratio. the movie attached to fig. 3 is only available at http://www.aanda.org | planetesimal formation starts at the snow line |
context. kelt-9 b exemplifies a newly emerging class of short-period gaseous exoplanets that tend to orbit hot, early type stars - termed ultra-hot jupiters. the severe stellar irradiation heats their atmospheres to temperatures of 4000 k, similar to temperatures of photospheres of dwarf stars. due to the absence of aerosols and complex molecular chemistry at such temperatures, these planets offer the potential of detailed chemical characterization through transit and day-side spectroscopy. detailed studies of their chemical inventories may provide crucial constraints on their formation process(es) and evolution history.aims: we aim to search the optical transmission spectrum of kelt-9 b for absorption lines by metals using the cross-correlation technique.methods: we analysed two transit observations obtained with the harps-n spectrograph. we used an isothermal equilibrium chemistry model to predict the transmission spectrum for each of the neutral and singly ionized atoms with atomic numbers between three and 78. of these, we identified the elements that are expected to have spectral lines in the visible wavelength range and used those as cross-correlation templates.results: we detect (>5σ) absorption by na i, cr ii, sc ii and y ii, and confirm previous detections of mg i, fe i, fe ii, and ti ii. in addition, we find evidence of ca i, cr i, co i, and sr ii that will require further observations to verify. the detected absorption lines are significantly deeper than predicted by our model, suggesting that the material is transported to higher altitudes where the density is enhanced compared to a hydrostatic profile, and that the material is part of an extended or outflowing envelope. there appears to be no significant blue-shift of the absorption spectrum due to a net day-to-night side wind. in particular, the strong fe ii feature is shifted by 0.18 ± 0.27 km s-1, consistent with zero. using the orbital velocity of the planet we derive revised masses and radii of the star and the planet: m* = 1.978 ± 0.023 m⊙, r* = 2.178 ± 0.011 r⊙, mp = 2.44 ± 0.70 mj and rp = 1.783 ± 0.009 rj. cross-correlation templates are available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/627/a165 | a spectral survey of an ultra-hot jupiter. detection of metals in the transmission spectrum of kelt-9 b |
strange stars (sss) are compact objects made of deconfined quarks. it is hard to distinguish sss from neutron stars as a thin crust composed of normal hadronic matter may exist and obscure the whole surface of the ss. here we suggest that the intriguing repeating fast radio bursts (frbs) are produced by the intermittent fractional collapses of the crust of an ss induced by refilling of materials accreted from its low-mass companion. the periodic/sporadic/clustered temporal behaviors of frbs could be well understood in our scenario. especially, the periodicity is attributed to the modulation of accretion rate through the disk instabilities. to account for a ~16-day periodicity of the repeating frb source of 180916.j0158+65, a shakura-sunyaev disk with a viscosity parameter of 0.004 and an accretion rate of 3 × 1016 g s-1 is invoked. our scenario, if favored by future observations, will serve as indirect evidence for the strange quark matter hypothesis. | repeating fast radio bursts from collapses of the crust of a strange star |
we demonstrate that ab-initio calculations in qcd at high densities offer significant and nontrivial information about the equation of state of matter in the cores of neutron stars, going beyond that which is obtainable from current astrophysical observations. we do so by extrapolating the equation of state to neutron-star densities using a gaussian process and conditioning it sequentially with astrophysical observations and qcd input. using our recent work, imposing the latter does not require an extrapolation to asymptotically high density. we find the qcd input to be complementary to the astrophysical observations, offering strong additional constraints at the highest densities reached in the cores of neutron stars; with the qcd input, the equation of state is no longer prior dominated at any density. the qcd input reduces the pressure and speed of sound at high densities, and it predicts that binary collisions of equal-mass neutron stars will produce a black hole with greater than 95% (68%) credence for masses m ≥ 1.38m ⊙ (m ≥ 1.25m ⊙). we provide a python implementation of the qcd likelihood function so that it can be conveniently used within other inference setups. | ab-initio qcd calculations impact the inference of the neutron-star-matter equation of state |
we present and characterize the catalog of galaxy shape measurements that will be used for cosmological weak lensing measurements in the wide layer of the first year of the hyper suprime-cam (hsc) survey. the catalog covers an area of 136.9 deg2 split into six fields, with a mean i-band seeing of 0{^''.}58 and 5σ point-source depth of i ∼ 26. given conservative galaxy selection criteria for first-year science, the depth and excellent image quality results in unweighted and weighted source number densities of 24.6 and 21.8 arcmin-2, respectively. we define the requirements for cosmological weak lensing science with this catalog, then focus on characterizing potential systematics in the catalog using a series of internal null tests for problems with point-spread function (psf) modeling, shear estimation, and other aspects of the image processing. we find that the psf models narrowly meet requirements for weak lensing science with this catalog, with fractional psf model size residuals of approximately 0.003 (requirement: 0.004) and the psf model shape correlation function ρ1 < 3 × 10-7 (requirement: 4 × 10-7) at 0.5° scales. a variety of galaxy shape-related null tests are statistically consistent with zero, but star-galaxy shape correlations reveal additive systematics on >1° scales that are sufficiently large as to require mitigation in cosmic shear measurements. finally, we discuss the dominant systematics and the planned algorithmic changes to reduce them in future data reductions. | the first-year shear catalog of the subaru hyper suprime-cam subaru strategic program survey |
the details of the physical mechanism that drives core-collapse supernovae (ccsne) remain uncertain. while there is an emerging consensus on the qualitative outcome of detailed ccsn mechanism simulations in 2d, only recently have high-fidelity 3d simulations become possible. here we present the results of an extensive set of 3d ccsn simulations using high-fidelity multidimensional neutrino transport, high-resolution hydrodynamics, and approximate general relativistic gravity. we employ a state-of-the-art 20 m ⊙ progenitor generated using modules for experiments in stellar astrophysics, and the sfho equation of state. while none of our 3d ccsn simulations explode within ∼500 ms after core bounce, we find that the presence of large-scale aspherical motion in the si and o shells aid shock expansion and bring the models closer to the threshold of explosion. we also find some dependence on resolution and geometry (octant versus full 4π). as has been noted in other recent works, we find that the post-shock turbulence plays an important role in determining the overall dynamical evolution of our simulations. we find a strong standing accretion shock instability (sasi) that develops at late times. the sasi produces transient shock expansions, but these do not result in any explosions. we also report that for a subset of our simulations, we find conclusive evidence for the lepton-number emission self-sustained asymmetry, which until now has not been confirmed by independent simulation codes. both the progenitor asphericities and the sasi-induced transient shock expansion phases generate transient gravitational waves and neutrino signal modulations via perturbations of the protoneutron star by turbulent motions. | exploring fundamentally three-dimensional phenomena in high-fidelity simulations of core-collapse supernovae |
protoplanetary disks are known to possess a variety of substructures in the distribution of their millimetre-sized grains, predominantly seen as rings and gaps1, which are frequently interpreted as arising from the shepherding of large grains by either hidden, still-forming planets within the disk2 or (magneto-)hydrodynamic instabilities3. the velocity structure of the gas offers a unique probe of both the underlying mechanisms driving the evolution of the disk—such as movement of planet-building material from volatile-rich regions to the chemically inert midplane—and the details of the required removal of angular momentum. here we report radial profiles of the three velocity components of gas in the upper layers of the disk of the young star hd 163296, as traced by emission from 12co molecules. these velocities reveal substantial flows from the surface of the disk towards its midplane at the radial locations of gaps that have been argued to be opened by embedded planets4-7: these flows bear a striking resemblance to meridional flows, long predicted to occur during the early stages of planet formation8-12. in addition, a persistent radial outflow is seen at the outer edge of the disk that is potentially the base of a wind associated with previously detected extended emission12. | meridional flows in the disk around a young star |
apogee-2 is a high-resolution, near-infrared spectroscopic survey observing ∼3 × 105 stars across the entire sky. it is the successor to apogee and is part of the sloan digital sky survey iv (sdss-iv). apogee-2 is expanding on apogee's goals of addressing critical questions of stellar astrophysics, stellar populations, and galactic chemodynamical evolution using (1) an enhanced set of target types and (2) a second spectrograph at las campanas observatory in chile. apogee-2 is targeting red giant branch and red clump stars, rr lyrae, low-mass dwarf stars, young stellar objects, and numerous other milky way and local group sources across the entire sky from both hemispheres. in this paper, we describe the apogee-2 observational design, target selection catalogs and algorithms, and the targeting-related documentation included in the sdss data releases. | target selection for the sdss-iv apogee-2 survey |
we describe system verification tests and early science results from the pulsar processor (ptuse) developed for the newly commissioned 64-dish sarao meerkat radio telescope in south africa. meerkat is a high-gain ( ${∼}2.8 \mbox{k jy}^{-1}$ ) low-system temperature ( ${∼}18 \mbox{k at }20 \mbox{cm}$ ) radio array that currently operates at 580-1 670 mhz and can produce tied-array beams suitable for pulsar observations. this paper presents results from the meertime large survey project and commissioning tests with ptuse. highlights include observations of the double pulsar $\mbox{j}0737{-}3039\mbox{a}$ , pulse profiles from 34 millisecond pulsars (msps) from a single 2.5-h observation of the globular cluster terzan 5, the rotation measure of ter5o, a 420-sigma giant pulse from the large magellanic cloud pulsar psr $\mbox{j}0540{-}6919$ , and nulling identified in the slow pulsar psr j0633-2015. one of the key design specifications for meerkat was absolute timing errors of less than 5 ns using their novel precise time system. our timing of two bright msps confirm that meerkat delivers exceptional timing. psr $\mbox{j}2241{-}5236$ exhibits a jitter limit of $<4 \mbox{ns h}^{-1}$ whilst timing of psr $\mbox{j}1909{-}3744$ over almost 11 months yields an rms residual of 66 ns with only 4 min integrations. our results confirm that the meerkat is an exceptional pulsar telescope. the array can be split into four separate sub-arrays to time over 1 000 pulsars per day and the future deployment of s-band (1 750-3 500 mhz) receivers will further enhance its capabilities. | the meerkat telescope as a pulsar facility: system verification and early science results from meertime |
the majority of massive stars live in binary or multiple systems and will interact with a companion during their lifetimes, which helps to explain the observed diversity of core-collapse supernovae. donor stars in binary systems can lose most of their hydrogen-rich envelopes through mass transfer. as a result, not only are the surface properties affected, but so is the core structure. however, most calculations of the core-collapse properties of massive stars rely on single-star models. we present a systematic study of the difference between the pre-supernova structures of single stars and stars of the same initial mass (11-21 m⊙) that have been stripped due to stable post-main-sequence mass transfer at solar metallicity. we present the pre-supernova core composition with novel diagrams that give an intuitive representation of the isotope distribution. as shown in previous studies, at the edge of the carbon-oxygen core, the binary-stripped star models contain an extended gradient of carbon, oxygen, and neon. this layer remains until core collapse and is more extended in mass for higher initial stellar masses. it originates from the receding of the convective helium core during core helium burning in binary-stripped stars, which does not occur in single-star models. we find that this same evolutionary phase leads to systematic differences in the final density and nuclear energy generation profiles. binary-stripped star models have systematically higher total masses of carbon at the moment of core collapse compared to single-star models, which likely results in systematically different supernova yields. in about half of our models, the silicon-burning and oxygen-rich layers merge after core silicon burning. we discuss the implications of our findings for the "explodability", supernova observations, and nucleosynthesis of these stars. our models are publicly available and can be readily used as input for detailed supernova simulations. | different to the core: the pre-supernova structures of massive single and binary-stripped stars |
the atmospheres of gaseous giant exoplanets orbiting close to their parent stars (hot jupiters) have been probed for nearly two decades1,2. they allow us to investigate the chemical and physical properties of planetary atmospheres under extreme irradiation conditions3. previous observations of hot jupiters as they transit in front of their host stars have revealed the frequent presence of water vapour4 and carbon monoxide5 in their atmospheres; this has been studied in terms of scaled solar composition6 under the usual assumption of chemical equilibrium. both molecules as well as hydrogen cyanide were found in the atmosphere of hd 209458b5,7,8, a well studied hot jupiter (with equilibrium temperature around 1,500 kelvin), whereas ammonia was tentatively detected there9 and subsequently refuted10. here we report observations of hd 209458b that indicate the presence of water (h2o), carbon monoxide (co), hydrogen cyanide (hcn), methane (ch4), ammonia (nh3) and acetylene (c2h2), with statistical significance of 5.3 to 9.9 standard deviations per molecule. atmospheric models in radiative and chemical equilibrium that account for the detected species indicate a carbon-rich chemistry with a carbon-to-oxygen ratio close to or greater than 1, higher than the solar value (0.55). according to existing models relating the atmospheric chemistry to planet formation and migration scenarios3,11,12, this would suggest that hd 209458b formed far from its present location and subsequently migrated inwards11,13. other hot jupiters may also show a richer chemistry than has been previously found, which would bring into question the frequently made assumption that they have solar-like and oxygen-rich compositions. | five carbon- and nitrogen-bearing species in a hot giant planet's atmosphere |
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