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context: the extreme luminosity of gamma-ray bursts (grbs) makes them powerful beacons for studies of the distant universe. the most luminous bursts are typically detected at moderate/high redshift, where the volume for seeing such rare events is maximized and the star-formation activity is greater than at z = 0. for distant events, not all observations are feasible, such as at tev energies. aims: here we present a spectroscopic redshift measurement for the exceptional grb 221009a, the brightest grb observed to date with emission extending well into the tev regime. methods: we used the x-shooter spectrograph at the eso very large telescope (vlt) to obtain simultaneous optical to near-ir spectroscopy of the burst afterglow 0.5 days after the explosion. results: the spectra exhibit both absorption and emission lines from material in a host galaxy at z = 0.151. thus grb 221009a was a relatively nearby burst with a luminosity distance of 745 mpc. its host galaxy properties (star-formation rate and metallicity) are consistent with those of lgrb hosts at low redshift. this redshift measurement yields information on the energy of the burst. the inferred isotropic energy release, $e_{\rm iso} > 5 \times 10^{54}$ erg, lies at the high end of the distribution, making grb 221009a one of the nearest and also most energetic grbs observed to date. we estimate that such a combination (nearby as well as intrinsically bright) occurs between once every few decades to once per millennium. | the brightest grb ever detected: grb 221009a as a highly luminous event at z = 0.151 |
fast radio bursts (frbs) are millisecond radio pulses originating from powerful enigmatic sources at extragalactic distances. neutron stars with large magnetic fields (magnetars) have been considered as the sources powering the frbs, but the connection requires further substantiation. here we report the detection by the agile satellite on 28 april 2020 of an x-ray burst in temporal coincidence with a bright frb-like radio burst from the galactic magnetar sgr 1935+2154. the burst observed in the hard x-ray band (18-60 kev) lasted about 0.5 s, it is spectrally cut off above 80 kev and implies an isotropically emitted energy of about 1040 erg. this event demonstrates that a magnetar can produce x-ray bursts in coincidence with frb-like radio bursts. it also suggests that frbs associated with magnetars can emit x-ray bursts. we discuss sgr 1935+2154 in the context of frbs with low-intermediate radio energies in the range 1038-1040 erg. magnetars with magnetic fields b ≈ 1015 g may power these frbs, and new data on the search for x-ray emission from frbs are presented. we constrain the bursting x-ray energy of the nearby frb 180916 to be less than 1046 erg, smaller than that observed in giant flares from galactic magnetars. | an x-ray burst from a magnetar enlightening the mechanism of fast radio bursts |
the understanding of stellar structure represents the crossroads of our theories of the nuclear force and the gravitational interaction under the most extreme conditions observably accessible. it provides a powerful probe of the strong field regime of general relativity, and opens fruitful avenues for the exploration of new gravitational physics. the latter can be captured via modified theories of gravity, which modify the einstein-hilbert action of general relativity and/or some of its principles. these theories typically change the tolman-oppenheimer-volkoff equations of stellar's hydrostatic equilibrium, thus having a large impact on the astrophysical properties of the corresponding stars and opening a new window to constrain these theories with present and future observations of different types of stars. for relativistic stars, such as neutron stars, the uncertainty on the equation of state of matter at supranuclear densities intertwines with the new parameters coming from the modified gravity side, providing a whole new phenomenology for the typical predictions of stellar structure models, such as mass-radius relations, maximum masses, or moment of inertia. for non-relativistic stars, such as white, brown and red dwarfs, the weakening/strengthening of the gravitational force inside astrophysical bodies via the modified newtonian (poisson) equation may induce changes on the star's mass, radius, central density or luminosity, having an impact, for instance, in the chandrasekhar's limit for white dwarfs, or in the minimum mass for stable hydrogen burning in high-mass brown dwarfs. this work aims to provide a broad overview of the main such results achieved in the recent literature for many such modified theories of gravity, by combining the results and constraints obtained from the analysis of relativistic and non-relativistic stars in different scenarios. moreover, we will build a bridge between the efforts of the community working on different theories, formulations, types of stars, theoretical modelings, and observational aspects, highlighting some of the most promising opportunities in the field. | stellar structure models in modified theories of gravity: lessons and challenges |
gravitational waves from binary coalescences provide one of the cleanest signatures of the nature of compact objects. it has been recently argued that the postmerger ringdown waveform of exotic ultracompact objects is initially identical to that of a black hole, and that putative corrections at the horizon scale will appear as secondary pulses after the main burst of radiation. here we extend this analysis in three important directions: (i) we show that this result applies to a large class of exotic compact objects with a photon sphere for generic orbits in the test-particle limit; (ii) we investigate the late-time ringdown in more detail, showing that it is universally characterized by a modulated and distorted train of "echoes"of the modes of vibration associated with the photon sphere; (iii) we study for the first time equal-mass, head-on collisions of two ultracompact boson stars and compare their gravitational-wave signal to that produced by a pair of black holes. if the initial objects are compact enough as to mimic a binary black-hole collision up to the merger, the final object exceeds the maximum mass for boson stars and collapses to a black hole. this suggests that—in some configurations—the coalescence of compact boson stars might be almost indistinguishable from that of black holes. on the other hand, generic configurations display peculiar signatures that can be searched for in gravitational-wave data as smoking guns of exotic compact objects. | gravitational-wave signatures of exotic compact objects and of quantum corrections at the horizon scale |
we perform a study of stellar flares for the 24,809 stars observed with 2 minute cadence during the first two months of the tess mission. flares may erode exoplanets' atmospheres and impact their habitability, but might also trigger the genesis of life around small stars. tess provides a new sample of bright dwarf stars in our galactic neighborhood, collecting data for thousands of m dwarfs that might host habitable exoplanets. here, we use an automated search for flares accompanied by visual inspection. then, our public allesfitter code robustly selects the appropriate model for potentially complex flares via bayesian evidence. we identify 1228 flaring stars, 673 of which are m dwarfs. among 8695 flares in total, the largest superflare increased the stellar brightness by a factor of 16.1. bolometric flare energies range from 1031.0 to 1036.9 erg, with a median of 1033.1 erg. furthermore, we study the flare rate and energy as a function of stellar type and rotation period. we solidify past findings that fast rotating m dwarfs are the most likely to flare and that their flare amplitude is independent of the rotation period. finally, we link our results to criteria for prebiotic chemistry, atmospheric loss through coronal mass ejections, and ozone sterilization. four of our flaring m dwarfs host exoplanet candidates alerted on by tess, for which we discuss how these effects can impact life. with upcoming tess data releases, our flare analysis can be expanded to almost all bright small stars, aiding in defining criteria for exoplanet habitability. | stellar flares from the first tess data release: exploring a new sample of m dwarfs |
we constrain the abundance of primordial black holes (pbh) using 2622 microlensing events obtained from 5-years observations of stars in the galactic bulge by the optical gravitational lensing experiment (ogle). the majority of microlensing events display a single or at least continuous population that has a peak around the light curve timescale te≃20 days and a wide distribution over the range te≃[1 ,300 ] days , while the data also indicates a second population of 6 ultrashort-timescale events in te≃[0.1 ,0.3 ] days , which are advocated to be due to free-floating planets. we confirm that the main population of ogle events can be well modeled by microlensing due to brown dwarfs, main sequence stars and stellar remnants (white dwarfs and neutron stars) in the standard galactic bulge and disk models for their spatial and velocity distributions. using the dark matter (dm) model for the milky way (mw) halo relative to the galactic bulge/disk models, we obtain the tightest upper bound on the pbh abundance in the mass range mpbh≃[10-6,10-3] m⊙ (earth-jupiter mass range), if we employ the "null hypothesis" that the ogle data does not contain any pbh microlensing event. more interestingly, we also show that earth-mass pbhs can well reproduce the 6 ultrashort-timescale events, without the need of free-floating planets, if the mass fraction of pbh to dm is at a per cent level, which is consistent with other constraints such as the microlensing search for andromeda galaxy (m31) and the longer timescale ogle events. our result gives a hint of pbh existence, and can be confirmed or falsified by microlensing search for stars in m31, because m31 is towards the mw halo direction and should therefore contain a much less number of free-floating planets, even if exist, than the direction to the mw center. | constraints on earth-mass primordial black holes from ogle 5-year microlensing events |
we present the first comprehensive study of r-process element nucleosynthesis in the ejecta of compact binary mergers (cbms) and their relic black hole (bh)-torus systems. the evolution of the bh-accretion tori is simulated for seconds with a newtonian hydrodynamics code including viscosity effects, pseudo-newtonian gravity for rotating bhs, and an energy-dependent two-moment closure scheme for the transport of electron neutrinos and antineutrinos. the investigated cases are guided by relativistic double neutron star (ns-ns) and ns-bh merger models, producing ∼3-6 m⊙ bhs with rotation parameters of abh ∼ 0.8 and tori of 0.03-0.3 m⊙. our nucleosynthesis analysis includes the dynamical (prompt) ejecta expelled during the cbm phase and the neutrino and viscously driven outflows of the relic bh-torus systems. while typically ∼20-25 per cent of the initial accretion-torus mass are lost by viscously driven outflows, neutrino-powered winds contribute at most another ∼1 per cent, but neutrino heating enhances the viscous ejecta significantly. since bh-torus ejecta possess a wide distribution of electron fractions (0.1-0.6) and entropies, they produce heavy elements from a ∼ 80 up to the actinides, with relative contributions of a ≳ 130 nuclei being subdominant and sensitively dependent on bh and torus masses and the exact treatment of shear viscosity. the combined ejecta of cbm and bh-torus phases can reproduce the solar abundances amazingly well for a ≳ 90. varying contributions of the torus ejecta might account for observed variations of lighter elements with 40 ≤ z ≤ 56 relative to heavier ones, and a considerable reduction of the prompt ejecta compared to the torus ejecta, e.g. in highly asymmetric ns-bh mergers, might explain the composition of heavy-element deficient stars. | comprehensive nucleosynthesis analysis for ejecta of compact binary mergers |
the mergers of double neutron star (ns-ns) and black hole (bh)-ns binaries are promising gravitational wave (gw) sources for advanced ligo and future gw detectors. the neutron-rich ejecta from such merger events undergoes rapid neutron capture (r-process) nucleosynthesis, enriching our galaxy with rare heavy elements like gold and platinum. the radioactive decay of these unstable nuclei also powers a rapidly evolving, supernova-like transient known as a "kilonova" (also known as "macronova"). kilonovae are an approximately isotropic electromagnetic counterpart to the gw signal, which also provides a unique and direct probe of an important, if not dominant, r-process site. i review the history and physics of kilonovae, leading to the current paradigm of week-long emission with a spectral peak at near-infrared wavelengths. using a simple light curve model to illustrate the basic physics, i introduce potentially important variations on this canonical picture, including: ∼day-long optical ("blue") emission from lanthanide-free components of the ejecta; ∼hour-long precursor uv/blue emission, powered by the decay of free neutrons in the outermost ejecta layers; and enhanced emission due to energy input from a long-lived central engine, such as an accreting bh or millisecond magnetar. i assess the prospects of kilonova detection following future gw detections of ns-ns/bh-ns mergers in light of the recent follow-up campaign of the ligo binary bh-bh mergers. | kilonovae |
at least 30% of main sequence stars host planets with sizes of between 1 and 4 earth radii and orbital periods of less than 100 days. we use n-body simulations including a model for gas-assisted pebble accretion and disk-planet tidal interaction to study the formation of super-earth systems. we show that the integrated pebble mass reservoir creates a bifurcation between hot super-earths or hot-neptunes (≲15 m⊕) and super-massive planetary cores potentially able to become gas giant planets (≳15 m⊕). simulations with moderate pebble fluxes grow multiple super-earth-mass planets that migrate inwards and pile up at the inner edge of the disk forming long resonant chains. we follow the long-term dynamical evolution of these systems and use the period ratio distribution of observed planet-pairs to constrain our model. up to ~95% of resonant chains become dynamically unstable after the gas disk dispersal, leading to a phase of late collisions that breaks the original resonant configurations. our simulations naturally match observations when they produce a dominant fraction (≳95%) of unstable systems with a sprinkling (≲5%) of stable resonant chains (the trappist-1 system represents one such example). our results demonstrate that super-earth systems are inherently multiple (n ≥ 2) and that the observed excess of single-planet transits is a consequence of the mutual inclinations excited by the planet-planet instability. in simulations in which planetary seeds are initially distributed in the inner and outer disk, close-in super-earths are systematically ice rich. this contrasts with the interpretation that most super-earths are rocky based on bulk-density measurements of super-earths and photo-evaporation modeling of their bimodal radius distribution. we investigate the conditions needed to form rocky super-earths. the formation of rocky super-earths requires special circumstances, such as far more efficient planetesimal formation well inside the snow line, or much faster planetary growth by pebble accretion in the inner disk. intriguingly, the necessary conditions to match the bulk of hot super-earths are at odds with the conditions needed to match the solar system. | formation of planetary systems by pebble accretion and migration. hot super-earth systems from breaking compact resonant chains |
the protagonists of the last great phase transition of the universe - cosmic reionization - remain elusive. faint star-forming galaxies are leading candidates because they are found to be numerous and may have significant ionizing photon escape fractions (fesc). here we update this picture via an empirical model that successfully predicts latest observations (e.g., the rapid drop in star-formation density (ρsfr at z > 8). we generate an ionizing spectrum for each galaxy in our model and constrain fesc by leveraging latest measurements of the reionization timeline (e.g., lyα damping of quasars and galaxies at z > 7). assuming a constant fesc across all sources at z > 6, we find muv < -13.5 galaxies need fesc = 0.21-0.04+0.06 to complete reionization. the inferred intergalactic medium neutral fraction is [0.9, 0.5, 0.1] at z=[8.2,6.8,6.2] ± 0.2 - that is, the bulk of reionization transpires rapidly in 300 myr, driven by the z > 8 ρsfr and favored by high neutral fractions (∼60%-90%) measured at z ∼ 7-8. inspired by the emergent sample of lyman continuum (lyc) leakers spanning z ∼ 0-6.6 that overwhelmingly displays higher-than-average star-formation surface density (σsfr), we propose a physically motivated model relating fesc to σsfr and find fesc ∝ σsfr0.4±0.1. since σsfr falls by ∼2.5 dex between z = 8 and z = 0, our model explains the humble upper limits on fesc at lower redshifts and its required evolution to fesc ∼ 0.2 at z > 6. within this model, strikingly, <5% of galaxies with muv < -18 and log(m⋆/m⊙) > 8 (the "oligarchs") account for ≳80% of the reionization budget - a stark departure from the canonical "democratic" reionization led by copious faint sources. in fact, faint sources (muv > -16) must be relegated to a limited role in order to ensure high neutral fractions at z = 7-8. shallow faint-end slopes of the uv luminosity function (αuv > -2) and/or fesc distributions skewed toward massive galaxies produce the required late and rapid reionization. we predict that lyc leakers like cola1 (z = 6.6, fesc ∼ 30%, muv = -21.5) will become increasingly common toward z ∼ 6 and that the drivers of reionization do not lie hidden across the faint end of the luminosity function but are already known to us. | rapid reionization by the oligarchs: the case for massive, uv-bright, star-forming galaxies with high escape fractions |
neutrino masses and mixings produce vacuum oscillations, an established quantum mechanical phenomenon. in matter, the mikheev-smirnov-wolfenstein effect, due to neutrino interactions with the background particles, triggers resonant flavor modification. in dense environments, such as core-collapse supernovae or compact mergers, sizable neutrino-neutrino interactions, shock waves and turbulence impact the neutrino flavor content under a variety of phenomena. theoretical approaches of neutrino propagation range from the mean-field approximation to the full quantum kinetic equations. intriguing connections have been uncovered between weakly interacting dense neutrino gases and other many-body systems and domains, from condensed matter and nuclear physics to quantum computing. besides the intrinsic theoretical interest, establishing how neutrinos change flavor contributes to answer the longstanding open questions of how massive stars explode and of the r-process sites. it is also important for future observations of core-collapse supernova neutrinos and of the diffuse supernova neutrino background that should be discovered in the foreseeable future. | neutrinos from dense environments : flavor mechanisms, theoretical approaches, observations, and new directions |
agama is a publicly available software library for a broad range of applications in the field of stellar dynamics. it provides methods for computing the gravitational potential of arbitrary analytic density profiles or n-body models, orbit integration and analysis, transformations between position/velocity and action/angle variables, distribution functions expressed in terms of actions and their moments, and iterative construction of self-consistent multicomponent galaxy models. applications include the inference about the structure of milky way or other galaxies from observations of stellar kinematics, preparation of equilibrium initial conditions for n-body simulations, and analysis of snapshots from simulations. the library is written in c++ , provides a python interface, and can be coupled to other stellar-dynamical software: amuse, galpy, and nemo. it is hosted at http://github.com/galacticdynamics-oxford/agama. | agama: action-based galaxy modelling architecture |
jwst is revolutionizing our understanding of the high-z universe by expanding the black hole horizon, looking farther and to smaller masses, and revealing the stellar light of their hosts. by examining jwst galaxies at z = 4-7 that host hα-detected black holes, we investigate (i) the high-z m •-m ⋆ relation and (ii) the black hole mass distribution, especially in its low-mass range (m • ≲ 106.5 m ⊙). with a detailed statistical analysis, our findings conclusively reveal a high-z m •-m ⋆ relation that deviates at >3σ confidence level from the local relation. the high-z relation is $\mathrm{log}({m}_{\bullet }/\,{m}_{\odot })=-{2.43}_{-0.83}^{+0.83}+{1.06}_{-0.09}^{+0.09}\mathrm{log}({m}_{\star }/\,{m}_{\odot })$ . black holes are overmassive by ~10-100× compared to their low-z counterparts in galactic hosts of the same stellar mass. this fact is not due to a selection effect in surveys. moreover, our analysis predicts the possibility of detecting in high-z jwst surveys 5-15× more black holes with m • ≲ 106.5 m ⊙, and 10-30× more with m • ≲ 108.5 m ⊙, compared to local relation's predictions. the lighter black holes preferentially occupy galaxies with a stellar mass of ~107.5-108 m ⊙. we have yet to detect these sources because (i) they may be inactive (duty cycles 1%-10%), (ii) the host overshines the active galactic nucleus (agn), or (iii) the agn is obscured and not immediately recognizable by line diagnostics. a search of low-mass black holes in existing jwst surveys will further test the m •-m ⋆ relation. current jwst fields represent a treasure trove of black hole systems at z = 4-7; their detection will provide crucial insights into their early evolution and coevolution with their galactic hosts. | jwst ceers and jades active galaxies at z = 4-7 violate the local m •-m ⋆ relation at >3σ: implications for low-mass black holes and seeding models |
we measure the circular velocity curve v c(r) of the milky way with the highest precision to date across galactocentric distances of 5 ≤ r ≤ 25 kpc. our analysis draws on the six-dimensional phase-space coordinates of ≳23,000 luminous red giant stars, for which we previously determined precise parallaxes using a data-driven model that combines spectral data from apogee with photometric information from wise, 2mass, and gaia. we derive the circular velocity curve with the jeans equation assuming an axisymmetric gravitational potential. at the location of the sun we determine the circular velocity with its formal uncertainty to be vc(r⊙ ) = (229.0+/- 0.2) km s-1 with systematic uncertainties at the ∼2%-5% level. we find that the velocity curve is gently but significantly declining at (-1.7 ± 0.1) km s-1 kpc-1, with a systematic uncertainty of 0.46 km s-1 kpc-1, beyond the inner 5 kpc. we exclude the inner 5 kpc from our analysis due to the presence of the galactic bar, which strongly influences the kinematic structure and requires modeling in a nonaxisymmetric potential. combining our results with external measurements of the mass distribution for the baryonic components of the milky way from other studies, we estimate the galaxy’s dark halo mass within the virial radius to be mvir = (7.25+/- 0.26)\cdot 1011 m⊙and a local dark matter density of ρ dm(r⊙ ) = 0.30+/- 0.03 gev cm-3. | the circular velocity curve of the milky way from 5 to 25 kpc |
the cold dark matter (cdm) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the milky way's dwarf galaxy satellites. we review the current observational and theoretical status of these "small-scale controversies." cosmological simulations that incorporate only gravity and collisionless cdm predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. the solution could lie in baryonic physics: recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the milky way do not host visible galaxies. however, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. for example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with cdm predictions. these observational approaches will get more powerful over the next few years. | cold dark matter: controversies on small scales |
ultracompact objects with light rings (lrs) but without an event horizon could mimic black holes (bhs) in their strong gravity phenomenology. but are such objects dynamically viable? stationary and axisymmetric ultracompact objects that can form from smooth, quasi-minkowski initial data must have at least one stable lr, which has been argued to trigger a spacetime instability; but its development and fate have been unknown. using fully nonlinear numerical evolutions of ultracompact bosonic stars free of any other known instabilities and introducing a novel adiabatic effective potential technique, we confirm the lrs triggered instability, identifying two possible fates: migration to nonultracompact configurations or collapse to bhs. in concrete examples we show that typical migration (collapse) timescales are not larger than ∼103 light-crossing times, unless the stable lr potential well is very shallow. our results show that the lr instability is effective in destroying horizonless ultracompact objects that could be plausible bh imitators. | exotic compact objects and the fate of the light-ring instability |
we present new measurements of rest-uv luminosity functions and angular correlation functions from 4,100,221 galaxies at z ~ 2-7 identified in the subaru/hyper suprime-cam survey and cfht large area u-band survey. the obtained luminosity functions at z ~ 4-7 cover a very wide uv luminosity range of ~ $0.002\mbox{--}2000{l}_{\mathrm{uv}}^{* }$ combined with previous studies, confirming that the dropout luminosity function is a superposition of the active galactic nucleus (agn) luminosity function dominant at m uv ≲ -24 mag and the galaxy luminosity function dominant at m uv ≳ -22 mag, consistent with galaxy fractions based on 1037 spectroscopically identified sources. galaxy luminosity functions estimated from the spectroscopic galaxy fractions show the bright-end excess beyond the schechter function at ≳2σ levels, possibly made by inefficient mass quenching, low dust obscuration, and/or hidden agn activity. by analyzing the correlation functions at z ~ 2-6 with hod models, we find a weak redshift evolution (within 0.3 dex) of the ratio of the star formation rate (sfr) to the dark matter accretion rate, $\mathrm{sfr}/{\dot{m}}_{{\rm{h}}}$ , indicating the almost constant star formation efficiency at z ~ 2-6, as suggested by our earlier work at z ~ 4-7. meanwhile, the ratio gradually increases with decreasing redshift at z < 5 within 0.3 dex, which quantitatively reproduces the cosmic sfr density evolution, suggesting that the redshift evolution is primarily driven by the increase of the halo number density due to the structure formation, and the decrease of the accretion rate due to the cosmic expansion. extrapolating this calculation to higher redshifts assuming the constant efficiency suggests a rapid decrease of the sfr density at z > 10 with ∝ 10-0.5(1+z), which will be directly tested with the james webb space telescope. | goldrush. iv. luminosity functions and clustering revealed with4,000,000 galaxies at z 2-7: galaxy-agn transition, star formation efficiency, and implication for evolution at z > 10 |
we report the discovery of eight new ultra-faint dwarf galaxy candidates in the second year of optical imaging data from the dark energy survey (des). six of these candidates are detected at high confidence, while two lower-confidence candidates are identified in regions of non-uniform survey coverage. the new stellar systems are found by three independent automated search techniques and are identified as overdensities of stars, consistent with the isochrone and luminosity function of an old and metal-poor simple stellar population. the new systems are faint (mv > -4.7 {mag}) and span a range of physical sizes (17 {pc} < r1/2 < 181 {pc}) and heliocentric distances (25 kpc < d⊙ < 214 kpc). all of the new systems have central surface brightnesses consistent with known ultra-faint dwarf galaxies (μ ≳ 27.5 {mag} {arcsec}-2). roughly half of the des candidates are more distant, less luminous, and/or have lower surface brightnesses than previously known milky way satellite galaxies. most of the candidates are found in the southern part of the des footprint close to the magellanic clouds. we find that the des data alone exclude (p < 10-3) a spatially isotropic distribution of milky way satellites and that the observed distribution can be well, though not uniquely, described by an association between several of the des satellites and the magellanic system. our model predicts that the full sky may hold ∼100 ultra-faint galaxies with physical properties comparable to the des satellites and that 20%-30% of these would be spatially associated with the magellanic clouds. | eight ultra-faint galaxy candidates discovered in year two of the dark energy survey |
the symmetry energy and its density dependence are crucial inputs for many nuclear physics and astrophysics applications, as they determine properties ranging from the neutron-skin thickness of nuclei to the crust thickness and the radius of neutron stars. recently, prex-ii reported a value of 0.283 ±0.071 fm for the neutron-skin thickness of 208pb, implying a slope parameter l =106 ±37 mev , larger than most ranges obtained from microscopic calculations and other nuclear experiments. we use a nonparametric equation of state representation based on gaussian processes to constrain the symmetry energy s0, l , and rskin 208pb directly from observations of neutron stars with minimal modeling assumptions. the resulting astrophysical constraints from heavy pulsar masses, ligo/virgo, and nicer clearly favor smaller values of the neutron skin and l , as well as negative symmetry incompressibilities. combining astrophysical data with prex-ii and chiral effective field theory constraints yields s0=33. 0-1.8+2.0 mev , l =5 3-15+14 mev , and rskin208pb =0.1 7-0.04+0.04 fm . | astrophysical constraints on the symmetry energy and the neutron skin of 208pb with minimal modeling assumptions |
we present a possible observing scenario for the advanced ligo and advanced virgo gravitational-wave detectors over the next decade, with the intention of providing information to the astronomy community to facilitate planning for multi-messenger astronomy with gravitational waves. we determine the expected sensitivity of the network to transient gravitational-wave signals, and study the capability of the network to determine the sky location of the source. we report our findings for gravitational-wave transients, with particular focus on gravitational-wave signals from the inspiral of binary neutron-star systems, which are considered the most promising for multi-messenger astronomy. the ability to localize the sources of the detected signals depends on the geographical distribution of the detectors and their relative sensitivity, and 90% credible regions can be as large as thousands of square degrees when only two sensitive detectors are operational. determining the sky position of a significant fraction of detected signals to areas of 5 deg2 to 20 deg2 will require at least three detectors of sensitivity within a factor of ∼ 2 of each other and with a broad frequency bandwidth. should the third ligo detector be relocated to india as expected, a significant fraction of gravitational-wave signals will be localized to a few square degrees by gravitational-wave observations alone. | prospects for observing and localizing gravitational-wave transients with advanced ligo and advanced virgo |
the discovery that at least some fast radio bursts (frbs) repeat has ruled out cataclysmic events as the progenitors of these particular bursts. frb 121102 is the most well-studied repeating frb but despite extensive monitoring of the source, no underlying pattern in the repetition has previously been identified. here, we present the results from a radio monitoring campaign of frb 121102 using the 76 m lovell telescope. using the pulses detected in the lovell data along with pulses from the literature, we report a detection of periodic behaviour of the source over the span of 5 yr of data. we predict that the source is currently 'off' and that it should turn 'on' for the approximate mjd range 59002-59089 (2020 june 2 to 2020 august 28). this result, along with the recent detection of periodicity from another repeating frb, highlights the need for long-term monitoring of repeating frbs at a high cadence. using simulations, we show that one needs at least 100 h of telescope time to follow-up repeating frbs at a cadence of 0.5-3 d to detect periodicities in the range of 10-150 d. if the period is real, it shows that repeating frbs can have a large range in their activity periods that might be difficult to reconcile with neutron star precession models. | possible periodic activity in the repeating frb 121102 |
we present emission-line measurements and physical interpretations for a sample of 117 [o iii] emitting galaxies at z = 5.33-6.93, using the first deep jwst/nircam wide-field slitless spectroscopic observations. our 9.7 hr integration is centered upon the z = 6.3 quasar j0100+2802-the first of six fields targeted by the eiger survey-and covers λ = 3-4 μm. we detect 133 [o iii] doublets, but close pairs motivated by their small scale clustering excess. the galaxies are characterized by a uv luminosity m uv ~ -19.6 (-17.7 to -22.3), stellar mass ~108 (106.8-10.1) m ⊙, hβ and [o iii]4960+5008 ews ≈ 850 å (up to 3000 å), young ages, a highly excited interstellar medium, and low dust attenuations. these high ews are very rare in the local universe, but we show they are ubiquitous at z ~ 6 based on the measured number densities. the stacked spectrum reveals hγ and [o iii]4364, which shows that the galaxies are typically dust- and metal-poor (e (b - v) = 0.1, $12+\mathrm{log}({\rm{o}}/{\rm{h}})=7.4$ ) with a high electron temperature (2 × 104 k) and a production efficiency of ionizing photons (ξ ion = 1025.3 hz erg-1). we further show the existence of a strong mass-metallicity relation. the properties of the stars and gas in z ~ 6 galaxies conspire to maximize the [o iii] output from galaxies, yielding an [o iii] luminosity density at z ≈ 6 that is significantly higher than that at z ≈ 2. thus, [o iii] emission-line surveys with jwst prove a highly efficient method to trace the galaxy density in the epoch of reionization. | eiger. ii. first spectroscopic characterization of the young stars and ionized gas associated with strong hβ and [o iii] line emission in galaxies at z = 5-7 with jwst |
the all-sky automated survey for supernovae (asas-sn) is the first optical survey to routinely monitor the whole sky with a cadence of ∼2-3 d down to v ≲ 17 mag. asas-sn has monitored the whole sky since 2014, collecting ∼100-500 epochs of observations per field. the v-band light curves for candidate variables identified during the search for supernovae are classified using a random forest classifier and visually verified. we present a catalogue of 66 179 bright, new variable stars discovered during our search for supernovae, including 27 479 periodic variables and 38 700 irregular variables. v-band light curves for the asas-sn variables are available through the asas-sn variable stars data base (https://asas-sn.osu.edu/variables). the data base will begin to include the light curves of known variable stars in the near future along with the results for a systematic, all-sky variability survey. | the asas-sn catalogue of variable stars i: the serendipitous survey |
the formation and evolution of binary stars are critical components of several fields in astronomy. the most numerous sources for gravitational wave observatories are inspiraling or merging compact binaries, while binary stars are present in nearly every electromagnetic survey regardless of the target population. simulations of large binary populations serve to both predict and inform observations of electromagnetic and gravitational wave sources. binary population synthesis is a tool that balances physical modeling with simulation speed to produce large binary populations on timescales of days. we present a community-developed binary population synthesis suite, cosmic, which is designed to simulate compact-object binary populations and their progenitors. as a proof of concept, we simulate the galactic population of compact binaries and their gravitational wave signals observable by the laser interferometer space antenna. | cosmic variance in binary population synthesis |
we report the discovery of rising x-ray emission from the binary neutron star merger event gw170817. this is the first detection of x-ray emission from a gravitational-wave (gw) source. observations acquired with the chandra x-ray observatory (cxo) at t≈ 2.3 days post-merger reveal no significant emission, with {l}x≲ 3.2× {10}38 {erg} {{{s}}}-1 (isotropic-equivalent). continued monitoring revealed the presence of an x-ray source that brightened with time, reaching {l}x≈ 9× {10}38 {erg} {{{s}}}-1 at ≈ 15.1 days post-merger. we interpret these findings in the context of isotropic and collimated relativistic outflows (both on- and off-axis). we find that the broadband x-ray to radio observations are consistent with emission from a relativistic jet with kinetic energy {e}k∼ {10}49-50 {erg}, viewed off-axis with {θ }{obs}∼ 20^\circ {--}40^\circ . our models favor a circumbinary density n∼ {10}-4{--}{10}-2 {{cm}}-3, depending on the value of the microphysical parameter {ɛ }b={10}-4{--}{10}-2. a central-engine origin of the x-ray emission is unlikely. future x-ray observations at t≳ 100 days, when the target will be observable again with the cxo, will provide additional constraints to solve the model degeneracies and test our predictions. our inferences on {θ }{obs} are testable with gw information on gw170817 from advanced ligo/virgo on the binary inclination. | the electromagnetic counterpart of the binary neutron star merger ligo/virgo gw170817. v. rising x-ray emission from an off-axis jet |
during the second observing run of the laser interferometer gravitational-wave observatory (ligo) and virgo interferometer, a gravitational-wave signal consistent with a binary neutron star coalescence was detected on 2017 august 17th (gw170817), quickly followed by a coincident short gamma-ray burst trigger detected by the fermi satellite. the distance less than 40 (dlt40) mpc supernova search performed pointed follow-up observations of a sample of galaxies regularly monitored by the survey that fell within the combined ligo+virgo localization region and the larger fermi gamma-ray burst error box. here we report the discovery of a new optical transient (dlt17ck, also known as sss17a; it has also been registered as at 2017gfo) spatially and temporally coincident with gw170817. the photometric and spectroscopic evolution of dlt17ck is unique, with an absolute peak magnitude of mr= -15.8 ± 0.1 and an r-band decline rate of 1.1 mag day-1. this fast evolution is generically consistent with kilonova models, which have been predicted as the optical counterpart to binary neutron star coalescences. analysis of archival dlt40 data does not show any sign of transient activity at the location of dlt17ck down to r ∼ 19 mag in the time period between 8 months and 21 days prior to gw170817. this discovery represents the beginning of a new era for multi-messenger astronomy, opening a new path by which to study and understand binary neutron star coalescences, short gamma-ray bursts, and their optical counterparts. | the discovery of the electromagnetic counterpart of gw170817: kilonova at 2017gfo/dlt17ck |
we propose a space-based interferometer surveying the gravitational wave (gw) sky in the milli-hz to μ-hz frequency range. by the 2040s, the μ-hz frequency band, bracketed in between the laser interferometer space antenna (lisa) and pulsar timing arrays, will constitute the largest gap in the coverage of the astrophysically relevant gw spectrum. yet many outstanding questions related to astrophysics and cosmology are best answered by gw observations in this band. we show that a μ-hz gw detector will be a truly overarching observatory for the scientific community at large, greatly extending the potential of lisa. conceived to detect massive black hole binaries from their early inspiral with high signal-to-noise ratio, and low-frequency stellar binaries in the galaxy, this instrument will be a cornerstone for multimessenger astronomy from the solar neighbourhood to the high-redshift universe. | unveiling the gravitational universe at μ-hz frequencies |
we explore scenarios for reionizing the intergalactic medium with low galaxy ionizing photon escape fractions. we combine simulation-based halo mass-dependent escape fractions with an extrapolation of the observed galaxy rest-ultraviolet luminosity functions to solve for the reionization history from z = 20\to 4. we explore the posterior distributions for key unknown quantities, including the limiting halo mass for star formation, the ionizing photon production efficiency, and a potential contribution from active galactic nuclei (agns). we marginalize over the allowable parameter space using a markov chain monte carlo method, finding a solution that satisfies the most model-independent constraints on reionization. our fiducial model can match observational constraints with an average escape fraction of <5% throughout the bulk of the epoch of reionization if (i) galaxies form stars down to the atomic cooling limit before reionization and a photosuppression mass of log(m h/m ⊙) ∼ 9 during/after reionization (-13 < m uv,lim < -11), (ii) galaxies become more efficient producers of ionizing photons at higher redshifts and fainter magnitudes, and (iii) there is a significant but subdominant contribution by agns at z ≲ 7. in this model, the faintest galaxies (m uv > -15) dominate the ionizing emissivity, leading to an earlier start to reionization and a smoother evolution of the ionized volume-filling fraction than models that assume a single escape fraction at all redshifts and luminosities. the ionizing emissivity from this model is consistent with observations at z = 4-5 (and below, when extrapolated), in contrast to some models that assume a single escape fraction. our predicted ionized volume-filling fraction at z = 7 of {q}{{{h}}ii}} = 78% (±8%) is in modest (∼1σ-2σ) tension with observations of lyα emitters at z ∼ 7 and the damping-wing analyses of the two known z > 7 quasars, which prefer {q}{{{h}}ii},z=7} ∼ 40%-50%. | conditions for reionizing the universe with a low galaxy ionizing photon escape fraction |
we present an analysis of all prime hst legacy fields spanning >800 arcmin2 in the search for z ∼ 10 galaxy candidates and the study of their uv luminosity function (lf). in particular, we present new z ∼ 10 candidates selected from the full hubble frontier field (hff) data set. despite the addition of these new fields, we find a low abundance of z ∼ 10 candidates with only nine reliable sources identified in all prime hst data sets that include the hudf09/12, the hudf/xdf, all of the candels fields, and now the hff survey. based on this comprehensive search, we find that the uv luminosity function decreases by one order of magnitude from z ∼ 8 to z ∼ 10 over a four-magnitude range. this also implies a decrease of the cosmic star formation rate density by an order of magnitude within 170 myr from z ∼ 8 to z ∼ 10. we show that this accelerated evolution compared to lower redshift can entirely be explained by the fast build up of the dark matter halo mass function at z > 8. consequently, the predicted uv lfs from several models of galaxy formation are in good agreement with this observed trend, even though the measured uv lf lies at the low end of model predictions. the difference is generally still consistent within the poisson and cosmic variance uncertainties. we discuss the implications of these results in light of the upcoming james webb space telescope mission, which is poised to find much larger samples of z ∼ 10 galaxies as well as their progenitors at less than 400 myr after the big bang. based on data obtained with the hubble space telescope operated by aura, inc. for nasa under contract nas5-26555. | the dearth of z ∼ 10 galaxies in all hst legacy fields—the rapid evolution of the galaxy population in the first 500 myr |
the binary neutron star (bns) merger gw170817 was the first astrophysical source detected in gravitational waves and multiwavelength electromagnetic radiation. the almost simultaneous observation of a pulse of gamma rays proved that bns mergers are associated with at least some short gamma-ray bursts (grbs). however, the gamma-ray pulse was faint, casting doubt on the association of bns mergers with the luminous, highly relativistic outflows of canonical short grbs. here we show that structured jets with a relativistic, energetic core surrounded by slower and less energetic wings produce afterglow emission that brightens characteristically with time, as recently seen in the afterglow of gw170817. initially, we only see the relatively slow material moving towards us. as time passes, larger and larger sections of the outflow become visible, increasing the luminosity of the afterglow. the late appearance and increasing brightness of the multiwavelength afterglow of gw170817 allow us to constrain the geometry of its ejecta and thus reveal the presence of an off-axis jet pointing about 30° away from earth. our results confirm a single origin for bns mergers and short grbs: gw170817 produced a structured outflow with a highly relativistic core and a canonical short grb. we did not see the bright burst because it was beamed away from earth. however, approximately one in 20 mergers detected in gravitational waves will be accompanied by a bright, canonical short grb. | late time afterglow observations reveal a collimated relativistic jet in the ejecta of the binary neutron star merger gw170817 |
we explore a newly proposed channel to create binary black holes of stellar origin. this scenario applies to massive, tight binaries where mixing induced by rotation and tides transports the products of hydrogen burning throughout the stellar envelopes. this slowly enriches the entire star with helium, preventing the build-up of an internal chemical gradient. the stars remain compact as they evolve nearly chemically homogeneously, eventually forming two black holes, which we estimate typically merge 4-11 gyr after formation. like other proposed channels, this evolutionary pathway suffers from significant theoretical uncertainties, but could be constrained in the near future by data from advanced ground-based gravitational-wave detectors. we perform monte carlo simulations of the expected merger rate over cosmic time to explore the implications and uncertainties. our default model for this channel yields a local binary black hole merger rate of about 10 gpc-3 yr-1 at redshift z = 0, peaking at twice this rate at z = 0.5. this means that this channel is competitive, in terms of expected rates, with the conventional formation scenarios that involve a common-envelope phase during isolated binary evolution or dynamical interaction in a dense cluster. the events from this channel may be distinguished by the preference for nearly equal-mass components and high masses, with typical total masses between 50 and 110 m⊙. unlike the conventional isolated binary evolution scenario that involves shrinkage of the orbit during a common-envelope phase, short time delays are unlikely for this channel, implying that we do not expect mergers at high redshift. | merging binary black holes formed through chemically homogeneous evolution in short-period stellar binaries |
measurements of neutron star masses, radii, and tidal deformability have direct connections to nuclear physics via the equation of state (eos), which for the cold, catalyzed matter in neutron star cores is commonly represented as the pressure as a function of energy density. microscopic models with exotic degrees of freedom display nontrivial structure in the speed of sound ($c_s$) in the form of first-order phase transitions and bumps, oscillations, and plateaus in the case of crossovers and higher-order phase transitions. we present a procedure based on gaussian processes to generate an ensemble of eoss that include nontrivial features. using a bayesian analysis incorporating measurements from x-ray sources, gravitational wave observations, and perturbative qcd results, we show that these features are compatible with current constraints. we investigate the possibility of a global maximum in $c_s$ that occurs within the densities realized in neutron stars -- implying a softening of the eos and possibly an exotic phase in the core of massive stars -- and find that such a global maximum is consistent with, but not required by, current constraints. | nontrivial features in the speed of sound inside neutron stars |
we report {\em jwst}/nircam measurements of quasar host galaxy emissions and supermassive black hole (smbh) masses for six quasars at $5.9<z<7.1$ in the \textit{emission-line galaxies and intergalactic gas in the epoch of reionization} (eiger) project. we obtain deep nircam imaging in the f115w, f200w, and f356w bands, as well as f356w grism spectroscopy of the quasars. we use bright unsaturated stars to construct models of the point spread function (psf) and estimate the errors of these psfs. we then measure or constrain the fluxes and morphology of the quasar host galaxies by fitting the quasar images as a point source plus an exponential disk. we successfully detect the host galaxy of three quasars, which have host-to-quasar flux ratios of $\sim1\%-5\%$. spectral energy distribution (sed) fitting suggests that these quasar host galaxies have stellar masses of $m_*\gtrsim10^{10}m_\odot$. for quasars with host galaxy non-detections, we estimate the upper limits of their stellar masses. we use the grism spectra to measure the {\hb} line profile and the continuum luminosity, then estimate the smbh masses for the quasars. our results indicate that the positive relation between smbh masses and host galaxy stellar masses already exists at redshift $z\gtrsim6$. the quasars in our sample show a high black hole to stellar mass ratio of $m_\text{bh}/m_*\sim0.15$, which is about $\sim1-2$ dex higher than the local relations. this result suggests that luminous quasars at $z\gtrsim6$ form a biased sample with overmassive black holes, which might have experienced early smbh growth compared to their host galaxies' star formation. | eiger v. characterizing the host galaxies of luminous quasars at $z\\gtrsim6$ |
jwst observations confirm the existence of galaxies as early as 300myr and at a higher number density than expected based on galaxy formation models and hst observations. yet, sources confirmed spectroscopically in the first 500myr have estimated stellar masses $<5\times10^8m_\odot$, limiting the signal to noise ratio (snr) for investigating substructure. we present a high-resolution spectroscopic and spatially resolved study of a rare bright galaxy at $z=9.3127\pm0.0002$ with a stellar mass of $(2.5^{+0.7}_{-0.5})\times10^9m_\odot$, forming $25^{+3}_{-4}m_\odot/yr$ and with a metallicity of $\sim0.1z_\odot$- lower than in the local universe for the stellar mass but in line with expectations of chemical enrichment in galaxies 1-2gyr after the big bang. the system has a morphology typically associated to two interacting galaxies, with a two-component main clump of very young stars (age$<10$myr) surrounded by an extended stellar population ($130\pm20$myr old, identified by modeling the nirspec spectrum) and an elongated clumpy tidal tail. the spectroscopic observations identify o, ne and h emission lines, and the lyman break, where there is evidence of substantial ly$\alpha$ absorption. the [oii] doublet is resolved spectrally, enabling an estimate of the electron number density and ionization parameter of the interstellar medium and showing higher densities and ionization than in lower redshift analogs. for the first time at $z>8$, we identify evidence of absorption lines (si, c and fe), with low confidence individual detections but snr$>6$ when stacked. the absorption features suggest that ly$\alpha$ is damped by the interstellar and circumgalactic medium. our observations provide evidence of rapid efficient build-up of mass and metals in the immediate aftermath of the big bang through mergers, demonstrating that massive galaxies with several billion stars exist earlier than expected. | a massive interacting galaxy 525 million years after the big bang |
neutron-star cores contain matter at the highest densities in our universe. this highly compressed matter may undergo a phase transition where nuclear matter melts into deconfined quark matter, liberating its constituent quarks and gluons. quark matter exhibits an approximate conformal symmetry, predicting a specific form for its equation of state (eos), but it is currently unknown whether the transition takes place inside at least some physical neutron stars. here, we quantify this likelihood by combining information from astrophysical observations and theoretical calculations. using bayesian inference, we demonstrate that in the cores of maximally massive stars, the eos is consistent with quark matter. we do this by establishing approximate conformal symmetry restoration with high credence at the highest densities probed and demonstrating that the number of active degrees of freedom is consistent with deconfined matter. the remaining likelihood is observed to correspond to eoss exhibiting phase-transition-like behavior, treated as arbitrarily rapid crossovers in our framework. | strongly interacting matter exhibits deconfined behavior in massive neutron stars |
recent observations identify a valley in the radius distribution of small exoplanets, with planets in the range 1.5-2.0 r⊕ significantly less common than somewhat smaller or larger planets. this valley may suggest a bimodal population of rocky planets that are either engulfed by massive gas envelopes that significantly enlarge their radius, or do not have detectable atmospheres at all. one explanation of such a bimodal distribution is atmospheric erosion by high-energy stellar photons. we investigate an alternative mechanism: the luminosity of the cooling rocky core, which can completely erode light envelopes while preserving heavy ones, produces a deficit of intermediate sized planets. we evolve planetary populations that are derived from observations using a simple analytical prescription, accounting self-consistently for envelope accretion, cooling and mass-loss, and demonstrate that core-powered mass-loss naturally reproduces the observed radius distribution, regardless of the high-energy incident flux. observations of planets around different stellar types may distinguish between photoevaporation, which is powered by the high-energy tail of the stellar radiation, and core-powered mass-loss, which depends on the bolometric flux through the planet's equilibrium temperature that sets both its cooling and mass-loss rates. | core-powered mass-loss and the radius distribution of small exoplanets |
we present the second open gravitational-wave catalog (2-ogc) of compact-binary coalescences, obtained from the complete set of public data from advanced ligo's first and second observing runs. for the first time we also search public data from the virgo observatory. the sensitivity of our search benefits from updated methods of ranking candidate events including the effects of nonstationary detector noise and varying network sensitivity; in a separate targeted binary black hole merger search we also impose a prior distribution of binary component masses. we identify a population of 14 binary black hole merger events with probability of astrophysical origin >0.5 as well as the binary neutron star merger gw170817. we confirm the previously reported events gw170121, gw170304, and gw170727 and also report gw151205, a new marginal binary black hole merger with a primary mass of {67}-17+28 m⊙ that may have formed through hierarchical merger. we find no additional significant binary neutron star merger or neutron star-black hole merger events. to enable deeper follow-up as our understanding of the underlying populations evolves, we make available our comprehensive catalog of events, including the subthreshold population of candidates and posterior samples from parameter inference of the 30 most significant binary black hole candidates. | 2-ogc: open gravitational-wave catalog of binary mergers from analysis of public advanced ligo and virgo data |
gw170817 was the first gravitational-wave detection of a binary neutron-star merger. it was accompanied by radiation across the electromagnetic spectrum and localized to the galaxy ngc 4993 at a distance of 40 megaparsecs. it has been proposed that the observed γ-ray, x-ray and radio emission is due to an ultra-relativistic jet being launched during the merger (and successfully breaking out of the surrounding material), directed away from our line of sight (off-axis). the presence of such a jet is predicted from models that posit neutron-star mergers as the drivers of short hard-γ-ray bursts. here we report that the radio light curve of gw170817 has no direct signature of the afterglow of an off-axis jet. although we cannot completely rule out the existence of a jet directed away from the line of sight, the observed γ-ray emission could not have originated from such a jet. instead, the radio data require the existence of a mildly relativistic wide-angle outflow moving towards us. this outflow could be the high-velocity tail of the neutron-rich material that was ejected dynamically during the merger, or a cocoon of material that breaks out when a jet launched during the merger transfers its energy to the dynamical ejecta. because the cocoon model explains the radio light curve of gw170817, as well as the γ-ray and x-ray emission (and possibly also the ultraviolet and optical emission), it is the model that is most consistent with the observational data. cocoons may be a ubiquitous phenomenon produced in neutron-star mergers, giving rise to a hitherto unidentified population of radio, ultraviolet, x-ray and γ-ray transients in the local universe. | a mildly relativistic wide-angle outflow in the neutron-star merger event gw170817 |
we present the first constraints on the prevalence of z > 10 galaxies in the hubble ultra deep field (hudf) leveraging new nircam observations from jems (jwst extragalactic medium-band survey). these nircam observations probe redward of 1.6 μm, beyond the wavelength limit of hst, allowing us to search for galaxies to z > 10. these observations indicate that the highest redshift candidate identified in the hudf09 data with hst, udfj-39546284, has a redshift of z > 11.5, as had been suggested in analyses of the hudf12/xdf data. this has now been confirmed with jwst nirspec. this source is thus the most distant galaxy discovered by hst in its >30 yr of operation. additionally, we identify nine other z ~ 8-13 candidate galaxies over the hudf, two of which are new discoveries that appear to lie at z ~ 11-12. we use these results to characterize the evolution of the uv luminosity function (lf) from z ~ 15 to z ~ 8.7. while our lf results at z ~ 8.7 and z ~ 10.5 are consistent with previous findings over the hudf, our new lf estimates at z ~ 12.6 are higher than other results in the literature, potentially pointing to a milder evolution in the uv luminosity density from z ~ 12.6. we emphasize that our lf results are uncertain given the small number of z ~ 12.6 sources and limited volume probed. the new nircam data also indicate that the faint z ~ 8-13 galaxies in the hudf/xdf show blue uv-continuum slopes β ~ -2.7, high specific star formation rates ~24.5 gyr-1, and high ew (~1300 å) [o iii] + h β emission, with two z ~ 8.5 sources showing [o iii] + h β ews of ~2300 å. | evolution of the uv lf from z 15 to z 8 using new jwst nircam medium-band observations over the hudf/xdf |
we review recent developments and results in testing general relativity (gr) at cosmological scales. the subject has witnessed rapid growth during the last two decades with the aim of addressing the question of cosmic acceleration and the dark energy associated with it. however, with the advent of precision cosmology, it has also become a well-motivated endeavor by itself to test gravitational physics at cosmic scales. we overview cosmological probes of gravity, formalisms and parameterizations for testing deviations from gr at cosmological scales, selected modified gravity (mg) theories, gravitational screening mechanisms, and computer codes developed for these tests. we then provide summaries of recent cosmological constraints on mg parameters and selected mg models. we supplement these cosmological constraints with a summary of implications from the recent binary neutron star merger event. next, we summarize some results on mg parameter forecasts with and without astrophysical systematics that will dominate the uncertainties. the review aims at providing an overall picture of the subject and an entry point to students and researchers interested in joining the field. it can also serve as a quick reference to recent results and constraints on testing gravity at cosmological scales. | testing general relativity in cosmology |
the two recent gravitational-wave events gw190425 and gw190814 from the third observing run of ligo/virgo have both a companion which is unexpected if originated from a neutron star or a stellar black hole, with masses $[1.6-2.5]~m_\odot$ and $[2.5-2.7]~m_\odot$ and merging rates $ 460^{+1050}_{-360} $ and $ 7^{+16}_{-6}$ events/yr/gpc$^3$ respectively, at 90\% c.l.. moreover, the recent event gw190521 has black hole components with masses 67 and $91~m_\odot$, and therefore lies in the so-called pair-instability mass gap, where there should not be direct formation of stellar black holes. the possibility that all of these compact objects are primordial black holes (pbhs) is investigated. the known thermal history of the universe predicts that pbh formation is boosted at the time of the qcd transition, inducing a peak in their distribution at this particular mass scale, and a bump around $30-50~m_\odot$. we find that the merging rates inferred from gw190425, gw190521 and gw190814 are consistent with pbh binaries formed by capture in dense halos in the matter era or in the early universe. at the same time, the rate of black hole mergers around $30~m_\odot$ and of sub-solar pbh mergers do not exceed the ligo/virgo limits. such pbhs could explain a significant fraction, or even the totality of the dark matter, but they must be sufficiently strongly clustered in order to be consistent with current astrophysical limits. | gw190425, gw190521 and gw190814: three candidate mergers of primordial black holes from the qcd epoch |
we establish that massive complex abelian vector fields (mass μ) can form gravitating solitons, when minimally coupled to einstein's gravity. such proca stars (pss) have a stationary, everywhere regular and asymptotically flat geometry. the proca field, however, possesses a harmonic time dependence (frequency w), realizing wheeler's concept of geons for an abelian spin 1 field. we obtain pss with both a spherically symmetric (static) and an axially symmetric (stationary) line element. the latter form a countable number of families labelled by an integer m ∈z+. pss, like (scalar) boson stars, carry a conserved noether charge, and are akin to the latter in many ways. in particular, both types of stars exist for a limited range of frequencies and there is a maximal adm mass, mmax, attained for an intermediate frequency. for spherically symmetric pss (rotating pss with m = 1 , 2 , 3), mmax ≃ 1.058 mpl2 / μ (mmax ≃ 1.568 , 2.337 , 3.247 mpl2 / μ), slightly larger values than those for (mini-)boson stars. we establish perturbative stability for a subset of solutions in the spherical case and anticipate a similar conclusion for fundamental modes in the rotating case. the discovery of pss opens many avenues of research, reconsidering five decades of work on (scalar) boson stars, in particular as possible dark matter candidates. | proca stars: gravitating bose-einstein condensates of massive spin 1 particles |
we present the next generation deep extragalactic exploratory public (ngdeep) survey, a deep slitless spectroscopic and imaging cycle 1 jwst treasury survey designed to constrain feedback mechanisms in low-mass galaxies across cosmic time. ngdeep targets the hubble ultra deep field (hudf) with niriss slitless spectroscopy (f~1.2e-18 erg/s/cm^2, 5sigma) to measure metallicities and star-formation rates (sfrs) for low-mass galaxies through the peak of the cosmic sfr density (0.5<z<4). in parallel, ngdeep targets the hudf-par2 parallel field with nircam (m=30.6-30.9, 5sigma) to discover galaxies to z>12, constraining the slope of the faint-end of the rest-ultraviolet luminosity function. ngdeep overlaps with the deepest hst acs optical imaging in the sky: f435w in the hudf (m=29.6), and f814w in hudf-par2 (m=30), making this a premier hst+jwst deep field. as a treasury survey, ngdeep data is public immediately, and we will rapidly release data products and catalogs in the spirit of previous deep field initiatives. in this paper we present the ngdeep survey design, summarize the science goals, and detail plans for the public release of ngdeep reduced data products. | the next generation deep extragalactic exploratory public (ngdeep) survey |
the recently established formalism of a worldline quantum field theory, which describes the classical scattering of massive bodies (black holes, neutron stars, or stars) in einstein gravity, is generalized up to quadratic order in spin, revealing an alternative n =2 supersymmetric description of the symmetries inherent in spinning bodies. the far-field time domain waveform of the gravitational waves produced in such a spinning encounter is computed at leading order in the post-minkowskian (weak field, but generic velocity) expansion, and exhibits this supersymmetry. from the waveform we extract the leading-order total radiated angular momentum in a generic reference frame, and the total radiated energy in the center-of-mass frame to leading order in a low-velocity approximation. | gravitational bremsstrahlung and hidden supersymmetry of spinning bodies |
context. the multiplicity fraction of stars, down to the substellar regime, is a parameter of fundamental importance for stellar formation, evolution, and planetology. the census of multiple stars in the solar neighborhood is however incomplete.aims: our study is aimed at detecting companions of hipparcos catalog stars from the proper motion anomaly (pma) they induce on their host star, namely, the difference between their long-term hipparcos-gaia and short-term gaia proper motion vectors. we also aim to detect resolved, gravitationally bound companions of the hipparcos catalog stars (117 955 stars) and of the gaia edr3 stars closer than 100 pc (542 232 stars).methods: using the hipparcos and edr3 data, we revised the pma catalog for the hipparcos stars. in order to identify gravitationally bound visual companions of our sample, we searched the gaia edr3 catalog for common proper-motion (cpm) candidates.results: the detection of tangential velocity anomalies with a median accuracy of σ(δvt) = 26 cm s−1 per parsec of distance is demonstrated with the edr3. this improvement by a factor 2.5 in accuracy, as compared to gaia dr2, results in pma detection limits on companions that are well into the planetary mass regime for many targets. we identify 37 515 hipparcos stars presenting a pma at significant level (s/n > 3), namely, a fraction of 32% (compared to 30% for the dr2) and 12 914 (11%) hosting cpm bound candidate companions. after including the gaia edr3 renormalised unit weight error (ruwe > 1.4) as an additional indicator, 50 720 stars of the hipparcos catalog (43%) exhibit at least one signal of binarity. among the gaia edr3 stars located within 100 pc, we find cpm bound candidate companions for 39 490 stars (7.3% of the sample).conclusions: the search for companions using a combination of the pma, cpm, and ruwe indicators significantly improves the exhaustivity of the multiplicity survey. the detection of cpm companions of very bright stars (heavily saturated on the gaia detectors) that are classical benchmark objects for stellar physics provides a useful proxy for estimating their distance with a higher accuracy than with hipparcos. full tables a.1-a.3 are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/657/a7 | stellar and substellar companions from gaia edr3. proper-motion anomaly and resolved common proper-motion pairs |
we present the open supernova catalog, an online collection of observations and metadata for presently 36,000+ supernovae and related candidates. the catalog is freely available on the web (https://sne.space), with its main interface having been designed to be a user-friendly, rapidly searchable table accessible on desktop and mobile devices. in addition to the primary catalog table containing supernova metadata, an individual page is generated for each supernova, which displays its available metadata, light curves, and spectra spanning x-ray to radio frequencies. the data presented in the catalog is automatically rebuilt on a daily basis and is constructed by parsing several dozen sources, including the data presented in the supernova literature and from secondary sources such as other web-based catalogs. individual supernova data is stored in the hierarchical, human- and machine-readable json format, with the entirety of each supernova’s data being contained within a single json file bearing its name. the setup we present here, which is based on open-source software maintained via git repositories hosted on github, enables anyone to download the entirety of the supernova data set to their home computer in minutes, and to make contributions of their own data back to the catalog via git. as the supernova data set continues to grow, especially in the upcoming era of all-sky synoptic telescopes, which will increase the total number of events by orders of magnitude, we hope that the catalog we have designed will be a valuable tool for the community to analyze both historical and contemporary supernovae. | an open catalog for supernova data |
matter in neutron star collisions reaches densities up to few times the nuclear saturation threshold, ρ0 and temperatures up to one hundred mev. understanding the structure and composition of such matter requires many-body non-perturbative calculations that are currently highly uncertain. unique constraints on the neutron star matter are provided by gravitational-wave observations aided by numerical relativity simulations. in this work, we explore the thermodynamical conditions of matter along the merger dynamics. we consider 3 microphysical equations of state and numerical relativity simulations including approximate neutrino transport. the neutron star cores collision and their multiple bounces heat the initially cold matter to several tens of mev. streams of hot matter with initial densities ∼1 -2 ρ0 move outwards and cool due to decompression and neutrino emission. the merger can result in a neutron star remnant with densities up to 3 -5 ρ0 and temperatures ∼50 mev. the highest temperatures are confined in an approximately spherical annulus at densities ∼ρ0 . such temperatures favour positron-neutron capture thus leading to a neutrino emission dominated by electron antineutrinos. we study the impact of trapped neutrinos on the remnant matter's pressure, electron fraction and temperature and find that it has a negligible effect. disks around neutron star or black hole remnant are neutron rich and not isentropic, but they differ in size, entropy and lepton fraction depending on the nature of the central object. in the presence of a black hole, disks are smaller and mostly transparent to neutrinos; in presence of a massive neutron star, they are more massive, geometrically and optically thick. | thermodynamics conditions of matter in neutron star mergers |
we report the identification of 15 galaxy candidates at $z\ge9$ using the initial cosmos-web jwst observations over 77 arcmin$^2$ through four nircam filters (f115w, f150w, f277w, f444w) with an overlap with miri (f770w) of 8.7 arcmin$^2$. we fit the sample using several publicly-available sed fitting and photometric redshift codes and determine their redshifts between $z=9.3$ and $z=10.9$ ($\langle z\rangle=10.0$), uv-magnitudes between m$_{\rm uv}$ = $-$21.2 and $-$19.5 (with $\langle $m$_{\rm uv}\rangle=-20.2$) and rest-frame uv slopes ($\langle \beta\rangle=-2.4$). these galaxies are, on average, more luminous than most $z\ge9$ candidates discovered by jwst so far in the literature, while exhibiting similar blue colors in their rest-frame uv. the rest-frame uv slopes derived from sed-fitting are blue ($\beta\sim$[$-$2.0, $-$2.7]) without reaching extremely blue values as reported in other recent studies at these redshifts. the blue color is consistent with models that suggest the underlying stellar population is not yet fully enriched in metals like similarly luminous galaxies in the lower redshift universe. the derived stellar masses with $\langle \log_{\rm 10} ($m$_\star/$m$_\odot)\rangle\approx8-9$ are not in tension with the standard $\lambda$cdm model and our measurement of the volume density of such uv luminous galaxies aligns well with previously measured values presented in the literature at $z\sim9-10$. our sample of galaxies, although compact, are significantly resolved. | unveiling the distant universe: characterizing $z\\ge9$ galaxies in the first epoch of cosmos-web |
we present a three-dimensional map of interstellar dust reddening, covering three-quarters of the sky out to a distance of several kiloparsecs, based on pan-starrs 1 (ps1) and 2mass photometry. the map reveals a wealth of detailed structure, from filaments to large cloud complexes. the map has a hybrid angular resolution, with most of the map at an angular resolution of 3\buildrel{ \prime}\over{.} 4-13\buildrel{ \prime}\over{.} 7, and a maximum distance resolution of ∼ 25%. the three-dimensional distribution of dust is determined in a fully probabilistic framework, yielding the uncertainty in the reddening distribution along each line of sight, as well as stellar distances, reddenings, and classifications for 800 million stars detected by ps1. we demonstrate the consistency of our reddening estimates with those of two-dimensional emission-based maps of dust reddening. in particular, we find agreement with the planck {τ }353{ghz}-based reddening map to within 0.05 {mag} in e(b-v) to a depth of 0.5 {mag}, and explore systematics at reddenings less than e(b-v)≈ 0.08 {mag}. we validate our per-star reddening estimates by comparison with reddening estimates for stars with both sloan digital sky survey photometry and sloan extension for galactic understanding and exploration spectral classifications, finding per-star agreement to within 0.1 {mag} out to a stellar e(b-v) of 1 mag. we compare our map to two existing three-dimensional dust maps, by marshall et al. and lallement et al., demonstrating our finer angular resolution, and better distance resolution compared to the former within ∼ 3 {kpc}. the map can be queried or downloaded at http://argonaut.skymaps.info. we expect the three-dimensional reddening map presented here to find a wide range of uses, among them correcting for reddening and extinction for objects embedded in the plane of the galaxy, studies of galactic structure, calibration of future emission-based dust maps, and determining distances to objects of known reddening. | a three-dimensional map of milky way dust |
deep observations with the james webb space telescope (jwst) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black hole seeds and observed quasars. in this work, we present a jwst/nirspec spectrum from the jwst cycle 1 uncover treasury survey of a massive accreting black hole at z = 8.50 displaying a clear broad-line component as inferred from the hβ line with fwhm = 3439 ± 413 km s-1, typical of the broad-line region of an active galactic nucleus (agn). the agn nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. we compute a black hole mass of ${\mathrm{log}}_{10}({m}_{\mathrm{bh}}/{m}_{\odot })=8.17\pm 0.42$ and a bolometric luminosity of l bol ~ 6.6 × 1045 erg s-1. these values imply that our object is accreting at ~40% of the eddington limit. detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from alma, indicate an upper limit on the stellar mass of ${\mathrm{log}}_{10}({m}_{* }/{m}_{\odot })\lt 8.7$ , which would lead to an unprecedented ratio of black hole to host mass of at least ~30%. this is orders of magnitude higher compared to the local qsos but consistent with recent agn studies at high redshift with jwst. this finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-eddington rate at high redshift. given the predicted number densities of high-z faint agn, future nirspec observations of larger samples will allow us to further investigate galaxy-black hole coevolution in the early universe. | uncover: a nirspec identification of a broad-line agn at z = 8.50 |
we present a high-precision radial velocity (rv) survey of 719 fgkm stars, which host 164 known exoplanets and 14 newly discovered or revised exoplanets and substellar companions. this catalog updated the orbital parameters of known exoplanets and long-period candidates, some of which have decades-longer observational baselines than they did upon initial detection. the newly discovered exoplanets range from warm sub-neptunes and super-earths to cold gas giants. we present the catalog sample selection criteria, as well as over 100,000 rv measurements, which come from the keck-hires, apf-levy, and lick-hamilton spectrographs. we introduce the new rv search pipeline rvsearch (https://california-planet-search.github.io/rvsearch/) that we used to generate our planet catalog, and we make it available to the public as an open-source python package. this paper is the first study in a planned series that will measure exoplanet occurrence rates and compare exoplanet populations, including studies of giant planet occurrence beyond the water ice line, and eccentricity distributions to explore giant planet formation pathways. we have made public all radial velocities and associated data that we use in this catalog. | the california legacy survey. i. a catalog of 178 planets from precision radial velocity monitoring of 719 nearby stars over three decades |
we derive a bayesian framework for incorporating selection effects into population analyses. we allow for both measurement uncertainty in individual measurements and, crucially, for selection biases on the population of measurements, and show how to extract the parameters of the underlying distribution based on a set of observations sampled from this distribution. we illustrate the performance of this framework with an example from gravitational-wave astrophysics, demonstrating that the mass ratio distribution of merging compact-object binaries can be extracted from malmquist-biased observations with substantial measurement uncertainty. | extracting distribution parameters from multiple uncertain observations with selection biases |
alma cycle 2 observations of long-wavelength dust emission in 145 star-forming galaxies are used to probe the evolution of the star-forming interstellar medium (ism). we also develop a physical basis and empirical calibration (with 72 low-z and z ∼ 2 galaxies) for using the dust continuum as a quantitative probe of ism masses. the galaxies with the highest star formation rates (sfrs) at < z> = 2.2 and 4.4 have gas masses up to 100 times that of the milky way and gas mass fractions reaching 50%-80%, i.e., gas masses 1-4× their stellar masses. we find a single high-z star formation law: {sfr}=35 {m}{mol}0.89× {(1+z)}z=20.95× {({ssfr})}{ms}0.23 {m}⊙yr-1—an approximately linear dependence on the ism mass and an increased star formation efficiency per unit gas mass at higher redshift. galaxies above the main sequence (ms) have larger gas masses but are converting their ism into stars on a timescale only slightly shorter than those on the ms; thus, these “starbursts” are largely the result of having greatly increased gas masses rather than an increased efficiency of converting gas to stars. at z > 1, the entire population of star-forming galaxies has ∼2-5 times shorter gas depletion times than low-z galaxies. these shorter depletion times indicate a different mode of star formation in the early universe—most likely dynamically driven by compressive, high-dispersion gas motions—a natural consequence of the high gas accretion rates. | ism masses and the star formation law at z = 1 to 6: alma observations of dust continuum in 145 galaxies in the cosmos survey field |
the hubble constant (h0) measures the current expansion rate of the universe, and plays a fundamental role in cosmology. tremendous effort has been dedicated over the past decades to measure h0 (refs. 1-10). gravitational wave (gw) sources accompanied by electromagnetic (em) counterparts offer an independent standard siren measurement of h0 (refs. 11-13), as demonstrated following the discovery of the neutron star merger, gw170817 (refs. 14-16). this measurement does not assume a cosmological model and is independent of a cosmic distance ladder. the first joint analysis of the gw signal from gw170817 and its em localization led to a measurement of h0=7 4-8+16km s-1mpc-1 (median and symmetric 68% credible interval)13. in this analysis, the degeneracy in the gw signal between the source distance and the observing angle dominated the h0 measurement uncertainty. recently, tight constraints on the observing angle using high angular resolution imaging of the radio counterpart of gw170817 have been obtained17. here, we report an improved measurement h0=70 .3-5.0+5.3km s-1mpc-1 by using these new radio observations, combined with the previous gw and em data. we estimate that 15 more gw170817-like events, having radio images and light curve data, as compared with 50-100 gw events without such data18,19, will potentially resolve the tension between the planck and cepheid-supernova measurements. | a hubble constant measurement from superluminal motion of the jet in gw170817 |
ultraluminous x-ray sources (ulxs) in nearby galaxies shine brighter than any x-ray source in our galaxy. ulxs are usually modeled as stellar-mass black holes (bhs) accreting at very high rates or intermediate-mass bhs. we present observations showing that ngc 5907 ulx is instead an x-ray accreting neutron star (ns) with a spin period evolving from 1.43 seconds in 2003 to 1.13 seconds in 2014. it has an isotropic peak luminosity of ~1000 times the eddington limit for a ns at 17.1 megaparsec. standard accretion models fail to explain its luminosity, even assuming beamed emission, but a strong multipolar magnetic field can describe its properties. these findings suggest that other extreme ulxs (x-ray luminosity ≥ 1041 erg second-1) might harbor nss. | an accreting pulsar with extreme properties drives an ultraluminous x-ray source in ngc 5907 |
the new capabilities that jwst offers in the near- and mid-infrared (ir) are used to investigate in unprecedented detail the nature of optical/near-ir-faint, mid-ir-bright sources, with hst-dark galaxies among them. we gather jwst data from the ceers survey in the extended groth strip, jointly with hst data, and analyze spatially resolved optical-to-mid-ir spectral energy distributions to estimate photometric redshifts in two dimensions and stellar population properties on a pixel-by-pixel basis for red galaxies detected by nircam. we select 138 galaxies with f150w - f356w > 1.5 mag and f356w < 27.5 mag. the nature of these sources is threefold: (1) 71% are dusty star-forming galaxies (sfgs) at 2 < z < 6 with $9\lt \mathrm{log}{m}_{\star }/{m}_{\odot }\lt 11$ and a variety of specific sfrs (<1 to >100 gyr-1); (2) 18% are quiescent/dormant (i.e., subject to reignition/rejuvenation) galaxies (qgs) at 3 < z < 5, with $\mathrm{log}{m}_{\star }/{m}_{\odot }\sim 10$ and poststarburst mass-weighted ages (0.5-1.0 gyr); and (3) 11% are strong young starbursts with indications of high equivalent width emission lines (typically, [o iii]+hβ) at 6 < z < 7 (xelg-z6) and $\mathrm{log}{m}_{\star }/{m}_{\odot }\sim 9.5$ . the sample is dominated by disk-like galaxies with remarkable compactness for xelg-z6 (effective radii smaller than 0.4 kpc). large attenuations in sfgs, 2 < a(v) < 5 mag, are found within 1.5 times the effective radius, approximately 2 kpc, while qgs present a(v) ~ 0.2 mag. our sed-fitting technique reproduces the expected dust emission luminosities of ir-bright and submillimeter galaxies. this study implies high levels of star formation activity between z ~ 20 and z ~ 10, where virtually 100% of our galaxies had already formed 108 m ⊙, 60% had assembled 109 m ⊙, and 10% up to 1010 m ⊙ (in situ or ex situ). | ceers key paper. iv. a triality in the nature of hst-dark galaxies |
observational advances over the last decade have enabled high-resolution, interferometric studies of forming multiple systems, statistical surveys of multiplicity in star-forming regions, and new insights into disk evolution and planetary architectures in these systems. in this review, we compile the results of observational and theoretical studies of stellar multiplicity. we summarize the population statistics spanning system evolution from the protostellar phase through the main-sequence phase and evaluate the influence of the local environment. in short, most stars are born in multiple stellar systems, most main sequence stars are members of multiple systems, but most star systems are single. we describe current models for the origin of stellar multiplicity and review the landscape of numerical simulations and evaluate their consistency with observations. we review the properties of disks and discuss the impact of multiplicity on planet formation and system architectures. finally, we summarize open questions and discuss the technical requirements for future observational and theoretical progress. | the origin and evolution of multiple star systems |
we explore the evolution of stellar mass black hole binaries (bhbs) which are formed in the self-gravitating discs of active galactic nuclei (agn). hardening due to three-body scattering and gaseous drag are effective mechanisms that reduce the semimajor axis of a bhb to radii where gravitational waves take over, on time-scales shorter than the typical lifetime of the agn disc. taking observationally motivated assumptions for the rate of star formation in agn discs, we find a rate of disc-induced bhb mergers (r ∼ 3 yr^{-1} gpc^{-3}, but with large uncertainties) that is comparable with existing estimates of the field rate of bhb mergers, and the approximate bhb merger rate implied by the recent advanced ligo detection of gw150914. bhbs formed thorough this channel will frequently be associated with luminous agn, which are relatively rare within the sky error regions of future gravitational wave detector arrays. this channel could also possess a (potentially transient) electromagnetic counterpart due to super-eddington accretion on to the stellar mass black hole following the merger. | assisted inspirals of stellar mass black holes embedded in agn discs: solving the `final au problem' |
directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. using the gemini planet imager, we discovered a planet orbiting the ~20-million-year-old star 51 eridani at a projected separation of 13 astronomical units. near-infrared observations show a spectrum with strong methane and water-vapor absorption. modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the sun) of 1.6 to 4.0 × 10-6 and an effective temperature of 600 to 750 kelvin. for this age and luminosity, “hot-start” formation models indicate a mass twice that of jupiter. this planet also has a sufficiently low luminosity to be consistent with the “cold-start” core-accretion process that may have formed jupiter. | discovery and spectroscopy of the young jovian planet 51 eri b with the gemini planet imager |
we revisit the constraint on the maximum mass of cold spherical neutron stars coming from the observational results of gw170817. we develop a new framework for the analysis by employing both energy and angular momentum conservation laws as well as solid results of latest numerical-relativity simulations and of neutron stars in equilibrium. the new analysis shows that the maximum mass of cold spherical neutron stars can be only weakly constrained as mmax≲2.3 m⊙. our present result illustrates that the merger remnant neutron star at the onset of collapse to a black hole is not necessarily rapidly rotating and shows that we have to take into account the angular momentum conservation law to impose the constraint on the maximum mass of neutron stars. | constraint on the maximum mass of neutron stars using gw170817 event |
we present the localization and host galaxies of one repeating and two apparently nonrepeating fast radio bursts (frbs). frb 20180301a was detected and localized with the karl g. jansky very large array to a star-forming galaxy at z = 0.3304. frb20191228a and frb20200906a were detected and localized by the australian square kilometre array pathfinder to host galaxies at z = 0.2430 and z = 0.3688, respectively. we combine these with 13 other well-localized frbs in the literature, and analyze the host galaxy properties. we find no significant differences in the host properties of repeating and apparently nonrepeating frbs. frb hosts are moderately star forming, with masses slightly offset from the star-forming main sequence. star formation and low-ionization nuclear emission-line region emission are major sources of ionization in frb host galaxies, with the former dominant in repeating frb hosts. frb hosts do not track stellar mass and star formation as seen in field galaxies (more than 95% confidence). frbs are rare in massive red galaxies, suggesting that progenitor formation channels are not solely dominated by delayed channels which lag star formation by gigayears. the global properties of frb hosts are indistinguishable from core-collapse supernovae and short gamma-ray bursts hosts, and the spatial offset (from galaxy centers) of frbs is mostly inconsistent with that of the galactic neutron star population (95% confidence). the spatial offsets of frbs (normalized to the galaxy effective radius) also differ from those of globular clusters in late- and early-type galaxies with 95% confidence. | characterizing the fast radio burst host galaxy population and its connection to transients in the local and extragalactic universe |
dark matter detectors built primarily to probe elastic scattering of wimps on nuclei are also precise probes of light, weakly coupled, particles that may be absorbed by the detector material. in this paper, we derive constraints on the minimal model of dark matter comprised of long-lived vector states v (dark photons) in the 0.01- 100 kev mass range. the absence of an ionization signal in direct detection experiments such as xenon10 and xenon100 places a very strong constraint on the dark photon mixing angle, down to o (10-15), assuming that dark photons comprise the dominant fraction of dark matter. this sensitivity to dark photon dark matter exceeds the indirect bounds derived from stellar energy loss considerations over a significant fraction of the available mass range. we also revisit indirect constraints from v → 3 γ decay and show that limits from modifications to the cosmological ionization history are comparable to the updated limits from the diffuse γ-ray flux. | direct detection constraints on dark photon dark matter |
black hole binary systems with companion stars are typically found via their x-ray emission, generated by interaction and accretion. noninteracting binaries are expected to be plentiful in the galaxy but must be observed using other methods. we combine radial velocity and photometric variability data to show that the bright, rapidly rotating giant star 2mass j05215658+4359220 is in a binary system with a massive unseen companion. the system has an orbital period of ~83 days and near-zero eccentricity. the photometric variability period of the giant is consistent with the orbital period, indicating star spots and tidal synchronization. constraints on the giant’s mass and radius imply that the unseen companion is 3.3-0.7+2.8 solar masses, indicating that it is a noninteracting low-mass black hole or an unexpectedly massive neutron star. | a noninteracting low-mass black hole-giant star binary system |
the neutron star tidal deformability is a critical parameter which determines the premerger gravitational-wave signal in a neutron star merger. in this article, we show how neutron star tidal deformabilities behave in the presence of one or two sharp phase transition(s). we characterize how the tidal deformability changes when the properties of these phase transitions are modified in dense matter equations of state. sharp phase transitions lead to the smallest possible tidal deformabilities and also induce discontinuities in the relation between tidal deformability and gravitational mass. these results are qualitatively unmodified by a modest softening of the phase transition. finally, we test two universal relations involving the tidal deformability and show that their accuracy is limited by sharp phase transitions. | tidal deformability with sharp phase transitions in binary neutron stars |
the galactic archaeology with hermes (galah) survey is a large-scale stellar spectroscopic survey of the milky way, designed to deliver complementary chemical information to a large number of stars covered by the gaia mission. we present the galah second public data release (galah dr2) containing 342 682 stars. for these stars, the galah collaboration provides stellar parameters and abundances for up to 23 elements to the community. here we present the target selection, observation, data reduction, and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. for the stellar analysis, we have used a multistep approach. we use the physics-driven spectrum synthesis of spectroscopy made easy (sme) to derive stellar labels (teff, log g, [fe/h], [x/fe], vmic, vsin i, a_{k_s}) for a representative training set of stars. this information is then propagated to the whole sample with the data-driven method of the cannon. special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. departures from local thermodynamic equilibrium (lte) are considered for several key elements, including li, o, na, mg, al, si, and fe, using 1d marcs stellar atmosphere models. validation tests including repeat observations, gaia benchmark stars, open and globular clusters, and k2 asteroseismic targets lend confidence to our methods and results. combining the galah dr2 catalogue with the kinematic information from gaia will enable a wide range of galactic archaeology studies, with unprecedented detail, dimensionality, and scope. | the galah survey: second data release |
recent observations with the \textit{james webb} space telescope (jwst) have further refined the spectroscopic redshift of gn-z11, one of the most distant galaxies identified with the \textit{hubble} space telescope (hst) at $z=10.603$. the presence of extremely dense gas ($>10^{10}$ cm$^{-3}$), the detection of high-ionisation lines and of cii*1335 emission, as well as the presence of an ionisation cone, indicate that gn-z11 also hosts an active galactic nucleus (agn). further photometric and spectroscopic follow-up demonstrates that it lies in a large-scale, overdense structure with possible signatures of population iii (popiii) stars in its halo. surprisingly, ly$\alpha$ has also been detected despite the expected largely neutral inter-galactic medium at such a redshift. we exploit recent jwst/nirspec ifu observations to demonstrate that the ly$\alpha$ emission in gn-z11 is part of an extended halo with a minimum size of 0.8--3.2 kpc, depending on the definition used to derive the halo size. the surface brightness of the ly$\alpha$ halo around gn-z11 appears consistent with ly$\alpha$ halos observed around $z\sim6$ quasars. at the wavelength of ly$\alpha$ at $z\sim$10.6, we identify three other emission line candidates within the ifu field-of-view with no uv rest-frame counterpart visible in deep images from the jwst/nircam. if confirmed, this could be the first evidence that the local region of gn-z11 represents a candidate protocluster core, forming just 400 myr after the big bang. we give a first estimate of the dark matter halo mass of this structure ($m_h$=2.96$^{+0.44}_{-0.39} \times$10$^{10}$ m$_{\odot}$), consistent with a coma-like cluster progenitor. | gn-z11: the environment of an agn at $z=$10.603 |
the production of elements by rapid neutron capture (r-process) in neutron-star mergers is expected theoretically and is supported by multimessenger observations1-3 of gravitational-wave event gw170817: this production route is in principle sufficient to account for most of the r-process elements in the universe4. analysis of the kilonova that accompanied gw170817 identified5,6 delayed outflows from a remnant accretion disk formed around the newly born black hole7-10 as the dominant source of heavy r-process material from that event9,11. similar accretion disks are expected to form in collapsars (the supernova-triggering collapse of rapidly rotating massive stars), which have previously been speculated to produce r-process elements12,13. recent observations of stars rich in such elements in the dwarf galaxy reticulum ii14, as well as the galactic chemical enrichment of europium relative to iron over longer timescales15,16, are more consistent with rare supernovae acting at low stellar metallicities than with neutron-star mergers. here we report simulations that show that collapsar accretion disks yield sufficient r-process elements to explain observed abundances in the universe. although these supernovae are rarer than neutron-star mergers, the larger amount of material ejected per event compensates for the lower rate of occurrence. we calculate that collapsars may supply more than 80 per cent of the r-process content of the universe. | collapsars as a major source of r-process elements |
determining the sound speed csin compact stars is an important open question with numerous implications on the behavior of matter at large densities and hence on gravitational-wave emission from neutron stars. to this scope, we construct more than 107 equations of state (eoss) with continuous sound speed and build more than 108 nonrotating stellar models consistent not only with nuclear theory and perturbative qcd, but also with astronomical observations. in this way, we find that eoss with subconformal sound speeds, i.e., with ${c}_{s}^{2}\lt 1/3$ within the stars, are possible in principle but very unlikely in practice, being only 0.03% of our sample. hence, it is natural to expect that ${c}_{s}^{2}\gt 1/3$ somewhere in the stellar interior. using our large sample, we obtain estimates at 95% credibility of neutron-star radii for representative stars with 1.4 and 2.0 solar masses, ${r}_{1.4}={12.42}_{-0.99}^{+0.52}\,\mathrm{km}$ , ${r}_{2.0}={12.12}_{-1.23}^{+1.11}\,\mathrm{km}$ , and for the binary tidal deformability of the gw170817 event, ${\tilde{{\rm{\lambda }}}}_{1.186}={485}_{-211}^{+225}$ . interestingly, our lower bounds on the radii are in very good agreement with the prediction derived from very different arguments, namely, the threshold mass. finally, we provide simple analytic expressions to determine the minimum and maximum values of $\tilde{{\rm{\lambda }}}$ as a function of the chirp mass. | on the sound speed in neutron stars |
how turbulent energy is dissipated in weakly collisional space and astrophysical plasmas is a major open question. here, we present the application of a field-particle correlation technique to directly measure the transfer of energy between the turbulent electromagnetic field and electrons in the earth's magnetosheath, the region of solar wind downstream of the earth's bow shock. the measurement of the secular energy transfer from the parallel electric field as a function of electron velocity shows a signature consistent with landau damping. this signature is coherent over time, close to the predicted resonant velocity, similar to that seen in kinetic alfven turbulence simulations, and disappears under phase randomisation. this suggests that electron landau damping could play a significant role in turbulent plasma heating, and that the technique is a valuable tool for determining the particle energisation processes operating in space and astrophysical plasmas | evidence for electron landau damping in space plasma turbulence |
when two black holes merge in a dense star cluster, they form a new black hole with a well-defined mass and spin. if that "second-generation" black hole remains in the cluster, it will continue to participate in dynamical encounters, form binaries, and potentially merge again. using a grid of 96 dynamical models of dense star clusters and a cosmological model of cluster formation, we explore the production of binary black hole mergers where at least one component of the binary was forged in a previous merger. we create four hypothetical universes where every black hole born in the collapse of a massive star has a dimensionless kerr spin parameter, χbirth , of 0.0, 0.1, 0.2, or 0.5. we show that if all stellar-born black holes are nonspinning (χbirth=0.0 ), then more than 10% of merging binary black holes from clusters have components formed from previous mergers, accounting for more than 20% of the mergers from globular clusters detectable by ligo/virgo. furthermore, nearly 7% of detectable mergers would have a component with a mass ≳55 m⊙, placing it clearly in the mass "gap" region where black holes cannot form from isolated collapsing stars due to the pulsational-pair instability mechanism. on the other hand, if black holes are born spinning, then the contribution from these second-generation mergers decreases, making up as little as 1% of all detections from globular clusters when χbirth=0.5 . we make quantitative predictions for the detected masses, mass ratios, and spin properties of first- and second-generation mergers from dense star clusters, and show how these distributions are highly sensitive to the birth spins of black holes. | black holes: the next generation—repeated mergers in dense star clusters and their gravitational-wave properties |
the strong interaction among hadrons has been measured in the past by scattering experiments. although this technique has been extremely successful in providing information about the nucleon-nucleon and pion-nucleon interactions, when unstable hadrons are considered the experiments become more challenging. in the last few years, the analysis of correlations in the momentum space for pairs of stable and unstable hadrons measured in pp and p+pb collisions by the alice collaboration at the lhc has provided a new method to investigate the strong interaction among hadrons. in this article, we review the numerous results recently achieved for hyperon-nucleon, hyperon-hyperon, and kaon-nucleon pairs, which show that this new method opens the possibility of measuring the residual strong interaction of any hadron pair. | study of the strong interaction among hadrons with correlations at the lhc |
the solar wind is a magnetized plasma and as such exhibits collective plasma behavior associated with its characteristic spatial and temporal scales. the characteristic length scales include the size of the heliosphere, the collisional mean free paths of all species, their inertial lengths, their gyration radii, and their debye lengths. the characteristic timescales include the expansion time, the collision times, and the periods associated with gyration, waves, and oscillations. we review the past and present research into the multi-scale nature of the solar wind based on in-situ spacecraft measurements and plasma theory. we emphasize that couplings of processes across scales are important for the global dynamics and thermodynamics of the solar wind. we describe methods to measure in-situ properties of particles and fields. we then discuss the role of expansion effects, non-equilibrium distribution functions, collisions, waves, turbulence, and kinetic microinstabilities for the multi-scale plasma evolution. | the multi-scale nature of the solar wind |
the atacama large millimeter array (alma) large program to investigate [cii] at early times (alpine) targets the [cii] 158 μm line and the far-infrared continuum in 118 spectroscopically confirmed star-forming galaxies between z = 4.4 and z = 5.9. it represents the first large [cii] statistical sample built in this redshift range. we present details regarding the data processing and the construction of the catalogs. we detected 23 of our targets in the continuum. to derive accurate infrared luminosities and obscured star formation rates (sfrs), we measured the conversion factor from the alma 158 μm rest-frame dust continuum luminosity to the total infrared luminosity (lir) after constraining the dust spectral energy distribution by stacking a photometric sample similar to alpine in ancillary single-dish far-infrared data. we found that our continuum detections have a median lir of 4.4 × 1011 l⊙. we also detected 57 additional continuum sources in our alma pointings. they are at a lower redshift than the alpine targets, with a mean photometric redshift of 2.5 ± 0.2. we measured the 850 μm number counts between 0.35 and 3.5 mjy, thus improving the current interferometric constraints in this flux density range. we found a slope break in the number counts around 3 mjy with a shallower slope below this value. more than 40% of the cosmic infrared background is emitted by sources brighter than 0.35 mjy. finally, we detected the [cii] line in 75 of our targets. their median [cii] luminosity is 4.8 × 108 l⊙ and their median full width at half maximum is 252 km s-1. after measuring the mean obscured sfr in various [cii] luminosity bins by stacking alpine continuum data, we find a good agreement between our data and the local and predicted sfr-l[cii] relations. the catalogs are also 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/643/a2 the alpine products are publicly available at https://cesam.lam.fr/a2c2s/ | the alpine-alma [cii] survey: data processing, catalogs, and statistical source properties |
fast radio bursts (frbs) are highly dispersed, millisecond-duration radio bursts1-3. recent observations of a galactic frb4-8 suggest that at least some frbs originate from magnetars, but the origin of cosmological frbs is still not settled. here we report the detection of 1,863 bursts in 82 h over 54 days from the repeating source frb 20201124a (ref. 9). these observations show irregular short-time variation of the faraday rotation measure (rm), which scrutinizes the density-weighted line-of-sight magnetic field strength, of individual bursts during the first 36 days, followed by a constant rm. we detected circular polarization in more than half of the burst sample, including one burst reaching a high fractional circular polarization of 75%. oscillations in fractional linear and circular polarizations, as well as polarization angle as a function of wavelength, were detected. all of these features provide evidence for a complicated, dynamically evolving, magnetized immediate environment within about an astronomical unit (au; earth-sun distance) of the source. our optical observations of its milky-way-sized, metal-rich host galaxy10-12 show a barred spiral, with the frb source residing in a low-stellar-density interarm region at an intermediate galactocentric distance. this environment is inconsistent with a young magnetar engine formed during an extreme explosion of a massive star that resulted in a long gamma-ray burst or superluminous supernova. | a fast radio burst source at a complex magnetized site in a barred galaxy |
in a companion paper by koposov et al., rr lyrae from gaia data release 2 are used to demonstrate that stars in the orphan stream have velocity vectors significantly misaligned with the stream track, suggesting that it has received a large gravitational perturbation from a satellite of the milky way. we argue that such a mismatch cannot arise due to any realistic static milky way potential and then explore the perturbative effects of the large magellanic cloud (lmc). we find that the lmc can produce precisely, the observed motion-track mismatch and we therefore use the orphan stream to measure the mass of the cloud. we simultaneously fit the milky way and lmc potentials and infer that a total lmc mass of 1.38^{+0.27}_{-0.24} × 10^{11} {m_⊙ } is required to bend the orphan stream, showing for the first time that the lmc has a large and measurable effect on structures orbiting the milky way. this has far-reaching consequences for any technique which assumes that tracers are orbiting a static milky way. furthermore, we measure the milky way mass within 50 kpc to be 3.80^{+0.14}_{-0.11}× 10^{11} m_⊙. finally, we use these results to predict that, due to the reflex motion of the milky way in response to the lmc, the outskirts of the milky way's stellar halo should exhibit a bulk, upwards motion. | the total mass of the large magellanic cloud from its perturbation on the orphan stream |
this is an introduction to bayesian inference with a focus on hierarchical models and hyper-parameters. we write primarily for an audience of bayesian novices, but we hope to provide useful insights for seasoned veterans as well. examples are drawn from gravitational-wave astronomy, though we endeavour for the presentation to be understandable to a broader audience. we begin with a review of the fundamentals: likelihoods, priors, and posteriors. next, we discuss bayesian evidence, bayes factors, odds ratios, and model selection. from there, we describe how posteriors are estimated using samplers such as markov chain monte carlo algorithms and nested sampling. finally, we generalise the formalism to discuss hyper-parameters and hierarchical models. we include extensive appendices discussing the creation of credible intervals, gaussian noise, explicit marginalisation, posterior predictive distributions, and selection effects. | an introduction to bayesian inference in gravitational-wave astronomy: parameter estimation, model selection, and hierarchical models |
a large fraction of the protoplanetary disks observed with alma display multiple well-defined and nearly perfectly circular rings in the continuum, in many cases with substantial peak-to-valley contrast. the dsharp campaign shows that several of these rings are very narrow in radial extent. in this letter we test the hypothesis that these dust rings are caused by dust trapping in radial pressure bumps, and if confirmed, put constraints on the physics of the dust trapping mechanism. we model this process analytically in 1d, assuming axisymmetry. by comparing this model to the data, we find that all rings are consistent with dust trapping. based on a plausible model of the dust temperature we find that several rings are narrower than the pressure scale height, providing strong evidence for dust trapping. the rings have peak absorption optical depth in the range between 0.2 and 0.5. the dust masses stored in each of these rings is of the order of tens of earth masses, though much ambiguity remains due to the uncertainty of the dust opacities. the dust rings are dense enough to potentially trigger the streaming instability, but our analysis cannot give proof of this mechanism actually operating. our results show, however, that the combination of very low {α }turb}\ll 5× {10}-4 and very large grains {a}grain}\gg 0.1 {cm} can be excluded by the data for all the rings studied in this letter. | the disk substructures at high angular resolution project (dsharp). vi. dust trapping in thin-ringed protoplanetary disks |
we report deep chandra x-ray observatory (cxo), hubble space telescope (hst), and karl j. jansky very large array (vla) observations of the binary neutron star event gw170817 at t < 160 days after merger. these observations show that gw170817 has been steadily brightening with time and might have now reached its peak, and constrain the emission process as non-thermal synchrotron emission where the cooling frequency νcis above the x-ray band and the synchrotron frequency νmis below the radio band. the very simple power-law spectrum extending for eight orders of magnitude in frequency enables the most precise measurement of the index p of the distribution of non-thermal relativistic electrons n(γ )\propto {γ }-p accelerated by a shock launched by a neutron star (ns)-ns merger to date. we find p = 2.17 ± 0.01, which indicates that radiation from ejecta with γ ∼ 3-10 dominates the observed emission. while constraining the nature of the emission process, these observations do not constrain the nature of the relativistic ejecta. we employ simulations of explosive outflows launched in ns ejecta clouds to show that the spectral and temporal evolution of the non-thermal emission from gw170817 is consistent with both emission from radially stratified quasi-spherical ejecta traveling at mildly relativistic speeds, and emission from off-axis collimated ejecta characterized by a narrow cone of ultra-relativistic material with slower wings extending to larger angles. in the latter scenario, gw170817 harbored a normal short gamma-ray burst (sgrb) directed away from our line of sight. observations at t ≤ 200 days are unlikely to settle the debate, as in both scenarios the observed emission is effectively dominated by radiation from mildly relativistic material. | the binary neutron star event ligo/virgo gw170817 160 days after merger: synchrotron emission across the electromagnetic spectrum |
we present a statistical study of 180 dust continuum sources identified in 33 massive cluster fields by the alma lensing cluster survey (alcs) over a total of 133 arcmin$^{2}$ area, homogeneously observed at 1.2 mm. alcs enables us to detect extremely faint mm sources by lensing magnification, including near-infrared (nir) dark objects showing no counterparts in existing {\it hubble space telescope} and {\it spitzer} images. the dust continuum sources belong to a blind sample ($n=141$) with s/n $\gtrsim$ 5.0 (a purity of $>$ 0.99) or a secondary sample ($n=39$) with s/n= $4.0-5.0$ screened by priors. with the blind sample, we securely derive 1.2-mm number counts down to $\sim7$ $\mu$jy, and find that the total integrated 1.2mm flux is 20.7$^{+8.5}_{-6.5}$ jy deg$^{-2}$, resolving $\simeq$ 80 % of the cosmic infrared background light. the resolved fraction varies by a factor of $0.6-1.1$ due to the completeness correction depending on the spatial size of the mm emission. we also derive infrared (ir) luminosity functions (lfs) at $z=0.6-7.5$ with the $1/v_{\rm max}$ method, finding the redshift evolution of ir lfs characterized by positive luminosity and negative density evolution. the total (=uv+ir) cosmic star-formation rate density (sfrd) at $z>4$ is estimated to be $161^{+25}_{-21}$ % of the established measurements, which were almost exclusively based on optical$-$nir surveys. although our general understanding of the cosmic sfrd is unlikely to change beyond a factor of 2, these results add to the weight of evidence for an additional ($\approx 60$ %) sfrd component contributed by the faint-mm population, including nir dark objects. | alma lensing cluster survey: deep 1.2 mm number counts and infrared luminosity functions at $z\\simeq1-8$ |
it remains a major challenge to derive a theory of cloud-scale (≲100 pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (gmc) lifecycle. we address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the gmc lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the phangs-alma survey. we measure the spatially resolved (∼100 pc) co-to-h α flux ratio and find a universal de-correlation between molecular gas and young stars on gmc scales, allowing us to quantify the underlying evolutionary timeline. gmc lifetimes are short, typically 10-30 myr, and exhibit environmental variation, between and within galaxies. at kpc-scale molecular gas surface densities σ _h_2≥8 m_⊙ pc^{-2}, the gmc lifetime correlates with time-scales for galactic dynamical processes, whereas at σ _h_2≤8 m_⊙ pc^{-2} gmcs decouple from galactic dynamics and live for an internal dynamical time-scale. after a long inert phase without massive star formation traced by h α (75-90 per cent of the cloud lifetime), gmcs disperse within just 1-5 myr once massive stars emerge. the dispersal is most likely due to early stellar feedback, causing gmcs to achieve integrated star formation efficiencies of 4-10 per cent. these results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. gmcs and h ii regions are the fundamental units undergoing these lifecycles, with mean separations of 100-300 pc in star-forming discs. future work should characterize the multiscale physics and mass flows driving these lifecycles. | the lifecycle of molecular clouds in nearby star-forming disc galaxies |
we present atacama large millimeter/sub-millimeter array (alma) band 6 observations of a complete sample of protoplanetary disks in the young (∼1-3 myr) lupus star-forming region, covering the 1.33 mm continuum and the 12co, 13co, and c18o j = 2-1 lines. the spatial resolution is ∼0.″25 with a medium 3σ continuum sensitivity of 0.30 mjy, corresponding to m dust ∼ 0.2 m ⊕. we apply keplerian masking to enhance the signal-to-noise ratios of our 12co zero-moment maps, enabling measurements of gas disk radii for 22 lupus disks; we find that gas disks are universally larger than millimeter dust disks by a factor of two on average, likely due to a combination of the optically thick gas emission and the growth and inward drift of the dust. using the gas disk radii, we calculate the dimensionless viscosity parameter, α visc, finding a broad distribution and no correlations with other disk or stellar parameters, suggesting that viscous processes have not yet established quasi-steady states in lupus disks. by combining our 1.33 mm continuum fluxes with our previous 890 μm continuum observations, we also calculate the millimeter spectral index, α mm, for 70 lupus disks; we find an anticorrelation between α mm and millimeter flux for low-mass disks (m dust ≲ 5), followed by a flattening as disks approach α mm ≈ 2, which could indicate faster grain growth in higher-mass disks, but may also reflect their larger optically thick components. in sum, this work demonstrates the continuous stream of new insights into disk evolution and planet formation that can be gleaned from unbiased alma disk surveys. | alma survey of lupus protoplanetary disks. ii. gas disk radii |
we present a detailed stellar population analysis of 11 bright (h < 26.6) galaxies at z = 9-11 (three spectroscopically confirmed) to constrain the chemical enrichment and growth of stellar mass of early galaxies. we use the flexible bayesian spectral energy distribution (sed) fitting code prospector with a range of star formation histories (sfhs), a flexible dust attenuation law, and a self-consistent model of emission lines. this approach allows us to assess how different priors affect our results and how well we can break degeneracies between dust attenuation, stellar ages, metallicity, and emission lines using data that probe only the rest-frame ultraviolet (uv) to optical wavelengths. we measure a median observed uv spectral slope $\beta =-{1.87}_{-0.43}^{+0.35}$ for relatively massive star-forming galaxies ( $9\lt \mathrm{log}({m}_{\star }/{m}_{\odot })\lt 10$ ), consistent with no change from z = 4 to z = 9-10 at these stellar masses, implying rapid enrichment. our sed-fitting results are consistent with a star-forming main sequence with sublinear slope (0.7 ± 0.2) and specific star formation rates of 3-10 gyr-1. however, the stellar ages and sfhs are less well constrained. using different sfh priors, we cannot distinguish between median mass-weighted ages of ~ 50-150 myr, which corresponds to 50% formation redshifts of z 50 ~ 10-12 at z ~ 9 and is of the order of the dynamical timescales of these systems. importantly, models with different sfh priors are able to fit the data equally well. we conclude that the current observational data cannot tightly constrain the mass-buildup timescales of these z = 9-11 galaxies, with our results consistent with sfhs implying both a shallow and steep increase in the cosmic sfr density with time at z > 10. | on the stellar populations of galaxies at z = 9-11: the growth of metals and stellar mass at early times |
in hierarchical models of structure formation, the first galaxies form in low-mass dark matter potential wells, probing the behavior of dark matter on kiloparsec scales. even though these objects are below the detection threshold of current telescopes, future missions will open an observational window into this emergent world. in this letter, we investigate how the first galaxies are assembled in a "fuzzy" dark matter (fdm) cosmology where dark matter is an ultralight ∼10-22 ev boson and the primordial stars are expected to form along dense dark matter filaments. using a first-of-its-kind cosmological hydrodynamical simulation, we explore the interplay between baryonic physics and unique wavelike features inherent to fdm. in our simulation, the dark matter filaments show coherent interference patterns on the boson de broglie scale and develop cylindrical solitonlike cores, which are unstable under gravity and collapse into kiloparsec-scale spherical solitons. features of the dark matter distribution are largely unaffected by the baryonic feedback. on the contrary, the distributions of gas and stars, which do form along the entire filament, exhibit central cores imprinted by dark matter—a smoking gun signature of fdm. | first star-forming structures in fuzzy cosmic filaments |
a new upper limit on the 21 cm signal power spectrum at a redshift of z ≈ 9.1 is presented, based on 141 h of data obtained with the low-frequency array (lofar). the analysis includes significant improvements in spectrally smooth gain-calibration, gaussian process regression (gpr) foreground mitigation and optimally weighted power spectrum inference. previously seen `excess power' due to spectral structure in the gain solutions has markedly reduced but some excess power still remains with a spectral correlation distinct from thermal noise. this excess has a spectral coherence scale of 0.25-0.45 mhz and is partially correlated between nights, especially in the foreground wedge region. the correlation is stronger between nights covering similar local sidereal times. a best 2-σ upper limit of δ ^2_{21} < (73)^2 mk^2 at k = 0.075 h cmpc^{-1} is found, an improvement by a factor ≈8 in power compared to the previously reported upper limit. the remaining excess power could be due to residual foreground emission from sources or diffuse emission far away from the phase centre, polarization leakage, chromatic calibration errors, ionosphere, or low-level radiofrequency interference. we discuss future improvements to the signal processing chain that can further reduce or even eliminate these causes of excess power. | improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from lofar |
icy grain mantles are the main reservoir of the volatile elements that link chemical processes in dark, interstellar clouds with the formation of planets and the composition of their atmospheres. the initial ice composition is set in the cold, dense parts of molecular clouds, before the onset of star formation. with the exquisite sensitivity of the james webb space telescope, this critical stage of ice evolution is now accessible for detailed study. here we show initial results of the early release science programme ice age that reveal the rich composition of these dense cloud ices. weak ice features, including 13co2, ocn−, 13co, ocs and complex organic molecule functional groups, are now detected along two pre-stellar lines of sight. the 12co2 ice profile indicates modest growth of the icy grains. column densities of the major and minor ice species indicate that ices contribute between 2% and 19% of the bulk budgets of the key c, o, n and s elements. our results suggest that the formation of simple and complex molecules could begin early in a water-ice-rich environment. | an ice age jwst inventory of dense molecular cloud ices |
a new line list for h_2^{ 16}o is presented. this line list, which is called pokazatel, includes transitions between rotational-vibrational energy levels up to 41 000 cm-1 and is the most complete to date. the potential energy surface (pes) used for producing the line list was obtained by fitting a high-quality ab initio pes to experimental energy levels with energies of 41 000 cm-1 and for rotational excitations up to j = 5. the final line list comprises all energy levels up to 41 000 cm-1 and rotational angular momentum j up to 72. an accurate ab initio dipole moment surface was used for the calculation of line intensities and reproduces high-precision experimental intensity data with an accuracy close to 1 per cent. the final line list uses empirical energy levels, whenever they are available, to ensure that line positions are reproduced as accurately as possible. the pokazatel line list contains over 5 billion transitions and is available from the exomol website (www.exomol.com) and the cds data base. | exomol molecular line lists xxx: a complete high-accuracy line list for water |
broadband photometry of galaxies measures an unresolved mix of complex stellar populations, gas, and dust. interpreting these data is a challenge for models: many studies have shown that properties derived from modeling galaxy photometry are uncertain by a factor of two or more, and yet answering key questions in the field now requires higher accuracy than this. here, we present a new model framework specifically designed for these complexities. our model, prospector- α, includes dust attenuation and re-radiation, a flexible attenuation curve, nebular emission, stellar metallicity, and a six-component nonparametric star formation history. the flexibility and range of the parameter space, coupled with monte carlo markov chain sampling within the prospector inference framework, is designed to provide unbiased parameters and realistic error bars. we assess the accuracy of the model with aperture-matched optical spectroscopy, which was excluded from the fits. we compare spectral features predicted solely from fits to the broadband photometry to the observed spectral features. our model predicts hα luminosities with a scatter of ∼0.18 dex and an offset of ∼0.1 dex across a wide range of morphological types and stellar masses. this agreement is remarkable, as the hα luminosity is dependent on accurate star formation rates, dust attenuation, and stellar metallicities. the model also accurately predicts dust-sensitive balmer decrements, spectroscopic stellar metallicities, polycyclic aromatic hydrocarbon mass fractions, and the age- and metallicity-sensitive features dn4000 and hδ. although the model passes all these tests, we caution that we have not yet assessed its performance at higher redshift or the accuracy of recovered stellar masses. | deriving physical properties from broadband photometry with prospector: description of the model and a demonstration of its accuracy using 129 galaxies in the local universe |
the first gravitational wave detections of mergers between black holes and neutron stars represent a remarkable new regime of high-energy transient astrophysics. the signals observed with ligo-virgo detectors come from mergers of extreme physical objects which are the end products of stellar evolution in close binary systems. to better understand their origin and merger rates, we have performed binary population syntheses at different metallicities using the new grid-based binary population synthesis code combine. starting from newborn pairs of stars, we follow their evolution including mass-loss, mass transfer and accretion, common envelopes, and supernova explosions. we apply the binding energies of common envelopes based on dense grids of detailed stellar structure models, make use of improved investigations of the subsequent case bb roche lobe overflow and scale supernova kicks according to the stripping of the exploding stars. we demonstrate that all the double black hole mergers, gw150914, lvt151012, gw151226, gw170104, gw170608, and gw170814, as well as the double neutron star merger gw170817, are accounted for in our models in the appropriate metallicity regime. our binary interaction parameters are calibrated to match the accurately determined properties of galactic double neutron star systems, and we discuss their masses and types of supernova origin. using our default values for the input physics parameters, we find a double neutron star merger rate of {3.0} myr^{-1} for milky-way equivalent galaxies. our upper limit to the merger-rate density of double neutron stars is r∼eq {400} yr^{-1} gpc^{-3} in the local universe (z = 0). | progenitors of gravitational wave mergers: binary evolution with the stellar grid-based code combine |
observations of galaxy isophotes, long-slit kinematics, and high-resolution photometry suggested a possible dichotomy between two distinct classes of elliptical galaxies. but these methods are expensive for large galaxy samples. instead, integral field spectroscopy can efficiently recognize the shape, dynamics, and stellar population of complete samples of early-type galaxies (etgs). these studies showed that the two main classes, the fast and slow rotators, can be separated using stellar kinematics. i show that there is a dichotomy in the dynamics of the two classes. the slow rotators are weakly triaxial and dominate above [formula: see text]. below mcrit, the structure of fast rotators parallels that of spiral galaxies. there is a smooth sequence along which the age, the metal content, the enhancement in α-elements, and the weight of the stellar initial mass function all increase with the central mass density slope, or bulge mass fraction, while the molecular gas fraction correspondingly decreases. the properties of etgs on galaxy scaling relations, in particular the [formula: see text] diagram, and their dependence on environment, indicate two main independent channels for galaxy evolution. fast-rotator etgs start as star-forming disks and evolve through a channel dominated by gas accretion, bulge growth, and quenching, whereas slow rotators assemble near the centers of massive halos via intense star formation at high redshift and remain as such for the rest of their evolution via a channel dominated by gas poor mergers. this is consistent with independent studies of the galaxies redshift evolution. | structure and kinematics of early-type galaxies from integral field spectroscopy |
we present observations and detailed characterizations of five new host galaxies of fast radio bursts (frbs) discovered with the australian square kilometre array pathfinder (askap) and localized to ≲1″. combining these galaxies with frb hosts from the literature, we introduce criteria based on the probability of chance coincidence to define a subsample of 10 highly confident associations (at z = 0.03-0.52), 3 of which correspond to known repeating frbs. overall, the frb-host galaxies exhibit a broad, continuous range of color (mu - mr = 0.9-2.0), stellar mass (m⋆ = 108 - 6 × 1010 m⊙), and star formation rate (sfr = 0.05-10 m⊙ yr-1) spanning the full parameter space occupied by z < 0.5 galaxies. however, they do not track the color-magnitude, sfr-m⋆, nor bpt diagrams of field galaxies surveyed at similar redshifts. there is an excess of "green valley" galaxies and an excess of emission-line ratios indicative of a harder radiation field than that generated by star formation alone. from the observed stellar mass distribution, we rule out the hypothesis that frbs strictly track stellar mass in galaxies (>99% c.l.). we measure a median offset of 3.3 kpc from the frb to the estimated center of the host galaxies and compare the host-burst offset distribution and other properties with the distributions of long- and short-duration gamma-ray bursts (lgrbs and sgrbs), core-collapse supernovae (cc-sne), and sne ia. this analysis rules out galaxies hosting lgrbs (faint, star-forming galaxies) as common hosts for frbs (>95% c.l.). other transient channels (sgrbs, cc-, and sne ia) have host-galaxy properties and offsets consistent with the frb distributions. all of the data and derived quantities are made publicly available on a dedicated website and repository. | host galaxy properties and offset distributions of fast radio bursts: implications for their progenitors |
photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability1. however, no unambiguous photochemical products have been detected in exoplanet atmospheres so far. recent observations from the jwst transiting exoplanet community early release science program2,3 found a spectral absorption feature at 4.05 μm arising from sulfur dioxide (so2) in the atmosphere of wasp-39b. wasp-39b is a 1.27-jupiter-radii, saturn-mass (0.28 mj) gas giant exoplanet orbiting a sun-like star with an equilibrium temperature of around 1,100 k (ref. 4). the most plausible way of generating so2 in such an atmosphere is through photochemical processes5,6. here we show that the so2 distribution computed by a suite of photochemical models robustly explains the 4.05-μm spectral feature identified by jwst transmission observations7 with nirspec prism (2.7σ)8 and g395h (4.5σ)9. so2 is produced by successive oxidation of sulfur radicals freed when hydrogen sulfide (h2s) is destroyed. the sensitivity of the so2 feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with wasp-39b exhibiting an inferred metallicity of about 10× solar. we further point out that so2 also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations. | photochemically produced so2 in the atmosphere of wasp-39b |
long-duration γ-ray bursts (grbs) are the most luminous sources of electromagnetic radiation known in the universe. they arise from outflows of plasma with velocities near the speed of light that are ejected by newly formed neutron stars or black holes (of stellar mass) at cosmological distances1,2. prompt flashes of megaelectronvolt-energy γ-rays are followed by a longer-lasting afterglow emission in a wide range of energies (from radio waves to gigaelectronvolt γ-rays), which originates from synchrotron radiation generated by energetic electrons in the accompanying shock waves3,4. although emission of γ-rays at even higher (teraelectronvolt) energies by other radiation mechanisms has been theoretically predicted5-8, it has not been previously detected7,8. here we report observations of teraelectronvolt emission from the γ-ray burst grb 190114c. γ-rays were observed in the energy range 0.2-1 teraelectronvolt from about one minute after the burst (at more than 50 standard deviations in the first 20 minutes), revealing a distinct emission component of the afterglow with power comparable to that of the synchrotron component. the observed similarity in the radiated power and temporal behaviour of the teraelectronvolt and x-ray bands points to processes such as inverse compton upscattering as the mechanism of the teraelectronvolt emission9-11. by contrast, processes such as synchrotron emission by ultrahigh-energy protons10,12,13 are not favoured because of their low radiative efficiency. these results are anticipated to be a step towards a deeper understanding of the physics of grbs and relativistic shock waves. | teraelectronvolt emission from the γ-ray burst grb 190114c |
present-day galaxies are surrounded by cool and enriched halo gas extending for hundreds of kiloparsecs. this halo gas is thought to be the dominant reservoir of material available to fuel future star formation, but direct constraints on its mass and physical properties have been difficult to obtain. we report the detection of a fast radio burst (frb 181112), localized with arcsecond precision, that passes through the halo of a foreground galaxy. analysis of the burst shows that the halo gas has low net magnetization and turbulence. our results imply predominantly diffuse gas in massive galactic halos, even those hosting active supermassive black holes, contrary to some previous results. | the low density and magnetization of a massive galaxy halo exposed by a fast radio burst |
ultraviolet light from early galaxies is thought to have ionized gas in the intergalactic medium. however, there are few observational constraints on this epoch because of the faintness of those galaxies and the redshift of their optical light into the infrared. we report the observation, in jwst imaging, of a distant galaxy that is magnified by gravitational lensing. jwst spectroscopy of the galaxy, at rest-frame optical wavelengths, detects strong nebular emission lines that are attributable to oxygen and hydrogen. the measured redshift is z = 9.51 ± 0.01, corresponding to 510 million years after the big bang. the galaxy has a radius of 16.2−7.2+4.6 parsecs, which is substantially more compact than galaxies with equivalent luminosity at z ~ 6 to 8, leading to a high star formation rate surface density. | a magnified compact galaxy at redshift 9.51 with strong nebular emission lines |
using a large sample of bright nearby stars with accurate gaia data release 2 astrometry and auxiliary spectroscopy we map out the properties of the principle galactic components such as the 'thin' and 'thick' discs and the halo. we confirm previous claims that in the solar neighbourhood, there exists a large population of metal-rich ([fe/h] > -0.7) stars on highly eccentric orbits. by studying the evolution of elemental abundances, kinematics, and stellar ages in the plane of azimuthal velocity vϕ and metallicity [fe/h], we demonstrate that this metal-rich halo-like component, which we dub the splash, is linked to the α-rich (or 'thick') disc. splash stars have little to no angular momentum and many are on retrograde orbits. they are predominantly old, but not as old as the stars deposited into the milky way (mw) in the last major merger. we argue, in agreement with several recent studies, that the splash stars may have been born in the mw's protodisc prior to the massive ancient accretion event which drastically altered their orbits. we cannot, however, rule out other (alternative) formation channels. taking advantage of the causal connection between the merger and the splash, we put constraints of the epoch of the last massive accretion event to have finished 9.5 gyr ago. the link between the local metal-rich and metal-poor retrograde stars is confirmed using a large suite of cutting-edge numerical simulations of the mw's formation. | the biggest splash |
we present an interstellar medium and stellar population analysis of three spectroscopically confirmed z > 7 galaxies in the early release observations jwst/nircam and jwst/nirspec data of the smacs j0723.3-7327 cluster. we use the bayesian spectral energy distribution-fitting code prospector with a flexible star formation history (sfh), a variable dust attenuation law, and a self-consistent model of nebular emission (continuum and emission lines). importantly, we self-consistently fit both the emission line fluxes from jwst/nirspec and the broad-band photometry from jwst/nircam, taking into account slit-loss effects. we find that these three z=7.6-8.5 galaxies (m⋆ ≈ 108 m⊙) are young with rising sfhs and mass-weighted ages of 3-4 myr, though we find indications for underlying older stellar populations. the inferred gas-phase metallicities broadly agree with the direct metallicity estimates from the auroral lines. the galaxy with the lowest gas-phase metallicity (zgas= 0.06 z⊙) has a steeply rising sfh, is very compact (<0.2 kpc), and has a high star formation rate surface density (σsfr ≈ 22 m⊙ yr-1 kpc-2), consistent with rapid gas accretion. the two other objects with higher gas-phase metallicities show more complex multicomponent morphologies on kpc scales, indicating that their recent increase in star formation rate is driven by mergers or internal, gravitational instabilities. we discuss effects of assuming different sfh priors or only fitting the photometric data. our analysis highlights the strength and importance of combining jwst imaging and spectroscopy for fully assessing the nature of galaxies at the earliest epochs. | jwst nircam + nirspec: interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs |
thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky earth-like planets to large gas giants grazing the surface of their host star. however, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. we have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet's birth, and evolution. ariel was conceived to observe a large number ( 1000) of transiting planets for statistical understanding, including gas giants, neptunes, super-earths and earth-size planets around a range of host star types using transit spectroscopy in the 1.25-7.8 μm spectral range and multiple narrow-band photometry in the optical. ariel will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-z materials compared to their colder solar system siblings. said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. observations of these warm/hot exoplanets, and in particular of their elemental composition (especially c, o, n, s, si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ariel will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ariel is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10-100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. these types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. the wavelength range proposed covers all the expected major atmospheric gases from e.g. h2o, co2, ch4 nh3, hcn, h2s through to the more exotic metallic compounds, such as tio, vo, and condensed species. simulations of ariel performance in conducting exoplanet surveys have been performed - using conservative estimates of mission performance and a full model of all significant noise sources in the measurement - using a list of potential ariel targets that incorporates the latest available exoplanet statistics. the conclusion at the end of the phase a study, is that ariel - in line with the stated mission objectives - will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives. | a chemical survey of exoplanets with ariel |
we investigate irregularity factors for a self-gravitating spherical star evolving in the presence of an imperfect fluid. we explore the gravitational field equations and the dynamical equations with the systematic construction in f (r ,t ) gravity, where t is the trace of the energy-momentum tensor. furthermore, we analyze two well-known differential equations (which occupy principal importance in the exploration of causes of energy density inhomogeneities) with the help of the weyl tensor and the conservation laws. the irregularity factors for a spherical star are examined for particular cases of dust and isotropic and anisotropic fluids in dissipative and nondissipative regimes in the framework of f (r ,t ) gravity. it is found that, as the complexity of the matter with the anisotropic stresses increases, the inhomogeneity factor corresponds more closely to one of the structure scalars. | causes of irregular energy density in f (r ,t ) gravity |
itsg-grace2018 is a new series of grace-only gravity field solutions based on reprocessed grace observation data (l1b rl03) and the latest atmosphere and ocean dealiasing product (aod1b rl06). it includes unconstrained monthly and constrained daily solutions, as well as a high-resolution static gravity field. compared to the previous itsg release, we implemented a number of improvements within the processing chain and use updated background models. in an effort to better model all known error sources, we propagate synthetic orientation uncertainties of the star camera assembly to the antenna offset correction for intersatellite ranging observations. this enables the disentanglement of the stationary noise of the k-band system and the nonstationary noise of the antenna offset correction. we further incorporated uncertainties of the atmosphere and ocean dealiasing product to reduce temporal aliasing effects. to mitigate errors in the applied ocean tide model, we used constrained grace estimates of selected tidal constituents as an additional background model. variability over quiet ocean areas suggests a 27% to 46% lower noise level compared to the current spherical harmonic solutions of the official processing centers (300 km gaussian filter applied). to ensure that the low noise floor is not accompanied by signal loss, we examined drainage basin averages, which showed consistent amplitudes with the official grace time series. these evaluations lead to the conclusion that itsg-grace2018 is a state-of-the-art grace time series which exhibits an excellent signal-to-noise ratio. | itsg-grace2018: overview and evaluation of a new grace-only gravity field time series |
in nuclear matter in neutron stars the flavor content (e.g., proton fraction) is subject to weak interactions, establishing flavor ($\beta$-)equilibrium. during the merger of two neutron stars there can be deviations from this equilibrium. by incorporating urca processes into general-relativistic hydrodynamics simulations, we study the resulting out-of-equilibrium dynamics during the collision. we provide the first direct evidence that microphysical transport effects at late times reach a hydrodynamic regime with a nonzero bulk viscosity, making neutron star collisions intrinsically viscous. finally, we identify signatures of this process in the post-merger gravitational wave emission. | emergence of microphysical viscosity in binary neutron star post-merger dynamics |
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