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early data from the james webb space telescope (jwst) have revealed a bevy of high-redshift galaxy candidates with unexpectedly high stellar masses. an immediate concern is the consistency of these candidates with galaxy formation in the standard λcdm cosmological model, wherein the stellar mass (m⋆) of a galaxy is limited by the available baryonic reservoir of its host dark matter halo. the mass function of dark matter haloes therefore imposes an absolute upper limit on the number density n (>m⋆, z) and stellar mass density ρ⋆ (>m⋆, z) of galaxies more massive than m⋆ at any epoch z. here i show that the most massive galaxy candidates in jwst observations at z ≈ 7-10 lie at the very edge of these limits, indicating an important unresolved issue with the properties of galaxies derived from the observations, how galaxies form at early times in λcdm or within this standard cosmology itself. | stress testing λcdm with high-redshift galaxy candidates |
the correlation of the tidal polarizabilities λ1-λ2 for gw170817 is predicted by combining dense-matter equations of state (eoss) that satisfy nuclear physics constraints with the chirp mass and mass asymmetry for this event. our models are constrained by calculations of the neutron-matter eos using chiral effective field theory hamiltonians with reliable error estimates up to once or twice the nuclear saturation density. in the latter case, we find that gw170817 does not improve our understanding of the eos. we contrast two distinct extrapolations to higher density: a minimal model (mm) which assumes that the eos is a smooth function of density described by a taylor expansion and a more general model parametrized by the speed of sound that admits phase transitions. this allows us to identify regions in the λ1-λ2 plots that could favor the existence of new phases of matter in neutron stars. we predict the combined tidal polarizability of the two neutron stars in gw170817 to be 80 ≤λ ∼≤580 (280 ≤λ ∼≤480 for the mm), which is smaller than the range suggested by the ligo-virgo data analysis. our analysis also shows that gw170817 requires a ns with m =1.4 m⊙ to have a radius 9.0 km<r1.4<13.6 km (11.3 km<r1.4<13.6 km for the mm). | critical examination of constraints on the equation of state of dense matter obtained from gw170817 |
merging neutron stars offer an excellent laboratory for simultaneously studying strong-field gravity and matter in extreme environments. we establish the physical association of an electromagnetic counterpart (em170817) with gravitational waves (gw170817) detected from merging neutron stars. by synthesizing a panchromatic data set, we demonstrate that merging neutron stars are a long-sought production site forging heavy elements by r-process nucleosynthesis. the weak gamma rays seen in em170817 are dissimilar to classical short gamma-ray bursts with ultrarelativistic jets. instead, we suggest that breakout of a wide-angle, mildly relativistic cocoon engulfing the jet explains the low-luminosity gamma rays, the high-luminosity ultraviolet-optical-infrared, and the delayed radio and x-ray emission. we posit that all neutron star mergers may lead to a wide-angle cocoon breakout, sometimes accompanied by a successful jet and sometimes by a choked jet. | illuminating gravitational waves: a concordant picture of photons from a neutron star merger |
the ligo and virgo collaborations have recently announced the detection of gravitational waves from a neutron star-neutron star merger (gw170817) and the simultaneous measurement of an optical counterpart (the γ -ray burst grb 170817a). the close arrival time of the gravitational and electromagnetic waves limits the difference in speed of photons and gravitons to be less than about 1 part in 1 015. this has three important implications for cosmological scalar-tensor gravity theories that are often touted as dark energy candidates and alternatives to the λ cold dark matter model. first, for the most general scalar-tensor theories—beyond horndeski models—three of the five parameters appearing in the effective theory of dark energy can now be severely constrained on astrophysical scales; we present the results of combining the new gravity wave results with galaxy cluster observations. second, the combination with the lack of strong equivalence principle violations exhibited by the supermassive black hole in m87 constrains the quartic galileon model to be cosmologically irrelevant. finally, we derive a new bound on the disformal coupling to photons that implies that such couplings are irrelevant for the cosmic evolution of the field. | implications of the neutron star merger gw170817 for cosmological scalar-tensor theories |
using antiferromagnets as active elements in spintronics requires the ability to manipulate and read-out the néel vector orientation. here we demonstrate for mn2au, a good conductor with a high ordering temperature suitable for applications, reproducible switching using current pulse generated bulk spin-orbit torques and read-out by magnetoresistance measurements. reversible and consistent changes of the longitudinal resistance and planar hall voltage of star-patterned epitaxial mn2au(001) thin films were generated by pulse current densities of ≃107 a/cm2. the symmetry of the torques agrees with theoretical predictions and a large read-out magnetoresistance effect of more than ≃6% is reproduced by ab initio transport calculations. | writing and reading antiferromagnetic mn2au by néel spin-orbit torques and large anisotropic magnetoresistance |
note to the readers: following the publication of the corrigendum, the article was corrected on 15 may 2020. context.aims: the goal of this paper is to demonstrate the outstanding quality of the second data release of the gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the milky way. we focus here on determining the proper motions of 75 galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the large and small magellanic clouds.methods: using data extracted from the gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. we demonstrate that the errors, statistical and systematic, are relatively well understood. we integrated the orbits of these objects in three different galactic potentials, and characterised their properties. we present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community.results: our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the milky way are all on high-inclination orbits, but that they do not share a single plane of motion; (iv) derive a lower limit for the mass of the milky way of 9.1-2.6+6.2 × 1011 m⊙ based on the assumption that the leo i dwarf spheroidal is bound; (v) derive a rotation curve for the large magellanic cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (vi) unveil the dynamical effect of the bar on the motions of stars in the large magellanic cloud.conclusions: all these results highlight the incredible power of the gaia astrometric mission, and in particular of its second data release. full table d.3 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/616/a12 | gaia data release 2. kinematics of globular clusters and dwarf galaxies around the milky way |
we explore in a parameterized manner a very large range of physically plausible equations of state (eoss) for compact stars for matter that is either purely hadronic or that exhibits a phase transition. in particular, we produce two classes of eoss with and without phase transitions, each containing one million eoss. we then impose constraints on the maximum mass (m <2.16 m⊙) and on the dimensionless tidal deformability (λ ∼<800 ) deduced from gw170817, together with recent suggestions of lower limits on λ ∼. exploiting more than 1 09 equilibrium models for each class of eoss, we produce distribution functions of all the stellar properties and determine, among other quantities, the radius that is statistically most probable for any value of the stellar mass. in this way, we deduce that the radius of a purely hadronic neutron star with a representative mass of 1.4 m⊙ is constrained to be 12.00 <r1.4/km <13.45 at a 2 σ confidence level, with a most likely value of r¯1.4=12.39 km ; similarly, the smallest dimensionless tidal deformability is λ∼1.4>375 , again at a 2 σ level. on the other hand, because eoss with a phase transition allow for very compact stars on the so-called "twin-star" branch, small radii are possible with such eoss although not probable, i.e., 8.53 <r1.4/km <13.74 and r¯1.4=13.06 km at a 2 σ level, with λ∼1.4>35.5 at a 3 σ level. finally, since these eoss exhibit upper limits on λ ∼, the detection of a binary with a total mass of 3.4 m⊙ and λ∼1.7>461 can rule out twin-star solutions. | new constraints on radii and tidal deformabilities of neutron stars from gw170817 |
the line emission mapper (lem) is an x-ray probe for the 2030s that will answer the outstanding questions of the universe's structure formation. it will also provide transformative new observing capabilities for every area of astrophysics, and to heliophysics and planetary physics as well. lem's main goal is a comprehensive look at the physics of galaxy formation, including stellar and black-hole feedback and flows of baryonic matter into and out of galaxies. these processes are best studied in x-rays, and emission-line mapping is the pressing need in this area. lem will use a large microcalorimeter array/ifu, covering a 30x30' field with 10" angular resolution, to map the soft x-ray line emission from objects that constitute galactic ecosystems. these include supernova remnants, star-forming regions, superbubbles, galactic outflows (such as the fermi/erosita bubbles in the milky way and their analogs in other galaxies), the circumgalactic medium in the milky way and other galaxies, and the intergalactic medium at the outskirts and beyond the confines of galaxies and clusters. lem's 1-2 ev spectral resolution in the 0.2-2 kev band will make it possible to disentangle the faintest emission lines in those objects from the bright milky way foreground, providing groundbreaking measurements of the physics of these plasmas, from temperatures, densities, chemical composition to gas dynamics. while lem's main focus is on galaxy formation, it will provide transformative capability for all classes of astrophysical objects, from the earth's magnetosphere, planets and comets to the interstellar medium and x-ray binaries in nearby galaxies, agn, and cooling gas in galaxy clusters. in addition to pointed observations, lem will perform a shallow all-sky survey that will dramatically expand the discovery space. | line emission mapper (lem): probing the physics of cosmic ecosystems |
we use deep nirspec spectroscopic data from the jades survey to derive the star formation histories (sfhs) of a sample of 200 galaxies at 0.6$<$z$<$11 and spanning stellar masses from $\rm 10^6$ to $\rm 10^{9.5}~m_\odot$. we find that galaxies at high-redshift, galaxies above the main sequence (ms) and low-mass galaxies tend to host younger stellar populations than their low-redshift, massive, and below the ms counterparts. interestingly, the correlation between age, m$_*$ and sfr existed even earlier than cosmic noon, out to the earliest cosmic epochs. however, these trends have a large scatter. indeed, there are examples of young stellar populations also below the ms, indicating recent (bursty) star formation in evolved systems. we explore further the burstiness of the sfhs by using the ratio between sfr averaged over the last 10 myr and averaged between 10 myr and 100 myr before the epoch of observation ($\mathrm{sfr_{cont, 10}/sfr_{cont, 90}}$). we find that high-redshift and low-mass galaxies have particularly bursty sfhs, while more massive and lower-redshift systems evolve more steadily. we also present the discovery of another (mini-)quenched galaxy at z = 4.4 (in addition to the one at z=7.3 reported by looser et al. 2023), which might be only temporarily quiescent as a consequence of the extremely bursty evolution. finally, we also find a steady decline of dust reddening of the stellar population approaching the earliest cosmic epochs, although some dust reddening is still observed in some of the highest redshift and most star forming systems. | jades: differing assembly histories of galaxies -- observational evidence for bursty sfhs and (mini-)quenching in the first billion years of the universe |
we present a sample of 88 candidate z~8.5-14.5 galaxies selected from the completed nircam imaging from the cosmic evolution early release science (ceers) survey. these data cover ~90 arcmin^2 (10 nircam pointings) in six broad-band and one medium-band imaging filter. with this sample we confirm at higher confidence early jwst conclusions that bright galaxies in this epoch are more abundant than predicted by most theoretical models. we construct the rest-frame ultraviolet luminosity functions at z~9, 11 and 14, and show that the space density of bright (m_uv=-20) galaxies changes only modestly from z~14 to z~9, compared to a steeper increase from z~8 to z~4. while our candidates are photometrically selected, spectroscopic followup has now confirmed 13 of them, with only one significant interloper, implying that the fidelity of this sample is high. successfully explaining the evidence for a flatter evolution in the number densities of uv-bright z>10 galaxies may thus require changes to the dominant physical processes regulating star formation. while our results indicate that significant variations of dust attenuation with redshift are unlikely to be the dominant factor at these high redshifts, they are consistent with predictions from models which naturally have enhanced star-formation efficiency and/or stochasticity. an evolving stellar initial mass function could also bring model predictions into better agreement with our results. deep spectroscopic followup of a large sample of early galaxies can distinguish between these competing scenarios. | the complete ceers early universe galaxy sample: a surprisingly slow evolution of the space density of bright galaxies at z ~ 8.5-14.5 |
context. the second gaia data release (dr2) contains very precise astrometric and photometric properties for more than one billion sources, astrophysical parameters for dozens of millions, radial velocities for millions, variability information for half a million stars from selected variability classes, and orbits for thousands of solar system objects.aims: before the catalogue was published, these data have undergone dedicated validation processes. the goal of this paper is to describe the validation results in terms of completeness, accuracy, and precision of the various gaia dr2 data.methods: the validation processes include a systematic analysis of the catalogue content to detect anomalies, either individual errors or statistical properties, using statistical analysis and comparisons to external data or to models.results: although the astrometric, photometric, and spectroscopic data are of unprecedented quality and quantity, it is shown that the data cannot be used without dedicated attention to the limitations described here, in the catalogue documentation and in accompanying papers. we place special emphasis on the caveats for the statistical use of the data in scientific exploitation. in particular, we discuss the quality filters and the consideration of the properties, systematics, and uncertainties from astrometry to astrophysical parameters, together with the various selection functions. | gaia data release 2. catalogue validation |
the star s2 orbiting the compact radio source sgr a* is a precision probe of the gravitational field around the closest massive black hole (candidate). over the last 2.7 decades we have monitored the star's radial velocity and motion on the sky, mainly with the sinfoni and naco adaptive optics (ao) instruments on the eso vlt, and since 2017, with the four-telescope interferometric beam combiner instrument gravity. in this letter we report the first detection of the general relativity (gr) schwarzschild precession (sp) in s2's orbit. owing to its highly elliptical orbit (e = 0.88), s2's sp is mainly a kink between the pre-and post-pericentre directions of motion ≈±1 year around pericentre passage, relative to the corresponding kepler orbit. the superb 2017-2019 astrometry of gravity defines the pericentre passage and outgoing direction. the incoming direction is anchored by 118 naco-ao measurements of s2's position in the infrared reference frame, with an additional 75 direct measurements of the s2-sgr a* separation during bright states ("flares") of sgr a*. our 14-parameter model fits for the distance, central mass, the position and motion of the reference frame of the ao astrometry relative to the mass, the six parameters of the orbit, as well as a dimensionless parameter fsp for the sp (fsp = 0 for newton and 1 for gr). from data up to the end of 2019 we robustly detect the sp of s2, δϕ ≈ 12' per orbital period. from posterior fitting and mcmc bayesian analysis with different weighting schemes and bootstrapping we find fsp = 1.10 ± 0.19. the s2 data are fully consistent with gr. any extended mass inside s2's orbit cannot exceed ≈0.1% of the central mass. any compact third mass inside the central arcsecond must be less than about 1000 m⊙. | detection of the schwarzschild precession in the orbit of the star s2 near the galactic centre massive black hole |
the extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (pev; 1015 electronvolts) indicates the existence of the so-called pevatrons—cosmic-ray factories that accelerate particles to pev energies. we need to locate and identify such objects to find the origin of galactic cosmic rays1. the principal signature of both electron and proton pevatrons is ultrahigh-energy (exceeding 100 tev) γ radiation. evidence of the presence of a proton pevatron has been found in the galactic centre, according to the detection of a hard-spectrum radiation extending to 0.04 pev (ref. 2). although γ-rays with energies slightly higher than 0.1 pev have been reported from a few objects in the galactic plane3-6, unbiased identification and in-depth exploration of pevatrons requires detection of γ-rays with energies well above 0.1 pev. here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 pev from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than seven standard deviations. despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the pevatrons responsible for the ultrahigh-energy γ-rays have not yet been firmly localized and identified (except for the crab nebula), leaving open the origin of these extreme accelerators. | ultrahigh-energy photons up to 1.4 petaelectronvolts from 12 γ-ray galactic sources |
using backwards ray tracing, we study the shadows of kerr black holes with scalar hair (kbhsh). kbhsh interpolate continuously between kerr bhs and boson stars (bss), so we start by investigating the lensing of light due to bss. moving from the weak to the strong gravity region, bss—which by themselves have no shadows—are classified, according to the lensing produced, as (i) noncompact, which yield not multiple images, (ii) compact, which produce an increasing number of einstein rings and multiple images of the whole celestial sphere, and (iii) ultracompact, which possess light rings, yielding an infinite number of images with (we conjecture) a self-similar structure. the shadows of kbhsh, for kerr-like horizons and noncompact bs-like hair, are analogous to, but distinguishable from, those of comparable kerr bhs. but for non-kerr-like horizons and ultracompact bs-like hair, the shadows of kbhsh are drastically different: novel shapes arise, sizes are considerably smaller, and multiple shadows of a single bh become possible. thus, kbhsh provide quantitatively and qualitatively new templates for ongoing (and future) very large baseline interferometry observations of bh shadows, such as those of the event horizon telescope. | shadows of kerr black holes with scalar hair |
we construct from gaia edr3 an extensive catalogue of spatially resolved binary stars within ≈1 kpc of the sun, with projected separations ranging from a few au to 1 pc. we estimate the probability that each pair is a chance alignment empirically, using the gaia catalogue itself to calculate the rate of chance alignments as a function of observables. the catalogue contains 1.3 (1.1) million binaries with >90 per cent (>99 per cent) probability of being bound, including 16 000 white dwarf - main-sequence (wd + ms) binaries and 1400 wd + wd binaries. we make the full catalogue publicly available, as well as the queries and code to produce it. we then use this sample to calibrate the published gaia dr3 parallax uncertainties, making use of the binary components' near-identical parallaxes. we show that these uncertainties are generally reliable for faint stars (g ≳ 18), but are underestimated significantly for brighter stars. the underestimates are generally $\leq30{{\ \rm per\ cent}}$ for isolated sources with well-behaved astrometry, but are larger (up to ~80 per cent) for apparently well-behaved sources with a companion within ≲4 arcsec, and much larger for sources with poor astrometric fits. we provide an empirical fitting function to inflate published σϖ values for isolated sources. the public catalogue offers wide ranging follow-up opportunities: from calibrating spectroscopic surveys, to precisely constraining ages of field stars, to the masses and the initial-final mass relation of wds, to dynamically probing the galactic tidal field. | a million binaries from gaia edr3: sample selection and validation of gaia parallax uncertainties |
we present mass models of the milky way created to fit observational constraints and to be consistent with expectations from theoretical modelling. the method used to create these models is that demonstrated in our previous study, and we improve on those models by adding gas discs to the potential, considering the effects of allowing the inner slope of the halo density profile to vary, and including new observations of maser sources in the milky way amongst the new constraints. we provide a best-fitting model, as well as estimates of the properties of the milky way. under the assumptions in our main model, we find that the sun is r0 = 8.20 ± 0.09 kpc from the galactic centre, with the circular speed at the sun being v0 = 232.8 ± 3.0 km s-1; and that the galaxy has a total stellar mass of (54.3 ± 5.7) × 109 m⊙, a total virial mass of (1.30 ± 0.30) × 1012 m⊙ and a local dark-matter density of 0.40 ± 0.04 gev cm-3, where the quoted uncertainties are statistical. these values are sensitive to our choice of priors and constraints. we investigate systematic uncertainties, which in some cases may be larger. for example, if we weaken our prior on r0, we find it to be 7.97 ± 0.15 kpc and that v0 = 226.8 ± 4.2 km s-1. we find that most of these properties, including the local dark-matter density, are remarkably insensitive to the assumed power-law density slope at the centre of the dark-matter halo. we find that it is unlikely that the local standard of rest differs significantly from that found under assumptions of axisymmetry. we have made code to compute the force from our potential, and to integrate orbits within it, publicly available. | the mass distribution and gravitational potential of the milky way |
local galaxies are known to broadly follow a bimodal distribution: actively star forming and quiescent systems (i.e. galaxies with no or negligible star formation activity at the epoch of observation). why, when and how such bimodality was established, and whether it has been associated with different processes at different cosmic epochs, is still a key open question in extragalactic astrophysics. directly observing early quiescent galaxies in the primordial universe is therefore of utmost importance to constraining models of galaxy formation and transformation. early quiescent galaxies have been identified out to redshift $z < 5$, and these are all found to be massive ($m_{*}>10^{10}~m_{\odot}$). here we report the discovery of a quiescent galaxy at z$=$7.3, when the universe was only 700 myr old - about 5% of its current age. the jwst/nirspec spectrum of this galaxy from our jades programme exhibits a complete absence of nebular emission lines, while the balmer break and ly$\alpha$ drop are unambiguously detected. we infer that this galaxy experienced a short and intense burst of star formation followed by rapid quenching, about 10-20 myr before the epoch of observation. particularly interesting is that the mass of this quiescent galaxy is only $\sim$4-6$\times 10^8~m_{\odot}$. this mass range is sensitive to various feedback mechanisms that can result in temporary or permanent quiescence. therefore this galaxy represents a unique opportunity to learn more about galaxy formation and transformation in the early universe. | discovery of a quiescent galaxy at z=7.3 |
the deci-hertz interferometer gravitational wave observatory (decigo) is a future japanese space mission with a frequency band of 0.1 hz to 10 hz. decigo aims at the detection of primordial gravitational waves, which could have been produced during the inflationary period right after the birth of the universe. there are many other scientific objectives of decigo, including the direct measurement of the acceleration of the expansion of the universe, and reliable and accurate predictions of the timing and locations of neutron star/black hole binary coalescences. decigo consists of four clusters of observatories placed in heliocentric orbit. each cluster consists of three spacecraft, which form three fabry-pérot michelson interferometers with an arm length of 1000 km. three decigo clusters will be placed far from each other, and the fourth will be placed in the same position as one of the other three to obtain correlation signals for the detection of primordial gravitational waves. we plan to launch b-decigo, which is a scientific pathfinder for decigo, before decigo in the 2030s to demonstrate the technologies required for decigo, as well as to obtain fruitful scientific results to further expand multi-messenger astronomy. | current status of space gravitational wave antenna decigo and b-decigo |
primordial black holes (pbhs) have long been suggested as a viable candidate for the elusive dark matter. the abundance of such pbhs has been constrained using a number of astrophysical observations, except for a hitherto unexplored mass window of mpbh = [10-14, 10-9] solar masses. here we carry out a dense-cadence, 7-hour-long observation of m31 with the subaru hyper suprime-cam (hsc) to search for microlensing of stars in m31 by pbhs lying in the halo regions of the milky way and m31. given our simultaneous monitoring of tens of millions of stars in m31, if such light pbhs make up a significant fraction of dark matter, we expect to find many microlensing events. however, we identify only a single candidate event, which translates into stringent upper bounds on the abundance of pbhs in the mass range mpbh ≃ [10-11, 10-6] solar masses. | microlensing constraints on primordial black holes with subaru/hsc andromeda observations |
we use the data from gaia early data release 3 (edr3) to study the kinematic properties of milky way globular clusters. we measure the mean parallaxes and proper motions (pm) for 170 clusters, determine the pm dispersion profiles for more than 100 clusters, uncover rotation signatures in more than 20 objects, and find evidence for radial or tangential pm anisotropy in a dozen richest clusters. at the same time, we use the selection of cluster members to explore the reliability and limitations of the gaia catalogue itself. we find that the formal uncertainties on parallax and pm are underestimated by $10{-}20{{\ \rm per\ cent}}$ in dense central regions even for stars that pass numerous quality filters. we explore the spatial covariance function of systematic errors, and determine a lower limit on the uncertainty of average parallaxes and pm at the level 0.01 mas and 0.025 mas yr$^{-1}$ , respectively. finally, a comparison of mean parallaxes of clusters with distances from various literature sources suggests that the parallaxes for stars with $g>13$ (after applying the zero-point correction suggested by lindegren et al.) are overestimated by $\sim 0.01\pm 0.003$ mas. despite these caveats, the quality of gaia astrometry has been significantly improved in edr3 and provides valuable insights into the properties of star clusters. | gaia edr3 view on galactic globular clusters |
fast radio bursts (frbs), millisecond-duration bursts prevailing in the radio sky, are the latest large puzzle in the universe and have been a subject of intense observational and theoretical investigations in recent years. the rapid accumulation of observational data has painted the following sketch about the physical origin of frbs: they predominantly originate from cosmological distances, so their sources produce the most extreme coherent radio emission in the universe; at least some, probably most, frbs are repeating sources that do not invoke cataclysmic events; and at least some frbs are produced by magnetars, neutron stars with the strongest magnetic fields in the universe. many open questions regarding the physical origin(s) and mechanism(s) of frbs remain. this review addresses the phenomenology and possible underlying physics of frbs. topics include a summary of the observational data, basic plasma physics, general constraints on frb models from the data, radiation mechanisms, source and environment models, and propagation effects, as well as frbs as cosmological probes. current pressing problems and future prospects are also discussed. | the physics of fast radio bursts |
we use gravitational-wave observations of the binary neutron star merger gw170817 to explore the tidal deformabilities and radii of neutron stars. we perform a bayesian parameter estimation with the source location and distance informed by electromagnetic observations. we also assume that the two stars have the same equation of state; we demonstrate that, for stars with masses comparable to the component masses of gw170817, this is effectively implemented by assuming that the stars' dimensionless tidal deformabilities are determined by the binary's mass ratio q by λ1/λ2=q6. we investigate different choices of prior on the component masses of the neutron stars. we find that the tidal deformability and 90% credible interval is λ ∼ =222-138+420 for a uniform component mass prior, λ ∼ =245-151+453 for a component mass prior informed by radio observations of galactic double neutron stars, and λ ∼ =233-144+448 for a component mass prior informed by radio pulsars. we find a robust measurement of the common areal radius of the neutron stars across all mass priors of 8.9 ≤r ^≤13.2 km , with a mean value of ⟨r ^⟩=10.8 km . our results are the first measurement of tidal deformability with a physical constraint on the star's equation of state and place the first lower bounds on the deformability and areal radii of neutron stars using gravitational waves. | tidal deformabilities and radii of neutron stars from the observation of gw170817 |
at a distance of 1.295 parsecs, the red dwarf proxima centauri (α centauri c, gl 551, hip 70890 or simply proxima) is the sun’s closest stellar neighbour and one of the best-studied low-mass stars. it has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the sun, a measured radius of 14 per cent of the radius of the sun and a mass of about 12 per cent of the mass of the sun. although proxima is considered a moderately active star, its rotation period is about 83 days (ref. 3) and its quiescent activity levels and x-ray luminosity are comparable to those of the sun. here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 earth masses orbiting proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. its equilibrium temperature is within the range where water could be liquid on its surface. | a terrestrial planet candidate in a temperate orbit around proxima centauri |
the large uv/optical/infrared surveyor (luvoir) mission is one of four decadal survey mission concepts studied by nasa in preparation for the us national academies' astro2020 decadal survey. this observatory has the major goal of characterizing a wide range of exoplanets, including those that might be habitable -- or even inhabited. it would simultaneously enable a great leap forward in a broad range of astrophysics -- from the epoch of reionization, through galaxy formation and evolution, to star and planet formation. powerful remote sensing observations of solar system bodies will also be possible. this final report on the luvoir study presents the scientific motivations and goals of the mission concept, the engineering design, and technology development information. please refer to the luvoir final report appendices (separate document) for additional information. | the luvoir mission concept study final report |
nonspherical mass motions are a generic feature of core-collapse supernovae, and hydrodynamic instabilities play a crucial role in the explosion mechanism. the first successful neutrino-driven explosions could be obtained with self-consistent, first-principles simulations in three spatial dimensions. but three-dimensional (3d) models tend to be less prone to explosion than the corresponding axisymmetric two-dimensional (2d) ones. the reason is that 3d turbulence leads to energy cascading from large to small spatial scales, the inverse of the 2d case, thus disfavoring the growth of buoyant plumes on the largest scales. unless the inertia to explode simply reflects a lack of sufficient resolution in relevant regions, some important component of robust and sufficiently energetic neutrino-powered explosions may still be missing. such a deficit could be associated with progenitor properties such as rotation, magnetic fields, or precollapse perturbations, or with microphysics that could cause enhancement of neutrino heating behind the shock. 3d simulations have also revealed new phenomena that are not present in 2d ones, such as spiral modes of the standing accretion shock instability (sasi) and a stunning dipolar lepton-number emission self-sustained asymmetry (lesa). both impose time- and direction-dependent variations on the detectable neutrino signal. the understanding of these effects and of their consequences is still in its infancy. | physics of core-collapse supernovae in three dimensions: a sneak preview |
all ten ligo/virgo binary black hole (bh-bh) coalescences reported following the o1/o2 runs have near-zero effective spins. there are only three potential explanations for this. if the bh spin magnitudes are large, then: (i) either both bh spin vectors must be nearly in the orbital plane or (ii) the spin angular momenta of the bhs must be oppositely directed and similar in magnitude. then there is also the possibility that (iii) the bh spin magnitudes are small. we consider the third hypothesis within the framework of the classical isolated binary evolution scenario of the bh-bh merger formation. we test three models of angular momentum transport in massive stars: a mildly efficient transport by meridional currents (as employed in the geneva code), an efficient transport by the tayler-spruit magnetic dynamo (as implemented in the mesa code), and a very-efficient transport (as proposed by fuller et al.) to calculate natal bh spins. we allow for binary evolution to increase the bh spins through accretion and account for the potential spin-up of stars through tidal interactions. additionally, we update the calculations of the stellar-origin bh masses, including revisions to the history of star formation and to the chemical evolution across cosmic time. we find that we can simultaneously match the observed bh-bh merger rate density and bh masses and bh-bh effective spins. models with efficient angular momentum transport are favored. the updated stellar-mass weighted gas-phase metallicity evolution now used in our models appears to be key for obtaining an improved reproduction of the ligo/virgo merger rate estimate. mass losses during the pair-instability pulsation supernova phase are likely to be overestimated if the merger gw170729 hosts a bh more massive than 50 m⊙. we also estimate rates of black hole-neutron star (bh-ns) mergers from recent ligo/virgo observations. if, in fact. angular momentum transport in massive stars is efficient, then any (electromagnetic or gravitational wave) observation of a rapidly spinning bh would indicate either a very effective tidal spin up of the progenitor star (homogeneous evolution, high-mass x-ray binary formation through case a mass transfer, or a spin- up of a wolf-rayet star in a close binary by a close companion), significant mass accretion by the hole, or a bh formation through the merger of two or more bhs (in a dense stellar cluster). our updated models of bh-bh, bh-ns and ns-ns mergers are now publicly available at http://www.syntheticuniverse.org under the tab "download/2020: double compact objects/<xref ref-type="bibr" rid="r29">http://belczynski et al. 2020</xref>http://" | evolutionary roads leading to low effective spins, high black hole masses, and o1/o2 rates for ligo/virgo binary black holes |
the existence of ∼109m⊙ supermassive black holes (smbhs) within the first billion years of the universe has stimulated numerous ideas for the prompt formation and rapid growth of black holes (bhs) in the early universe. here, we review ways in which the seeds of massive bhs may have first assembled, how they may have subsequently grown as massive as ∼109m⊙, and how multimessenger observations could distinguish between different smbh assembly scenarios. we conclude the following: the ultrarare ∼109 m⊙ smbhs represent only the tip of the iceberg. early bhs likely fill a continuum from the stellar-mass (∼10m⊙) to the supermassive (∼109) regimes, reflecting a range of initial masses and growth histories. stellar-mass bhs were likely left behind by the first generation of stars at redshifts as high as ∼30, but their initial growth typically was stunted due to the shallow potential wells of their host galaxies. conditions in some larger, metal-poor galaxies soon became conducive to the rapid formation and growth of massive seed holes, via gas accretion and by mergers in dense stellar clusters. bh masses depend on the environment (such as the number and properties of nearby radiation sources and the local baryonic streaming velocity) and on the metal enrichment and assembly history of the host galaxy. distinguishing between assembly mechanisms will be difficult, but a combination of observations by the laser interferometer space antenna (probing massive bh growth via mergers) and by deep multiwavelength electromagnetic observations (probing growth via gas accretion) is particularly promising. | the assembly of the first massive black holes |
we compute the radiation reacted momentum impulse δ piμ , spin kick δ siμ, and scattering angle θ between two scattered spinning massive bodies (black holes or neutron stars) using the n =1 supersymmetric worldline quantum field theory formalism up to fourth post-minkowskian (4pm) order. our calculation confirms the state-of-the-art nonspinning results, and extends them to include spin-orbit effects. advanced multiloop feynman integral technology including differential equations and the method of regions are applied and extended to deal with the retarded propagators arising in a causal description of the scattering dynamics. from these results we determine a complete set of radiative fluxes at subleading pm order: the 4pm radiated four-momentum and, via linear response, the 3pm radiated angular momentum, both again including spin-orbit effects. | dissipative scattering of spinning black holes at fourth post-minkowskian order |
observations of neutron-star mergers with distinct messengers, including gravitational waves and electromagnetic signals, can be used to study the behavior of matter denser than an atomic nucleus and to measure the expansion rate of the universe as quantified by the hubble constant. we performed a joint analysis of the gravitational-wave event gw170817 with its electromagnetic counterparts at2017gfo and grb170817a, and the gravitational-wave event gw190425, both originating from neutron-star mergers. we combined these with previous measurements of pulsars using x-ray and radio observations, and nuclear-theory computations using chiral effective field theory, to constrain the neutron-star equation of state. we found that the radius of a 1.4-solar mass neutron star is 11.75-0.81+0.86 km at 90% confidence and the hubble constant is 66.2-4.2+4.4 at 1σ uncertainty. | multimessenger constraints on the neutron-star equation of state and the hubble constant |
the growing field of large-scale time domain astronomy requires methods for probabilistic data analysis that are computationally tractable, even with large data sets. gaussian processes (gps) are a popular class of models used for this purpose, but since the computational cost scales, in general, as the cube of the number of data points, their application has been limited to small data sets. in this paper, we present a novel method for gps modeling in one dimension where the computational requirements scale linearly with the size of the data set. we demonstrate the method by applying it to simulated and real astronomical time series data sets. these demonstrations are examples of probabilistic inference of stellar rotation periods, asteroseismic oscillation spectra, and transiting planet parameters. the method exploits structure in the problem when the covariance function is expressed as a mixture of complex exponentials, without requiring evenly spaced observations or uniform noise. this form of covariance arises naturally when the process is a mixture of stochastically driven damped harmonic oscillators—providing a physical motivation for and interpretation of this choice—but we also demonstrate that it can be a useful effective model in some other cases. we present a mathematical description of the method and compare it to existing scalable gp methods. the method is fast and interpretable, with a range of potential applications within astronomical data analysis and beyond. we provide well-tested and documented open-source implementations of this method in c++, python, and julia. | fast and scalable gaussian process modeling with applications to astronomical time series |
heavy atomic nuclei have an excess of neutrons over protons, which leads to the formation of a neutron skin whose thickness is sensitive to details of the nuclear force. this links atomic nuclei to properties of neutron stars, thereby relating objects that differ in size by orders of magnitude. the nucleus 208pb is of particular interest because it exhibits a simple structure and is experimentally accessible. however, computing such a heavy nucleus has been out of reach for ab initio theory. by combining advances in quantum many-body methods, statistical tools and emulator technology, we make quantitative predictions for the properties of 208pb starting from nuclear forces that are consistent with symmetries of low-energy quantum chromodynamics. we explore 109 different nuclear force parameterizations via history matching, confront them with data in select light nuclei and arrive at an importance-weighted ensemble of interactions. we accurately reproduce bulk properties of 208pb and determine the neutron skin thickness, which is smaller and more precise than a recent extraction from parity-violating electron scattering but in agreement with other experimental probes. this work demonstrates how realistic two- and three-nucleon forces act in a heavy nucleus and allows us to make quantitative predictions across the nuclear landscape. | ab initio predictions link the neutron skin of 208pb to nuclear forces |
the james webb space telescope (jwst) early release observations (eros) is a set of public outreach products created to mark the end of commissioning and the beginning of science operations for jwst. colloquially known as the "webb first images and spectra," these products were intended to demonstrate to the worldwide public that jwst is ready for science, and is capable of producing spectacular results. the package was released on 2022 july 12 and included images and spectra of the galaxy cluster smacs j0723.3-7327 and distant lensed galaxies, the interacting galaxy group stephan's quintet, ngc 3324 in the carina star-forming complex, the southern ring planetary nebula ngc 3132, and the transiting hot jupiter wasp-96b. this paper describes the ero technical design, observations, and scientific processing of data underlying the colorful outreach products. | the jwst early release observations |
the fourth generation of the sloan digital sky survey (sdss-iv) began observations in 2014 july. it pursues three core programs: the apache point observatory galactic evolution experiment 2 (apogee-2), mapping nearby galaxies at apo (manga), and the extended baryon oscillation spectroscopic survey (eboss). as well as its core program, eboss contains two major subprograms: the time domain spectroscopic survey (tdss) and the spectroscopic identification of erosita sources (spiders). this paper describes the first data release from sdss-iv, data release 13 (dr13). dr13 makes publicly available the first 1390 spatially resolved integral field unit observations of nearby galaxies from manga. it includes new observations from eboss, completing the sloan extended quasar, emission-line galaxy, luminous red galaxy survey (sequels), which also targeted variability-selected objects and x-ray-selected objects. dr13 includes new reductions of the sdss-iii boss data, improving the spectrophotometric calibration and redshift classification, and new reductions of the sdss-iii apogee-1 data, improving stellar parameters for dwarf stars and cooler stars. dr13 provides more robust and precise photometric calibrations. value-added target catalogs relevant for eboss, tdss, and spiders and an updated red-clump catalog for apogee are also available. this paper describes the location and format of the data and provides references to important technical papers. the sdss web site, http://www.sdss.org, provides links to the data, tutorials, examples of data access, and extensive documentation of the reduction and analysis procedures. dr13 is the first of a scheduled set that will contain new data and analyses from the planned ∼6 yr operations of sdss-iv. | the 13th data release of the sloan digital sky survey: first spectroscopic data from the sdss-iv survey mapping nearby galaxies at apache point observatory |
on 17 august 2017, gravitational waves (gws) were detected from a binary neutron star merger, gw170817, along with a coincident short gamma-ray burst, grb 170817a. an optical transient source, swope supernova survey 17a (sss17a), was subsequently identified as the counterpart of this event. we present ultraviolet, optical, and infrared light curves of sss17a extending from 10.9 hours to 18 days postmerger. we constrain the radioactively powered transient resulting from the ejection of neutron-rich material. the fast rise of the light curves, subsequent decay, and rapid color evolution are consistent with multiple ejecta components of differing lanthanide abundance. the late-time light curve indicates that sss17a produced at least ~0.05 solar masses of heavy elements, demonstrating that neutron star mergers play a role in rapid neutron capture (r-process) nucleosynthesis in the universe. | light curves of the neutron star merger gw170817/sss17a: implications for r-process nucleosynthesis |
the probe of inflation and cosmic origins (pico) is an imaging polarimeter that will scan the sky for 5 years in 21 frequency bands spread between 21 and 799 ghz. it will produce full-sky surveys of intensity and polarization with a final combined-map noise level of 0.87 $\mu$k arcmin for the required specifications, equivalent to 3300 planck missions, and with our current best-estimate would have a noise level of 0.61 $\mu$k arcmin (6400 planck missions). pico will either determine the energy scale of inflation by detecting the tensor to scalar ratio at a level $r=5\times 10^{-4}~(5\sigma)$, or will rule out with more than $5\sigma$ all inflation models for which the characteristic scale in the potential is the planck scale. with lsst's data it could rule out all models of slow-roll inflation. pico will detect the sum of neutrino masses at $>4\sigma$, constrain the effective number of light particle species with $\delta n_{\rm eff}<0.06~(2\sigma)$, and elucidate processes affecting the evolution of cosmic structures by measuring the optical depth to reionization with errors limited by cosmic variance and by constraining the evolution of the amplitude of linear fluctuations $\sigma_{8}(z)$ with sub-percent accuracy. cross-correlating pico's map of the thermal sunyaev-zeldovich effect with lsst's gold sample of galaxies will precisely trace the evolution of thermal pressure with $z$. pico's maps of the milky way will be used to determine the make up of galactic dust and the role of magnetic fields in star formation efficiency. with 21 full sky legacy maps in intensity and polarization, which cannot be obtained in any other way, the mission will enrich many areas of astrophysics. pico is the only single-platform instrument with the combination of sensitivity, angular resolution, frequency bands, and control of systematic effects that can deliver this compelling, timely, and broad science. | pico: probe of inflation and cosmic origins |
we present phangs-alma, the first survey to map co j = 2 → 1 line emission at ~1″ ~100 pc spatial resolution from a representative sample of 90 nearby (d ≲ 20 mpc) galaxies that lie on or near the z = 0 "main sequence" of star-forming galaxies. co line emission traces the bulk distribution of molecular gas, which is the cold, star-forming phase of the interstellar medium. at the resolution achieved by phangs-alma, each beam reaches the size of a typical individual giant molecular cloud, so that these data can be used to measure the demographics, life cycle, and physical state of molecular clouds across the population of galaxies where the majority of stars form at z = 0. this paper describes the scientific motivation and background for the survey, sample selection, global properties of the targets, atacama large millimeter/submillimeter array (alma) observations, and characteristics of the delivered data and derived data products. as the alma sample serves as the parent sample for parallel surveys with muse on the very large telescope, the hubble space telescope, astrosat, the very large array, and other facilities, we include a detailed discussion of the sample selection. we detail the estimation of galaxy mass, size, star formation rate, co luminosity, and other properties, compare estimates using different systems and provide best-estimate integrated measurements for each target. we also report the design and execution of the alma observations, which combine a cycle 5 large program, a series of smaller programs, and archival observations. finally, we present the first 1″ resolution atlas of co emission from nearby galaxies and describe the properties and contents of the first phangs-alma public data release. | phangs-alma: arcsecond co(2-1) imaging of nearby star-forming galaxies |
using the n =1 supersymmetric, spinning worldline quantum field theory formalism, we compute the conservative spin-orbit part of the momentum impulse δ piμ , spin kick δ siμ, and scattering angle θ from the scattering of two spinning massive bodies (black holes or neutron stars) up to fourth post-minkowskian (pm) order. these three-loop results extend the state of the art for generically spinning binaries from 3pm to 4pm. they are obtained by employing recursion relations for the integrand construction and advanced multiloop feynman integral technology in the causal (in-in) worldline quantum field theory framework to directly produce classical observables. we focus on the conservative contribution (including tail effects) and outline the computations for the dissipative contributions as well. our spin-orbit results agree with next-to-next-to-next-to-leading-order post-newtonian and test-body data in the respective limits. we also reconfirm the conservative 4pm nonspinning results. | conservative scattering of spinning black holes at fourth post-minkowskian order |
distant quasars are unique tracers to study the formation of the earliest supermassive black holes (smbhs) and the history of cosmic reionization. despite extensive efforts, only two quasars have been found at z ≥ 7.5, due to a combination of their low spatial density and the high contamination rate in quasar selection. we report the discovery of a luminous quasar at z = 7.642, j0313-1806, the most distant quasar yet known. this quasar has a bolometric luminosity of 3.6 × 1013l⊙. deep spectroscopic observations reveal a smbh with a mass of (1.6 ± 0.4) × 109 m⊙ in this quasar. the existence of such a massive smbh just ∼670 million years after the big bang challenges significantly theoretical models of smbh growth. in addition, the quasar spectrum exhibits strong broad absorption line (bal) features in c iv and si iv, with a maximum velocity close to 20% of the speed of light. the relativistic bal features, combined with a strongly blueshifted c iv emission line, indicate that there is a strong active galactic nucleus (agn)-driven outflow in this system. atacama large millimeter/submillimeter array observations detect the dust continuum and [c ii] emission from the quasar host galaxy, yielding an accurate redshift of 7.6423 ± 0.0013 and suggesting that the quasar is hosted by an intensely star-forming galaxy, with a star formation rate of ∼200 m⊙ yr-1 and a dust mass of ∼7 × 107 m⊙. follow-up observations of this reionization-era bal quasar will provide a powerful probe of the effects of agn feedback on the growth of the earliest massive galaxies. | a luminous quasar at redshift 7.642 |
in recent years our understanding of the dense matter equation of state (eos) of neutron stars has significantly improved by analyzing multimessenger data from radio/x-ray pulsars, gravitational wave events, and from nuclear physics constraints. here we study the additional impact on the eos from the jointly estimated mass and radius of psr j0740+6620, presented in riley et al. by analyzing a combined data set from x-ray telescopes nicer and xmm-newton. we employ two different high-density eos parameterizations: a piecewise-polytropic (pp) model and a model based on the speed of sound in a neutron star (cs). at nuclear densities these are connected to microscopic calculations of neutron matter based on chiral effective field theory (eft) interactions. in addition to the new nicer data for this heavy neutron star, we separately study constraints from the radio timing mass measurement of psr j0740+6620, the gravitational wave events of binary neutron stars gw190425 and gw170817, and for the latter the associated kilonova at2017gfo. by combining all these, and the nicer mass-radius estimate of psr j0030+0451, we find the radius of a 1.4 m⊙ neutron star to be constrained to the 95% credible ranges ${12.33}_{-0.81}^{+0.76}\,\mathrm{km}$ (pp model) and ${12.18}_{-0.79}^{+0.56}\,\mathrm{km}$ (cs model). in addition, we explore different chiral eft calculations and show that the new nicer results provide tight constraints for the pressure of neutron star matter at around twice saturation density, which shows the power of these observations to constrain dense matter interactions at intermediate densities. | constraints on the dense matter equation of state and neutron star properties from nicer's mass-radius estimate of psr j0740+6620 and multimessenger observations |
in recent years our understanding of neutron stars has advanced remarkably, thanks to research converging from many directions. the importance of understanding neutron star behavior and structure has been underlined by the recent direct detection of gravitational radiation from merging neutron stars. the clean identification of several heavy neutron stars, of order two solar masses, challenges our current understanding of how dense matter can be sufficiently stiff to support such a mass against gravitational collapse. programs underway to determine simultaneously the mass and radius of neutron stars will continue to constrain and inform theories of neutron star interiors. at the same time, an emerging understanding in quantum chromodynamics (qcd) of how nuclear matter can evolve into deconfined quark matter at high baryon densities is leading to advances in understanding the equation of state of the matter under the extreme conditions in neutron star interiors. we review here the equation of state of matter in neutron stars from the solid crust through the liquid nuclear matter interior to the quark regime at higher densities. we focus in detail on the question of how quark matter appears in neutron stars, and how it affects the equation of state. after discussing the crust and liquid nuclear matter in the core we briefly review aspects of microscopic quark physics relevant to neutron stars, and quark models of dense matter based on the nambu-jona-lasinio framework, in which gluonic processes are replaced by effective quark interactions. we turn then to describing equations of state useful for interpretation of both electromagnetic and gravitational observations, reviewing the emerging picture of hadron-quark continuity in which hadronic matter turns relatively smoothly, with at most only a weak first order transition, into quark matter with increasing density. we review construction of unified equations of state that interpolate between the reasonably well understood nuclear matter regime at low densities and the quark matter regime at higher densities. the utility of such interpolations is driven by the present inability to calculate the dense matter equation of state in qcd from first principles. as we review, the parameters of effective quark models—which have direct relevance to the more general structure of the qcd phase diagram of dense and hot matter—are constrained by neutron star mass and radii measurements, in particular favoring large repulsive density-density and attractive diquark pairing interactions. we describe the structure of neutron stars constructed from the unified equations of states with crossover. lastly we present the current equations of state—called ‘qhc18’ for quark-hadron crossover—in a parametrized form practical for neutron star modeling. | from hadrons to quarks in neutron stars: a review |
during the first 500 million years of cosmic history, the first stars and galaxies formed, seeding the universe with heavy elements and eventually reionizing the intergalactic medium1-3. observations with the james webb space telescope (jwst) have uncovered a surprisingly high abundance of candidates for early star-forming galaxies, with distances (redshifts, z), estimated from multiband photometry, as large as z ≈ 16, far beyond pre-jwst limits4-9. although such photometric redshifts are generally robust, they can suffer from degeneracies and occasionally catastrophic errors. spectroscopic measurements are required to validate these sources and to reliably quantify physical properties that can constrain galaxy formation models and cosmology10. here we present jwst spectroscopy that confirms redshifts for two very luminous galaxies with z > 11, and also demonstrates that another candidate with suggested z ≈ 16 instead has z = 4.9, with an unusual combination of nebular line emission and dust reddening that mimics the colours expected for much more distant objects. these results reinforce evidence for the early, rapid formation of remarkably luminous galaxies while also highlighting the necessity of spectroscopic verification. the large abundance of bright, early galaxies may indicate shortcomings in current galaxy formation models or deviations from physical properties (such as the stellar initial mass function) that are generally believed to hold at later times. | confirmation and refutation of very luminous galaxies in the early universe |
fast radio bursts are astronomical radio flashes of unknown physical nature with durations of milliseconds. their dispersive arrival times suggest an extragalactic origin and imply radio luminosities that are orders of magnitude larger than those of all known short-duration radio transients. so far all fast radio bursts have been detected with large single-dish telescopes with arcminute localizations, and attempts to identify their counterparts (source or host galaxy) have relied on the contemporaneous variability of field sources or the presence of peculiar field stars or galaxies. these attempts have not resulted in an unambiguous association with a host or multi-wavelength counterpart. here we report the subarcsecond localization of the fast radio burst frb 121102, the only known repeating burst source, using high-time-resolution radio interferometric observations that directly image the bursts. our precise localization reveals that frb 121102 originates within 100 milliarcseconds of a faint 180-microjansky persistent radio source with a continuum spectrum that is consistent with non-thermal emission, and a faint (twenty-fifth magnitude) optical counterpart. the flux density of the persistent radio source varies by around ten per cent on day timescales, and very long baseline radio interferometry yields an angular size of less than 1.7 milliarcseconds. our observations are inconsistent with the fast radio burst having a galactic origin or its source being located within a prominent star-forming galaxy. instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. localization and identification of a host or counterpart has been essential to understanding the origins and physics of other kinds of transient events, including gamma-ray bursts and tidal disruption events. however, if other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct subarcsecond localizations may be the only way to provide reliable associations. | a direct localization of a fast radio burst and its host |
one of the main goals of the jwst is to study the first galaxies in the universe. we present a systematic photometric analysis of very distant galaxies in the first jwst deep field towards the massive lensing cluster smacs0723. as a result, we report the discovery of two galaxy candidates at z ~ 16, only 250 million years after the big bang. we also identify two candidates at z ~ 12 and six candidates at z ~ 9-11. our search extended out to z ≲ 21 by combining colour information across seven near-infrared camera and near-infrared imager and slitless spectrograph filters. by modelling the spectral energy distributions (seds) with eazy and beagle, we test the robustness of the photometric redshift estimates. while their intrinsic (unlensed) luminosity is typical of the characteristic luminosity l* at z > 10, our high-redshift galaxies typically show small sizes and their morphologies are consistent with disks in some cases. the highest-redshift candidates have extremely blue ultraviolet-continuum slopes -3 < β < -2.4, young ages ~10-100 myr, and stellar masses around log (m⋆/m⊙) = 8.8 inferred from their spectral energy distribution modelling, which indicate a rapid build-up of their stellar mass. our search clearly demonstrates the capabilities of jwst to uncover robust photometric candidates up to very high redshifts and peer into the formation epoch of the first galaxies. | revealing galaxy candidates out to z 16 with jwst observations of the lensing cluster smacs0723 |
the merger of two massive (about 30 solar masses) black holes has been detected in gravitational waves. this discovery validates recent predictions that massive binary black holes would constitute the first detection. previous calculations, however, have not sampled the relevant binary-black-hole progenitors—massive, low-metallicity binary stars—with sufficient accuracy nor included sufficiently realistic physics to enable robust predictions to better than several orders of magnitude. here we report high-precision numerical simulations of the formation of binary black holes via the evolution of isolated binary stars, providing a framework within which to interpret the first gravitational-wave source, gw150914, and to predict the properties of subsequent binary-black-hole gravitational-wave events. our models imply that these events form in an environment in which the metallicity is less than ten per cent of solar metallicity, and involve stars with initial masses of 40-100 solar masses that interact through mass transfer and a common-envelope phase. these progenitor stars probably formed either about 2 billion years or, with a smaller probability, 11 billion years after the big bang. most binary black holes form without supernova explosions, and their spins are nearly unchanged since birth, but do not have to be parallel. the classical field formation of binary black holes we propose, with low natal kicks (the velocity of the black hole at birth) and restricted common-envelope evolution, produces approximately 40 times more binary-black-holes mergers than do dynamical formation channels involving globular clusters; our predicted detection rate of these mergers is comparable to that from homogeneous evolution channels. our calculations predict detections of about 1,000 black-hole mergers per year with total masses of 20-80 solar masses once second-generation ground-based gravitational-wave observatories reach full sensitivity. | the first gravitational-wave source from the isolated evolution of two stars in the 40-100 solar mass range |
this overview paper describes the legacy prospect and discovery potential of the dark energy survey (des) beyond cosmological studies, illustrating it with examples from the des early data. des is using a wide-field camera (decam) on the 4 m blanco telescope in chile to image 5000 sq deg of the sky in five filters (grizy). by its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. in addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of type ia supernovae and other transients. the main goals of des are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and type ia supernovae. however, des also provides a rich data set which allows us to study many other aspects of astrophysics. in this paper, we focus on additional science with des, emphasizing areas where the survey makes a difference with respect to other current surveys. the paper illustrates, using early data (from `science verification', and from the first, second and third seasons of observations), what des can tell us about the solar system, the milky way, galaxy evolution, quasars and other topics. in addition, we show that if the cosmological model is assumed to be λ+cold dark matter, then important astrophysics can be deduced from the primary des probes. highlights from des early data include the discovery of 34 trans-neptunian objects, 17 dwarf satellites of the milky way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed). | the dark energy survey: more than dark energy - an overview |
fast radio bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances. previous follow-up observations have failed to find additional bursts at the same dispersion measure (that is, the integrated column density of free electrons between source and telescope) and sky position as the original detections. the apparent non-repeating nature of these bursts has led to the suggestion that they originate in cataclysmic events. here we report observations of ten additional bursts from the direction of the fast radio burst frb 121102. these bursts have dispersion measures and sky positions consistent with the original burst. this unambiguously identifies frb 121102 as repeating and demonstrates that its source survives the energetic events that cause the bursts. additionally, the bursts from frb 121102 show a wide range of spectral shapes that appear to be predominantly intrinsic to the source and which vary on timescales of minutes or less. although there may be multiple physical origins for the population of fast radio bursts, these repeat bursts with high dispersion measure and variable spectra specifically seen from the direction of frb 121102 support an origin in a young, highly magnetized, extragalactic neutron star. | a repeating fast radio burst |
the transiting exoplanet survey satellite (tess) will be conducting a nearly all-sky photometric survey over two years, with a core mission goal to discover small transiting exoplanets orbiting nearby bright stars. it will obtain 30 minute cadence observations of all objects in the tess fields of view, along with two-minute cadence observations of 200,000-400,000 selected stars. the choice of which stars to observe at the two-minute cadence is driven by the need to detect small transiting planets, which leads to the selection of primarily bright, cool dwarfs. we describe the catalogs assembled and the algorithms used to populate the tess input catalog (tic), including plans to update the tic with the incorporation of the gaia second data release in the near future. we also describe a ranking system for prioritizing stars according to the smallest transiting planet detectable, and assemble a candidate target list (ctl) using that ranking. we discuss additional factors that affect the ability to photometrically detect and dynamically confirm small planets, and we note additional stellar populations of interest that may be added to the final target list. the tic is available on the stsci mast server, and an enhanced ctl is available through the filtergraph data visualization portal system at the url http://filtergraph.com/tess_ctl. | the tess input catalog and candidate target list |
we derive supernova (sn) bounds on muon-philic bosons, taking advantage of the recent emergence of muonic sn models. our main innovations are to consider scalars ϕ in addition to pseudoscalars a and to include systematically the generic two-photon coupling gγ γ implied by a muon triangle loop. this interaction allows for primakoff scattering and radiative boson decays. the globular-cluster bound gγ γ<0.67 ×10-10 gev-1 carries over to the muonic yukawa couplings as ga<3.1 ×10-9 and gϕ<4.6 ×10-9 for ma ,ϕ≲100 kev , so sn arguments become interesting mainly for larger masses. if bosons escape freely from the sn core the main constraints originate from sn 1987a γ rays and the diffuse cosmic γ -ray background. the latter allows at most 10-4 of a typical total sn energy of esn≃3 ×1053 erg to show up as γ rays, for ma ,ϕ≳100 kev implying ga≲0.9 ×10-10 and gϕ≲0.4 ×10-10. in the trapping regime the bosons emerge as quasi-thermal radiation from a region near the neutrino sphere and match lν for ga ,ϕ≃10-4. however, the 2 γ decay is so fast that all the energy is dumped into the surrounding progenitor-star matter, whereas at most 10-2esn may show up in the explosion. to suppress boson emission below this level we need yet larger couplings, ga≳2 ×10-3 and gϕ≳4 ×10-3. muonic scalars can explain the muon magnetic-moment anomaly for gϕ≃0.4 ×10-3, a value hard to reconcile with sn physics despite the uncertainty of the explosion-energy bound. for generic axionlike particles, this argument covers the "cosmological triangle" in the ga γ γ- ma parameter space. | muonic boson limits: supernova redux |
we present an improved estimate of the occurrence rate of small planets orbiting small stars by searching the full four-year kepler data set for transiting planets using our own planet detection pipeline and conducting transit injection and recovery simulations to empirically measure the search completeness of our pipeline. we identified 156 planet candidates, including one object that was not previously identified as a kepler object of interest. we inspected all publicly available follow-up images, observing notes, and centroid analyses, and corrected for the likelihood of false positives. we evaluated the sensitivity of our detection pipeline on a star-by-star basis by injecting 2000 transit signals into the light curve of each target star. for periods shorter than 50 days, we find {0.56}-0.05+0.06 earth-size planets (1-1.5 r⊕) and {0.46}-0.05+0.07 super-earths (1.5-2 r⊕) per m dwarf. in total, we estimate a cumulative planet occurrence rate of 2.5 ± 0.2 planets per m dwarf with radii 1-4 r⊕ and periods shorter than 200 days. within a conservatively defined habitable zone (hz) based on the moist greenhouse inner limit and maximum greenhouse outer limit, we estimate an occurrence rate of {0.16}-0.07+0.17 earth-size planets and {0.12}-0.05+0.10 super-earths per m dwarf hz. adopting the broader insolation boundaries of the recent venus and early mars limits yields a higher estimate of {0.24}-0.08+0.18 earth-size planets and {0.21}-0.06+0.11 super-earths per m dwarf hz. this suggests that the nearest potentially habitable non-transiting and transiting earth-size planets are 2.6 ± 0.4 pc and {10.6}-1.8+1.6 pc away, respectively. if we include super-earths, these distances diminish to 2.1 ± 0.2 pc and {8.6}-0.8+0.7 pc. | the occurrence of potentially habitable planets orbiting m dwarfs estimated from the full kepler dataset and an empirical measurement of the detection sensitivity |
the orbital observatory spectrum-roentgen-gamma (srg), equipped with the grazing-incidence x-ray telescopes mikhail pavlinsky art-xc and erosita, was launched by roscosmos to the lagrange l2 point of the sun-earth system on july 13, 2019. the launch was carried out from the baikonur cosmodrome by a proton-m rocket with a dm-03 upper stage. the german telescope erosita was installed on srg under an agreement between roskosmos and the dlr, the german aerospace agency. in december 2019, srg started to perform its main scientific task: scanning the celestial sphere to obtain x-ray maps of the entire sky in several energy ranges (from 0.2 to 8 kev with erosita, and from 4 to 30 kev with art-xc). by mid-june 2021, the third six-month all-sky survey had been completed. over a period of four years, it is planned to obtain eight independent maps of the entire sky in each of the energy ranges. the sum of these maps will provide high sensitivity and reveal more than three million quasars and over one hundred thousand massive galaxy clusters and galaxy groups. the availability of eight sky maps will enable monitoring of long-term variability (every six months) of a huge number of extragalactic and galactic x-ray sources, including hundreds of thousands of stars with hot coronae. in addition, the rotation of the satellite around the axis directed toward the sun with a period of four hours enables tracking the faster variability of bright x-ray sources during one day every half year. the chosen strategy of scanning the sky leads to the formation of deep survey zones near both ecliptic poles. the paper presents sky maps obtained by the telescopes on board srg during the first survey of the entire sky and a number of results of deep observations performed during the flight to the l2 point in the frame of the performance verification program, demonstrating the capabilities of the observatory in imaging, spectroscopy, and timing of x-ray sources. it is planned that in december 2023, the observatory will for at least two years switch to observations of the most interesting sources in the sky in triaxial orientation mode and deep scanning of selected celestial fields with an area of up to 150 square degrees. these modes of operation were tested during the performance verification phase. every day, data from the srg observatory are dumped onto the largest antennas of the russian deep space network in bear lakes and near ussuriysk. | srg x-ray orbital observatory. its telescopes and first scientific results |
star clusters stand at the intersection of much of modern astrophysics: the ism, gravitational dynamics, stellar evolution, and cosmology. here, we review observations and theoretical models for the formation, evolution, and eventual disruption of star clusters. current literature suggests a picture of this life cycle including the following several phases: clusters form in hierarchically structured, accreting molecular clouds that convert gas into stars at a low rate per dynamical time until feedback disperses the gas. the densest parts of the hierarchy resist gas removal long enough to reach high star-formation efficiency, becoming dynamically relaxed and well mixed. these remain bound after gas removal. in the first ∼100 myr after gas removal, clusters disperse moderately fast, through a combination of mass loss and tidal shocks by dense molecular structures in the star-forming environment. after ∼100 myr, clusters lose mass via two-body relaxation and shocks by giant molecular clouds, processes that preferentially affect low-mass clusters and cause a turnover in the cluster mass function to appear on ∼1-10-gyr timescales. even after dispersal, some clusters remain coherent and thus detectable in chemical or action space for multiple galactic orbits.in the next decade, a new generation of space- and adaptive optics-assisted ground-based telescopes will enable us to test and refine this picture. | star clusters across cosmic time |
we update the capabilities of the open-knowledge software instrument modules for experiments in stellar astrophysics (mesa). the new auto_diff module implements automatic differentiation in mesa, an enabling capability that alleviates the need for hard-coded analytic expressions or finite-difference approximations. we significantly enhance the treatment of the growth and decay of convection in mesa with a new model for time-dependent convection, which is particularly important during late-stage nuclear burning in massive stars and electron-degenerate ignition events. we strengthen mesa's implementation of the equation of state, and we quantify continued improvements to energy accounting and solver accuracy through a discussion of different energy equation features and enhancements. to improve the modeling of stars in mesa, we describe key updates to the treatment of stellar atmospheres, molecular opacities, compton opacities, conductive opacities, element diffusion coefficients, and nuclear reaction rates. we introduce treatments of starspots, an important consideration for low-mass stars, and modifications for superadiabatic convection in radiation-dominated regions. we describe new approaches for increasing the efficiency of calculating monochromatic opacities and radiative levitation, and for increasing the efficiency of evolving the late stages of massive stars with a new operator-split nuclear burning mode. we close by discussing major updates to mesa's software infrastructure that enhance source code development and community engagement. | modules for experiments in stellar astrophysics (mesa): time-dependent convection, energy conservation, automatic differentiation, and infrastructure |
globular clusters (gcs) exhibit star-to-star variations in specific elements (e.g., he, c, n, o, na, al) that bear the hallmark of high-temperature h-burning. these abundance variations can be observed spectroscopically and also photometrically, with the appropriate choice of filters, due to the changing of spectral features within the band pass. this phenomenon is observed in nearly all of the ancient gcs, although, to date, it has not been found in any massive cluster younger than 2 gyr. many scenarios have been suggested to explain this phenomenon, with most invoking multiple epochs of star formation within the cluster; however, all have failed to reproduce various key observations, in particular when a global view of the gc population is taken. we review the state of current observations and outline the successes and failures of each of the main proposed models. the traditional idea of using the stellar ejecta from a first generation of stars to form a second generation of stars, while conceptually straightforward, has failed to reproduce an increasing number of observational constraints. we conclude that the puzzle of multiple populations remains unsolved, hence alternative theories are needed. | multiple stellar populations in globular clusters |
scalarization is a mechanism that endows strongly self-gravitating bodies, such as neutron stars and black holes, with a scalar field configuration. it resembles a phase transition in that the scalar configuration only appears when a certain quantity that characterizes the compact object, e.g., its compactness or spin, is beyond a threshold. we provide a critical and comprehensive review of scalarization, including the mechanism itself, theories that exhibit it, its manifestation in neutron stars, black holes, and their binaries, potential extension to other fields, and a thorough discussion of future perspectives. | scalarization |
fast radio bursts (frbs) are flashes of unknown physical origin1. the majority of frbs have been seen only once, although some are known to generate multiple flashes2,3. many models invoke magnetically powered neutron stars (magnetars) as the source of the emission4,5. recently, the discovery6 of another repeater (frb 20200120e) was announced, in the direction of the nearby galaxy m81, with four potential counterparts at other wavelengths6. here we report observations that localized the frb to a globular cluster associated with m81, where it is 2 parsecs away from the optical centre of the cluster. globular clusters host old stellar populations, challenging frb models that invoke young magnetars formed in a core-collapse supernova. we propose instead that frb 20200120e originates from a highly magnetized neutron star formed either through the accretion-induced collapse of a white dwarf, or the merger of compact stars in a binary system7. compact binaries are efficiently formed inside globular clusters, so a model invoking them could also be responsible for the observed bursts. | a repeating fast radio burst source in a globular cluster |
context. gaia data release 1 (dr1) contains astrometric results for more than 1 billion stars brighter than magnitude 20.7 based on observations collected by the gaia satellite during the first 14 months of its operational phase.aims: we give a brief overview of the astrometric content of the data release and of the model assumptions, data processing, and validation of the results.methods: for stars in common with the hipparcos and tycho-2 catalogues, complete astrometric single-star solutions are obtained by incorporating positional information from the earlier catalogues. for other stars only their positions are obtained, essentially by neglecting their proper motions and parallaxes. the results are validated by an analysis of the residuals, through special validation runs, and by comparison with external data.results: for about two million of the brighter stars (down to magnitude 11.5) we obtain positions, parallaxes, and proper motions to hipparcos-type precision or better. for these stars, systematic errors depending for example on position and colour are at a level of ± 0.3 milliarcsecond (mas). for the remaining stars we obtain positions at epoch j2015.0 accurate to 10 mas. positions and proper motions are given in a reference frame that is aligned with the international celestial reference frame (icrf) to better than 0.1 mas at epoch j2015.0, and non-rotating with respect to icrf to within 0.03 mas yr-1. the hipparcos reference frame is found to rotate with respect to the gaia dr1 frame at a rate of 0.24 mas yr-1.conclusions: based on less than a quarter of the nominal mission length and on very provisional and incomplete calibrations, the quality and completeness of the astrometric data in gaia dr1 are far from what is expected for the final mission products. the present results nevertheless represent a huge improvement in the available fundamental stellar data and practical definition of the optical reference frame. | gaia data release 1. astrometry: one billion positions, two million proper motions and parallaxes |
this paper provides an update of our previous scaling relations between galaxy-integrated molecular gas masses, stellar masses, and star formation rates (sfrs), in the framework of the star formation main sequence (ms), with the main goal of testing for possible systematic effects. for this purpose our new study combines three independent methods of determining molecular gas masses from co line fluxes, far-infrared dust spectral energy distributions, and ∼1 mm dust photometry, in a large sample of 1444 star-forming galaxies between z = 0 and 4. the sample covers the stellar mass range log(m */m ⊙) = 9.0-11.8, and sfrs relative to that on the ms, δms = sfr/sfr(ms), from 10-1.3 to 102.2. our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero-point offsets are minimized and uncertainties are properly taken into account. the molecular gas depletion time t depl, defined as the ratio of molecular gas mass to sfr, scales as (1 + z)-0.6 × (δms)-0.44 and is only weakly dependent on stellar mass. the ratio of molecular to stellar mass μ gas depends on (1+z{)}2.5× {(δ {ms})}0.52× {({m}* )}-0.36, which tracks the evolution of the specific sfr. the redshift dependence of μ gas requires a curvature term, as may the mass dependences of t depl and μ gas. we find no or only weak correlations of t depl and μ gas with optical size r or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high z. based on observations of an iram legacy program carried out with the noema, operated by the institute for radio astronomy in the millimetre range (iram), which is funded by a partnership of insu/cnrs (france), mpg (germany), and ign (spain). | phibss: unified scaling relations of gas depletion time and molecular gas fractions |
context. gaia data release 3 (gaia dr3) contains the second release of the combined radial velocities. it is based on the spectra collected during the first 34 months of the nominal mission. the longer time baseline and the improvements of the pipeline made it possible to push the processing limit from grvs = 12 in gaia dr2 to grvs = 14 mag.aims: we describe the new functionalities implemented for gaia dr3, the quality filters applied during processing and post-processing, and the properties and performance of the published velocities.methods: for gaia dr3, several functionalities were upgraded or added to the spectroscopic pipeline. the calibrations were improved in order to better model the temporal evolution of the straylight and of the instrumental point spread function (psf). the overlapped spectra, which were mostly discarded in gaia dr2, are now handled by a dedicated module. the hot star template mismatch, which prevented publication of hot stars in gaia dr2, is largely mitigated now, down to grvs = 12 mag. the combined radial velocity of stars brighter than or equal to grvs = 12 mag is calculated in the same way as in gaia dr2, that is, as the median of the epoch radial velocity time series. the combined radial velocity of the fainter stars is measured from the average of the cross-correlation functions.results: gaia dr3 contains the combined radial velocities of 33 812 183 stars. with respect to gaia dr2, the temperature interval has been expanded from teff ∈ [3600, 6750] k to teff ∈ [3100, 14 500] k for the bright stars (grvs ≤ 12 mag) and [3100, 6750] k for the fainter stars. the radial velocities sample a significant part of the milky way: they reach a few kiloparsecs beyond the galactic centre in the disc and up to about 10−15 kpc vertically into the inner halo. the median formal precision of the velocities is 1.3 km s−1 at grvs = 12 and 6.4 km s−1 at grvs = 14 mag. the velocity zeropoint exhibits a small systematic trend with magnitude that starts around grvs = 11 mag and reaches about 400 m s−1 at grvs = 14 mag. a correction formula is provided that can be applied to the published data. the gaia dr3 velocity scale agrees satisfactorily with apogee, galah, ges, and rave; the systematic differences mostly remain below a few hundred m s−1. the properties of the radial velocities are also illustrated with specific objects: open clusters, globular clusters, and the large magellanic cloud. for example, the precision of the data allows mapping the line-of-sight rotational velocities of the globular cluster 47 tuc and of the large magellanic cloud. | gaia data release 3. properties and validation of the radial velocities |
the onset of galaxy formation is thought to be initiated by the infall of neutral, pristine gas onto the first protogalactic halos. however, direct constraints on the abundance of neutral atomic hydrogen (hi) in galaxies have been difficult to obtain at early cosmic times. here we present spectroscopic observations with jwst of three galaxies at redshifts $z=8.8 - 11.4$, about $400-600$ myr after the big bang, that show strong damped lyman-$\alpha$ absorption ($n_{\rm hi} > 10^{22}$ cm$^{-2}$) from hi in their local surroundings, an order of magnitude in excess of the lyman-$\alpha$ absorption caused by the neutral intergalactic medium at these redshifts. consequently, these early galaxies cannot be contributing significantly to reionization, at least at their current evolutionary stages. simulations of galaxy formation show that such massive gas reservoirs surrounding young galaxies so early in the history of the universe is a signature of galaxy formation in progress. | extreme damped lyman-$\\alpha$ absorption in young star-forming galaxies at $z=9-11$ |
the discovery of radio pulsars over a half century ago was a seminal moment in astronomy. it demonstrated the existence of neutron stars, gave a powerful observational tool to study them, and has allowed us to probe strong gravity, dense matter, and the interstellar medium. more recently, pulsar surveys have led to the serendipitous discovery of fast radio bursts (frbs). while frbs appear similar to the individual pulses from pulsars, their large dispersive delays suggest that they originate from far outside the milky way and hence are many orders-of-magnitude more luminous. while most frbs appear to be one-off, perhaps cataclysmic events, two sources are now known to repeat and thus clearly have a longer lived central engine. beyond understanding how they are created, there is also the prospect of using frbs—as with pulsars—to probe the extremes of the universe as well as the otherwise invisible intervening medium. such studies will be aided by the high-implied all-sky event rate: there is a detectable frb roughly once every minute occurring somewhere on the sky. the fact that less than a hundred frb sources have been discovered in the last decade is largely due to the small fields-of-view of current radio telescopes. a new generation of wide-field instruments is now coming online, however, and these will be capable of detecting multiple frbs per day. we are thus on the brink of further breakthroughs in the short-duration radio transient phase space, which will be critical for differentiating between the many proposed theories for the origin of frbs. in this review, we give an observational and theoretical introduction at a level that is accessible to astronomers entering the field. | fast radio bursts |
we report the discovery and monitoring of the near-infrared counterpart (at2017gfo) of a binary neutron-star merger event detected as a gravitational wave source by advanced laser interferometer gravitational-wave observatory (ligo)/virgo (gw170817) and as a short gamma-ray burst by fermi gamma-ray burst monitor (gbm) and integral spi-acs (grb 170817a). the evolution of the transient light is consistent with predictions for the behavior of a “kilonova/macronova” powered by the radioactive decay of massive neutron-rich nuclides created via r-process nucleosynthesis in the neutron-star ejecta. in particular, evidence for this scenario is found from broad features seen in hubble space telescope infrared spectroscopy, similar to those predicted for lanthanide-dominated ejecta, and the much slower evolution in the near-infrared {k}{{s}}-band compared to the optical. this indicates that the late-time light is dominated by high-opacity lanthanide-rich ejecta, suggesting nucleosynthesis to the third r-process peak (atomic masses a≈ 195). this discovery confirms that neutron-star mergers produce kilo-/macronovae and that they are at least a major—if not the dominant—site of rapid neutron capture nucleosynthesis in the universe. | the emergence of a lanthanide-rich kilonova following the merger of two neutron stars |
a new piece of evidence supporting the photoevaporation-driven evolution model for low-mass, close-in exoplanets was recently presented by the california-kepler survey. the radius distribution of the kepler planets is shown to be bimodal, with a “valley” separating two peaks at 1.3 and 2.6 r ⊕. such an “evaporation valley” had been predicted by numerical models previously. here, we develop a minimal model to demonstrate that this valley results from the following fact: the timescale for envelope erosion is the longest for those planets with hydrogen/helium-rich envelopes that, while only a few percent in weight, double its radius. the timescale falls for envelopes lighter than this because the planet’s radius remains largely constant for tenuous envelopes. the timescale also drops for heavier envelopes because the planet swells up faster than the addition of envelope mass. photoevaporation therefore herds planets into either bare cores (∼1.3 r ⊕), or those with double the core’s radius (∼2.6 r ⊕). this process mostly occurs during the first 100 myr when the stars’ high-energy fluxes are high and nearly constant. the observed radius distribution further requires the kepler planets to be clustered around 3 m ⊕ in mass, born with h/he envelopes more than a few percent in mass, and that their cores are similar to the earth in composition. such envelopes must have been accreted before the dispersal of the gas disks, while the core composition indicates formation inside the ice line. lastly, the photoevaporation model fails to account for bare planets beyond ∼30-60 days; if these planets are abundant, they may point to a significant second channel for planet formation, resembling the solar system terrestrial planets. | the evaporation valley in the kepler planets |
i introduce batman, a python package for modeling exoplanet transit light curves. the batman package supports calculation of light curves for any radially symmetric stellar limb darkening law, using a new integration algorithm for models that cannot be quickly calculated analytically. the code uses c extension modules to speed up model calculation and is parallelized with openmp. for a typical light curve with 100 data points in transit, batman can calculate one million quadratic limb-darkened models in 30 seconds with a single 1.7 ghz intel core i5 processor. the same calculation takes seven minutes using the four-parameter nonlinear limb darkening model (computed to 1 ppm accuracy). maximum truncation error for integrated models is an input parameter that can be set as low as 0.001 ppm, ensuring that the community is prepared for the precise transit light curves we anticipate measuring with upcoming facilities. the batman package is open source and publicly available at https://github.com/lkreidberg/batman . | batman: basic transit model calculation in python |
the lowest luminosity (l < 105l⊙) milky way satellite galaxies represent the extreme lower limit of the galaxy luminosity function. these ultra-faint dwarfs are the oldest, most dark matter-dominated, most metal-poor, and least chemically evolved stellar systems known. they therefore provide unique windows into the formation of the first galaxies and the behavior of dark matter on small scales. in this review, we summarize the discovery of ultra-faint dwarfs in the sloan digital sky survey in 2005 and the subsequent observational and theoretical progress in understanding their nature and origin. we describe their stellar kinematics, chemical abundance patterns, structural properties, stellar populations, orbits, and luminosity function, as well as what can be learned from each type of measurement. we conclude the following: in most cases, the stellar velocity dispersions of ultra-faint dwarfs are robust against systematic uncertainties such as binary stars and foreground contamination. the chemical abundance patterns of stars in ultra-faint dwarfs require two sources of r-process elements, one of which can likely be attributed to neutron star mergers. even under conservative assumptions, only a small fraction of ultra-faint dwarfs may have suffered significant tidal stripping of their stellar components. determining the properties of the faintest dwarfs out to the virial radius of the milky way will require very large investments of observing time with future telescopes.finally, we offer a look forward at the observations that will be possible with future facilities as the push toward a complete census of the local group dwarf galaxy population continues. | the faintest dwarf galaxies |
context. young circumstellar disks are the birthplaces of planets. their study is of prime interest to understand the physical and chemical conditions under which planet formation takes place. only very few detections of planet candidates within these disks exist, and most of them are currently suspected to be disk features.aims: in this context, the transition disk around the young star pds 70 is of particular interest, due to its large gap identified in previous observations, indicative of ongoing planet formation. we aim to search for the presence of an embedded young planet and search for disk structures that may be the result of disk-planet interactions and other evolutionary processes.methods: we analyse new and archival near-infrared images of the transition disk pds 70 obtained with the vlt/sphere, vlt/naco, and gemini/nici instruments in polarimetric differential imaging and angular differential imaging modes.results: we detect a point source within the gap of the disk at about 195 mas ( 22 au) projected separation. the detection is confirmed at five different epochs, in three filter bands and using different instruments. the astrometry results in an object of bound nature, with high significance. the comparison of the measured magnitudes and colours to evolutionary tracks suggests that the detection is a companion of planetary mass. the luminosity of the detected object is consistent with that of an l-type dwarf, but its ir colours are redder, possibly indicating the presence of warm surrounding material. further, we confirm the detection of a large gap of 54 au in size within the disk in our scattered light images, and detect a signal from an inner disk component. we find that its spatial extent is very likely smaller than 17 au in radius, and its position angle is consistent with that of the outer disk. the images of the outer disk show evidence of a complex azimuthal brightness distribution which is different at different wavelengths and may in part be explained by rayleigh scattering from very small grains.conclusions: the detection of a young protoplanet within the gap of the transition disk around pds 70 opens the door to a so far observationally unexplored parameter space of planetary formation and evolution. future observations of this system at different wavelengths and continuing astrometry will allow us to test theoretical predictions regarding planet-disk interactions, planetary atmospheres, and evolutionary models. based on observations performed with eso telescopes at the paranal observatory under programmes 095.c-0298, 095.c-0404, 096.c-0333, 097.c-0206, 097.c-1001, and 099.c-0891.the reduced images and datacubes are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/617/a44 | discovery of a planetary-mass companion within the gap of the transition disk around pds 70 |
we consider quarkyonic matter to naturally explain the observed properties of neutron stars. we argue that such matter might exist at densities close to that of nuclear matter, and at the onset, the pressure and the sound velocity in quarkyonic matter increase rapidly. in the limit of large number of quark colors nc, this transition is characterized by a discontinuous change in pressure as a function of baryon number density. we make a simple model of quarkyonic matter and show that generically the sound velocity is a nonmonotonic function of density—it reaches a maximum at relatively low density, decreases, and then increases again to its asymptotic value of 1 /√{3 }. | quarkyonic matter and neutron stars |
recent rapid progress in neutron-star (ns) observations offers great potential to constrain the properties of strongly interacting matter under the most extreme conditions. in order to fully exploit the current observational inputs and to study the impact of future observations of ns masses, radii, and tidal deformabilities, we analyze a large ensemble of randomly generated viable ns-matter equations of state (eoss) and the corresponding rotating stellar structures. we discuss the compatibility and impact of various hypotheses and measurements on the eos, including those involving the merger product of the gravitational-wave (gw) event gw170817, the binary-merger components in gw190814, and radius measurements of the pulsar psr j 0740 +6620 . we obtain an upper limit for the dimensionless spin of a rigidly rotating ns |χ | <0.81 , an upper limit for the compactness of a ns g m /(r c2)<0.33 , and find that the conservative hypothesis that the remnant in gw170817 ultimately collapsed to a black hole strongly constrains the eos and the maximal mass of nss, implying mtov<2.53 m⊙ (or mtov<2.19 m⊙ if we assume that a hypermassive ns was created). additionally, we derive a novel lower limit for the tidal deformability as a function of the ns mass and provide fitting formulas that can be used to set priors for parameter estimation and to discern whether neutron stars or other compact objects are involved in future low-mass gw events. finally, we find that the recent nicer results for the radius of the massive ns psr j 0740 +6620 place strong constraints for the behavior of the eos and that the indicated radius values r (2 m⊙)≳11 km are compatible with moderate speeds of sound in ns matter and thus with the existence of quark-matter cores in massive nss. | multimessenger constraints for ultradense matter |
using a heavy-mass effective field theory (heft), we study gravitational-wave emission in the scattering of two spinless black holes or neutron stars of arbitrary masses at next-to-leading order in the post-minkowskian expansion. we compute the contributions to the one-loop scattering amplitude with four scalars and one graviton which are relevant to the calculation of the waveforms, also presenting expressions of classical tree-level amplitudes with four scalars and up to two radiated gravitons. the latter are obtained using a novel on-shell recursion relation for classical amplitudes with four scalars and an arbitrary number of gravitons. our one-loop five-point amplitude is expressed in terms of a single family of master integrals with the principal value prescription for linearised massive propagators, which we evaluate using differential equations. in our heft approach, soft/heavy-mass expansions of complete integrands are avoided, and all hyper-classical iterations and quantum corrections are dropped at the diagrammatic level, thereby computing directly contributions to classical physics. our result exhibits the expected factorisation of infrared divergences, the correct soft limits, and highly nontrivial cancellations of spurious poles. finally, using our amplitude result we compute numerically the corresponding next-to-leading corrections to the spectral waveforms and the far-field time-domain waveforms using the newman-penrose scalar ψ4. | one-loop gravitational bremsstrahlung and waveforms from a heavy-mass effective field theory |
the james webb space telescope is now detecting early black holes (bhs) as they transition from "seeds" to supermassive bhs. recently, bogdan et al. reported the detection of an x-ray luminous supermassive bh, uhz-1, with a photometric redshift at z > 10. such an extreme source at this very high redshift provides new insights on seeding and growth models for bhs given the short time available for formation and growth. harnessing the exquisite sensitivity of jwst/nirspec, here we report the spectroscopic confirmation of uhz-1 at z = 10.073 ± 0.002. we find that the nirspec/prism spectrum is typical of recently discovered z ≈ 10 galaxies, characterized primarily by star formation features. we see no clear evidence of the powerful x-ray source in the rest-frame uv/optical spectrum, which may suggest heavy obscuration of the central bh, in line with the compton-thick column density measured in the x-rays. we perform a stellar population fit simultaneously to the new nirspec spectroscopy and previously available photometry. the fit yields a stellar-mass estimate for the host galaxy that is significantly better constrained than prior photometric estimates ( ${m}_{\star }\sim {1.4}_{-0.4}^{+0.3}\times {10}^{8}$ m ⊙). given the predicted bh mass (m bh ~ 107-108 m ⊙), the resulting ratio of m bh/m ⋆ remains 2 to 3 orders of magnitude higher than local values, thus lending support to the heavy seeding channel for the formation of supermassive bhs within the first billion years of cosmic evolution. | uncover: the growth of the first massive black holes from jwst/nirspec-spectroscopic redshift confirmation of an x-ray luminous agn at z = 10.1 |
we provide a comprehensive review of major developments in our understanding of gamma-ray bursts, with particular focus on the discoveries made within the last fifteen years when their true nature was uncovered. we describe the observational properties of photons from the radio to 100s gev bands, both in the prompt emission and the afterglow phases. mechanisms for the generation of these photons in grbs are discussed and confronted with observations to shed light on the physical properties of these explosions, their progenitor stars and the surrounding medium. after presenting observational evidence that a powerful, collimated, jet moving at close to the speed of light is produced in these explosions, we describe our current understanding regarding the generation, acceleration, and dissipation of the jet. we discuss mounting observational evidence that long duration grbs are produced when massive stars die, and that at least some short duration bursts are associated with old, roughly solar mass, compact stars. the question of whether a black-hole or a strongly magnetized, rapidly rotating neutron star is produced in these explosions is also discussed. we provide a brief summary of what we have learned about relativistic collisionless shocks and particle acceleration from grb afterglow studies, and discuss the current understanding of radiation mechanism during the prompt emission phase. we discuss theoretical predictions of possible high-energy neutrino emission from grbs and the current observational constraints. finally, we discuss how these explosions may be used to study cosmology, e.g. star formation, metal enrichment, reionization history, as well as the formation of first stars and galaxies in the universe. | the physics of gamma-ray bursts & relativistic jets |
gravitational waves provide a unique tool for observational astronomy. while the first ligo-virgo catalogue of gravitational-wave transients (gwtc-1) contains 11 signals from black hole and neutron star binaries, the number of observations is increasing rapidly as detector sensitivity improves. to extract information from the observed signals, it is imperative to have fast, flexible, and scalable inference techniques. in a previous paper, we introduced bilby: a modular and user-friendly bayesian inference library adapted to address the needs of gravitational-wave inference. in this work, we demonstrate that bilby produces reliable results for simulated gravitational-wave signals from compact binary mergers, and verify that it accurately reproduces results reported for the 11 gwtc-1 signals. additionally, we provide configuration and output files for all analyses to allow for easy reproduction, modification, and future use. this work establishes that bilby is primed and ready to analyse the rapidly growing population of compact binary coalescence gravitational-wave signals. | bayesian inference for compact binary coalescences with bilby: validation and application to the first ligo-virgo gravitational-wave transient catalogue |
we present the next generation public exoplanet fitting software, exofastv2. it is capable of fitting an arbitrary number of planets, radial velocity data sets, astrometric data sets, and/or transits observed with any combination of wavelengths. we model the star simultaneously in the fit and provide several state-of-the-art ways to constrain its properties, including taking advantage of the now-ubiquitous all-sky catalog photometry and gaia parallaxes. exofastv2 can model the star by itself, too. multi-planet systems are modeled self-consistently with the same underlying stellar mass that defines their semi-major axes through kepler's law and the planetary period. transit timing, duration, and depth variations can be modeled with a simple command line option. we explain our methodology and rationale as well as provide an improved version of the core transit model that is both 25\% faster and more accurate. we highlight several potential pitfalls in exoplanet modeling, including the handling of eccentricity in transit-only fits, that the standard exoplanet convention for $\omega$ uses a left-handed coordinate system, contrary to most modern textbooks, how to avoid an important degeneracy when allowing negative companion masses, and a widely unappreciated, potential 10-minute ambiguity in the reported transit times. exofastv2 is available at https://github.com/jdeast/exofastv2 . the code is written in idl, and includes an executable that can be run freely and legally without an idl license or any knowledge of the language. extensive documentation and tutorials are included in the distribution for a variety of example fits. advanced amateurs and undergrads have successfully performed sophisticated global fits of complex planetary systems with exofastv2. it is therefore a powerful tool for education and outreach as well as the broader professional community. | exofastv2: a public, generalized, publication-quality exoplanet modeling code |
picture yourself in the wave zone of a gravitational scattering event of two massive, spinning compact bodies (black holes, neutron stars or stars). we show that this system of genuine astrophysical interest enjoys a hidden n = 2 supersymmetry, at least to the order of spin-squared (quadrupole) interactions in arbitrary d spacetime dimensions. using the n = 2 supersymmetric worldline action, augmented by finite-size corrections for the non-kerr black hole case, we build a quadratic-in-spin extension to the worldline quantum field theory (wqft) formalism introduced in our previous work, and calculate the two bodies' deflection and spin kick to sub-leading order in the post-minkowskian expansion in newton's constant g. for spins aligned to the normal vector of the scattering plane we also obtain the scattering angle. all d-dimensional observables are derived from an eikonal phase given as the free energy of the wqft that is invariant under the n = 2 supersymmetry transformations. | susy in the sky with gravitons |
in the era of precision cosmology, it is essential to determine the hubble constant empirically with an accuracy of one per cent or better1. at present, the uncertainty on this constant is dominated by the uncertainty in the calibration of the cepheid period-luminosity relationship2,3 (also known as the leavitt law). the large magellanic cloud has traditionally served as the best galaxy with which to calibrate cepheid period-luminosity relations, and as a result has become the best anchor point for the cosmic distance scale4,5. eclipsing binary systems composed of late-type stars offer the most precise and accurate way to measure the distance to the large magellanic cloud. currently the limit of the precision attainable with this technique is about two per cent, and is set by the precision of the existing calibrations of the surface brightness-colour relation5,6. here we report a calibration of the surface brightness-colour relation with a precision of 0.8 per cent. we use this calibration to determine a geometrical distance to the large magellanic cloud that is precise to 1 per cent based on 20 eclipsing binary systems. the final distance is 49.59 ± 0.09 (statistical) ± 0.54 (systematic) kiloparsecs. | a distance to the large magellanic cloud that is precise to one per cent |
we analyse the chemical properties of three z~ 8 galaxies behind the galaxy cluster smacs j0723.3-7327, observed as part of the early release observations programme of the james webb space telescope. exploiting [o iii]λ4363 auroral line detections in nirspec spectra, we robustly apply the direct te method for the very first time at such high redshift, measuring metallicities ranging from extremely metal poor (12 + log(o/h)≈ 7) to about one-third solar. we also discuss the excitation properties of these sources, and compare them with local strong-line metallicity calibrations. we find that none of the considered diagnostics match simultaneously the observed relations between metallicity and strong-line ratios for the three sources, implying that a proper re-assessment of the calibrations may be needed at these redshifts. on the mass-metallicity plane, the two galaxies at z ~ 7.6 ($\rm log(m_*/m_{\odot }) = 8.1, 8.7$) have metallicities that are consistent with the extrapolation of the mass-metallicity relation at z~2-3, while the least massive galaxy at z ~ 8.5 ($\rm log(m_*/m_{\odot }) = 7.8$) shows instead a significantly lower metallicity. the three galaxies show different level of offset relative to the fundamental metallicity relation, with two of them (at z~ 7.6) being marginally consistent, while the z~ 8.5 source deviating significantly, being probably far from the smooth equilibrium between gas flows, star formation, and metal enrichment in place at later epochs. | the chemical enrichment in the early universe as probed by jwst via direct metallicity measurements at z ∼ 8 |
constraints set on key parameters of the nuclear matter equation of state (eos) by the values of the tidal deformability, inferred from gw170817, are examined by using a diverse set of relativistic and nonrelativistic mean-field models. these models are consistent with bulk properties of finite nuclei as well as with the observed lower bound on the maximum mass of neutron star ≈2 m⊙ . the tidal deformability shows a strong correlation with specific linear combinations of the isoscalar and isovector nuclear matter parameters associated with the eos. such correlations suggest that a precise value of the tidal deformability can put tight bounds on several eos parameters, in particular on the slope of the incompressibility and the curvature of the symmetry energy. the tidal deformability obtained from the gw170817 and its uv, optical and infrared counterpart sets the radius of a canonical 1.4 m⊙ neutron star to be 11.82 ≤r1.4≤13.72 km . | gw170817: constraining the nuclear matter equation of state from the neutron star tidal deformability |
the spectral analysis and data products in data release 16 (dr16; 2019 december) from the high-resolution near-infrared apache point observatory galactic evolution experiment (apogee)-2/sloan digital sky survey (sdss)-iv survey are described. compared to the previous apogee data release (dr14; 2017 july), apogee dr16 includes about 200,000 new stellar spectra, of which 100,000 are from a new southern apogee instrument mounted on the 2.5 m du pont telescope at las campanas observatory in chile. dr16 includes all data taken up to 2018 august, including data released in previous data releases. all of the data have been re-reduced and re-analyzed using the latest pipelines, resulting in a total of 473,307 spectra of 437,445 stars. changes to the analysis methods for this release include, but are not limited to, the use of marcs model atmospheres for calculation of the entire main grid of synthetic spectra used in the analysis, a new method for filling "holes" in the grids due to unconverged model atmospheres, and a new scheme for continuum normalization. abundances of the neutron-capture element ce are included for the first time. a new scheme for estimating uncertainties of the derived quantities using stars with multiple observations has been applied, and calibrated values of surface gravities for dwarf stars are now supplied. compared to dr14, the radial velocities derived for this release more closely match those in the gaia dr2 database, and a clear improvement in the spectral analysis of the coolest giants can be seen. the reduced spectra as well as the result of the analysis can be downloaded using links provided on the sdss dr16 web page. | apogee data and spectral analysis from sdss data release 16: seven years of observations including first results from apogee-south |
we present jwst/nirspec prism spectroscopy of seven galaxies selected from cosmic evolution early release science (ceers) survey nircam imaging with photometric redshifts z phot > 8. we measure emission line redshifts of z = 7.65 and 8.64 for two galaxies. for two other sources without securely detected emission lines we measure $z={9.77}_{-0.29}^{+0.37}$ and ${10.01}_{-0.19}^{+0.14}$ by fitting model spectral templates to the prism data, from which we detect continuum breaks consistent with lyα opacity from a mostly neutral intergalactic medium. the presence of strong breaks and the absence of strong emission lines give high confidence that these two galaxies have redshifts z > 9.6, but the redshift values derived from the breaks alone have large uncertainties given the low spectral resolution and relatively low s/n of the ceers nirspec prism data. the two z ~ 10 sources observed are relatively luminous (m uv < -20), with blue continua (-2.3 ≲ β ≲ -1.9) and low dust attenuation ( ${a}_{v}\simeq {0.15}_{-0.1}^{+0.3}$ ); and at least one of them has a high stellar mass for a galaxy at that redshift ( $\mathrm{log}({m}_{\star }/{m}_{\odot })\simeq {9.3}_{-0.3}^{+0.2}$ ). considered together with spectroscopic observations of other ceers nircam-selected high-z galaxy candidates in the literature, we find a high rate of redshift confirmation and low rate of confirmed interlopers (8%). ten out of 35 z > 8 candidates with ceers nirspec spectroscopy do not have secure redshifts, but the absence of emission lines in their spectra is consistent with redshifts z > 9.6. we find that z > 8 photometric redshifts are generally in agreement (within their uncertainties) with the spectroscopic values, but also that the photometric redshifts tend to be slightly overestimated (<δz> = 0.45 ± 0.11), suggesting that current templates do not fully describe the spectra of very-high-z sources. overall, the spectroscopy solidifies photometric redshift evidence for a high spatial density of bright galaxies at z > 8 compared to theoretical model predictions, and further disfavors an accelerated decline in the integrated uv luminosity density at z > 8. | spectroscopic confirmation of ceers nircam-selected galaxies at z ≃ 8-10 |
context. the gaia dr3 catalogue contains, for the first time, about 800 000 solutions with either orbital elements or trend parameters for astrometric, spectroscopic, and eclipsing binaries, and combinations of these three.aims: with this paper, we aim to illustrate the huge potential of this large non-single-star catalogue.methods: using the orbital solutions and models of the binaries, we have built a catalogue of tens of thousands of stellar masses or lower limits thereof, some with consistent flux ratios. properties concerning the completeness of the binary catalogues are discussed, statistical features of the orbital elements are explained, and a comparison with other catalogues is performed.results: illustrative applications are proposed for binaries across the hertzsprung-russell diagram (hrd). binarity is studied in the giant branch and a search for genuine spectroscopic binaries among long-period variables is performed. the discovery of new el cvn systems illustrates the potential of combining variability and binarity catalogues. potential compact object companions are presented, mainly white dwarf companions or double degenerates, but one candidate neutron star is also found. towards the bottom of the main sequence, the orbits of previously suspected binary ultracool dwarfs are determined and new candidate binaries are discovered. the long awaited contribution of gaia to the analysis of the substellar regime shows the brown dwarf desert around solar-type stars using true rather than minimum masses, and provides new important constraints on the occurrence rates of substellar companions to m dwarfs. several dozen new exoplanets are proposed, including two with validated orbital solutions and one super-jupiter orbiting a white dwarf, all being candidates requiring confirmation. besides binarity, higher order multiple systems are also found.conclusions: by increasing the number of known binary orbits by more than one order of magnitude, gaia dr3 will provide a rich reservoir of dynamical masses and an important contribution to the analysis of stellar multiplicity. | gaia data release 3. stellar multiplicity, a teaser for the hidden treasure |
the habitable exoplanet observatory, or habex, has been designed to be the great observatory of the 2030s. for the first time in human history, technologies have matured sufficiently to enable an affordable space-based telescope mission capable of discovering and characterizing earthlike planets orbiting nearby bright sunlike stars in order to search for signs of habitability and biosignatures. such a mission can also be equipped with instrumentation that will enable broad and exciting general astrophysics and planetary science not possible from current or planned facilities. habex is a space telescope with unique imaging and multi-object spectroscopic capabilities at wavelengths ranging from ultraviolet (uv) to near-ir. these capabilities allow for a broad suite of compelling science that cuts across the entire nasa astrophysics portfolio. habex has three primary science goals: (1) seek out nearby worlds and explore their habitability; (2) map out nearby planetary systems and understand the diversity of the worlds they contain; (3) enable new explorations of astrophysical systems from our own solar system to external galaxies by extending our reach in the uv through near-ir. this great observatory science will be selected through a competed go program, and will account for about 50% of the habex primary mission. the preferred habex architecture is a 4m, monolithic, off-axis telescope that is diffraction-limited at 0.4 microns and is in an l2 orbit. habex employs two starlight suppression systems: a coronagraph and a starshade, each with their own dedicated instrument. | the habitable exoplanet observatory (habex) mission concept study final report |
the hyper suprime-cam subaru strategic program (hsc-ssp) is a three-layered imaging survey aimed at addressing some of the most important outstanding questions in astronomy today, including the nature of dark matter and dark energy. the survey has been awarded 300 nights of observing time at the subaru telescope, and it started in 2014 march. this paper presents the first public data release of hsc-ssp. this release includes data taken in the first 1.7 yr of observations (61.5 nights), and each of the wide, deep, and ultradeep layers covers about 108, 26, and 4 square degrees down to depths of i ∼ 26.4, ∼26.5, and ∼27.0 mag, respectively (5 σ for point sources). all the layers are observed in five broad bands (grizy), and the deep and ultradeep layers are observed in narrow bands as well. we achieve an impressive image quality of 0{^''.}6 in the i band in the wide layer. we show that we achieve 1%-2% point spread function (psf) photometry (root mean square) both internally and externally (against pan-starrs1), and ∼10 mas and 40 mas internal and external astrometric accuracy, respectively. both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers. in addition to the pipeline products, we also provide value-added products such as photometric redshifts and a collection of public spectroscopic redshifts. detailed descriptions of all the data can be found online. the data release website is https://hsc-release.mtk.nao.ac.jp. | first data release of the hyper suprime-cam subaru strategic program |
we present high-precision timing data over time spans of up to 11 years for 45 millisecond pulsars observed as part of the north american nanohertz observatory for gravitational waves (nanograv) project, aimed at detecting and characterizing low-frequency gravitational waves. the pulsars were observed with the arecibo observatory and/or the green bank telescope at frequencies ranging from 327 mhz to 2.3 ghz. most pulsars were observed with approximately monthly cadence, and six high-timing-precision pulsars were observed weekly. all were observed at widely separated frequencies at each observing epoch in order to fit for time-variable dispersion delays. we describe our methods for data processing, time-of-arrival (toa) calculation, and the implementation of a new, automated method for removing outlier toas. we fit a timing model for each pulsar that includes spin, astrometric, and (for binary pulsars) orbital parameters; time-variable dispersion delays; and parameters that quantify pulse-profile evolution with frequency. the timing solutions provide three new parallax measurements, two new shapiro delay measurements, and two new measurements of significant orbital-period variations. we fit models that characterize sources of noise for each pulsar. we find that 11 pulsars show significant red noise, with generally smaller spectral indices than typically measured for non-recycled pulsars, possibly suggesting a different origin. a companion paper uses these data to constrain the strength of the gravitational-wave background. | the nanograv 11-year data set: high-precision timing of 45 millisecond pulsars |
the astrophysical rapid neutron capture process or ' r process' of nucleosynthesis is believed to be responsible for the production of approximately half the heavy element abundances found in nature. this multifaceted problem remains one of the greatest open challenges in all of physics. knowledge of nuclear physics properties such as masses, β-decay and neutron capture rates, as well as β-delayed neutron emission probabilities are critical inputs that go into calculations of r-process nucleosynthesis. while properties of nuclei near stability have been established, much still remains unknown regarding neutron-rich nuclei far from stability that may participate in the r process. sensitivity studies gauge the astrophysical response of a change in nuclear physics input(s) which allows for the isolation of the most important nuclear properties that shape the final abundances observed in nature. this review summarizes the extent of recent sensitivity studies and highlights how these studies play a key role in facilitating new insight into the r process. the development of these tools promotes a focused effort for state-of-the-art measurements, motivates construction of new facilities and will ultimately move the community toward addressing the grand challenge of 'how were the elements from iron to uranium made?'. | the impact of individual nuclear properties on r-process nucleosynthesis |
we present the details of the photometric and astrometric calibration of the pan-starrs1 3π survey. the photometric goals were to reduce the systematic effects introduced by the camera and detectors, and to place all of the observations onto a photometric system with consistent zero-points over the entire area surveyed, the ≈30,000 deg2 north of δ = -30°. using external comparisons, we demonstrate that the resulting photometric system is consistent across the sky to between 7 and 12.4 mmag depending on the filter. for bright stars, the systematic error floor for individual measurements is (σg, σr, σi, σz, σy) = (14, 14, 15, 15, 18) mmag. the astrometric calibration compensates for similar systematic effects so that positions, proper motions, and parallaxes are reliable as well. the bright-star systematic error floor for individual astrometric measurements is 16 mas. the pan-starrs data release 2 (dr2) astrometric system is tied to the gaia dr1 coordinate frame with a systematic uncertainty of ∼5 mas. | pan-starrs photometric and astrometric calibration |
we introduce a new, powerful method to constrain properties of neutron stars (nss). we show that the total mass of gw170817 provides a reliable constraint on the stellar radius if the merger did not result in a prompt collapse as suggested by the interpretation of associated electromagnetic emission. the radius {r}1.6 of nonrotating nss with a mass of 1.6 {m}⊙can be constrained to be larger than {10.68}-0.04+0.15 km, and the radius r max of the nonrotating maximum-mass configuration must be larger than {9.60}-0.03+0.14 km. we point out that detections of future events will further improve these constraints. moreover, we show that a future event with a signature of a prompt collapse of the merger remnant will establish even stronger constraints on the ns radius from above and the maximum mass m max of nss from above. these constraints are particularly robust because they only require a measurement of the chirp mass and a distinction between prompt and delayed collapse of the merger remnant, which may be inferred from the electromagnetic signal or even from the presence/absence of a ringdown gravitational-wave (gw) signal. this prospect strengthens the case of our novel method of constraining ns properties, which is directly applicable to future gw events with accompanying electromagnetic counterpart observations. we emphasize that this procedure is a new way of constraining ns radii from gw detections independent of existing efforts to infer radius information from the late inspiral phase or post-merger oscillations, and it does not require particularly loud gw events. | neutron-star radius constraints from gw170817 and future detections |
the advanced ligo and advanced virgo gravitational-wave (gw) detectors will begin operation in the coming years, with compact binary coalescence events a likely source for the first detections. the gravitational waveforms emitted directly encode information about the sources, including the masses and spins of the compact objects. recovering the physical parameters of the sources from the gw observations is a key analysis task. this work describes the lalinference software library for bayesian parameter estimation of compact binary signals, which builds on several previous methods to provide a well-tested toolkit which has already been used for several studies. we show that our implementation is able to correctly recover the parameters of compact binary signals from simulated data from the advanced gw detectors. we demonstrate this with a detailed comparison on three compact binary systems: a binary neutron star, a neutron star-black hole binary and a binary black hole, where we show a cross comparison of results obtained using three independent sampling algorithms. these systems were analyzed with nonspinning, aligned spin and generic spin configurations respectively, showing that consistent results can be obtained even with the full 15-dimensional parameter space of the generic spin configurations. we also demonstrate statistically that the bayesian credible intervals we recover correspond to frequentist confidence intervals under correct prior assumptions by analyzing a set of 100 signals drawn from the prior. we discuss the computational cost of these algorithms, and describe the general and problem-specific sampling techniques we have used to improve the efficiency of sampling the compact binary coalescence parameter space. | parameter estimation for compact binaries with ground-based gravitational-wave observations using the lalinference software library |
context. the large astrometric and photometric survey performed by the gaia mission allows for a panoptic view of the galactic disc and its stellar cluster population. hundreds of stellar clusters were only discovered after the latest gaia data release (dr2) and have yet to be characterised.aims: here we make use of the deep and homogeneous gaia photometry down to g = 18 to estimate the distance, age, and interstellar reddening for about 2000 stellar clusters identified with gaia dr2 astrometry. we use these objects to study the structure and evolution of the galactic disc.methods: we relied on a set of objects with well-determined parameters in the literature to train an artificial neural network to estimate parameters from the gaia photometry of cluster members and their mean parallax.results: we obtain reliable parameters for 1867 clusters. our catalogue confirms the relative lack of old stellar clusters in the inner disc (with a few notable exceptions). we also quantify and discuss the variation of scale height with cluster age, and we detect the galactic warp in the distribution of old clusters.conclusions: this work results in a large and homogeneous cluster catalogue, allowing one to trace the structure of the disc out to distances of ∼4 kpc. however, the present sample is still unable to trace the outer spiral arm of the milky way, which indicates that the outer disc cluster census might still be incomplete. list of cluster parameters and complete list of their members are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/640/a1 | painting a portrait of the galactic disc with its stellar clusters |
the discovery of the gravitational-wave (gw) source gw150914 with the advanced ligo detectors provides the first observational evidence for the existence of binary black hole (bh) systems that inspiral and merge within the age of the universe. such bh mergers have been predicted in two main types of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. the measured masses robustly demonstrate that relatively “heavy” bhs (≳ 25 {m}⊙ ) can form in nature. this discovery implies relatively weak massive-star winds and thus the formation of gw150914 in an environment with a metallicity lower than about 1/2 of the solar value. the rate of binary-bh (bbh) mergers inferred from the observation of gw150914 is consistent with the higher end of rate predictions (≳ 1 gpc-3 yr-1) from both types of formation models. the low measured redshift (z≃ 0.1) of gw150914 and the low inferred metallicity of the stellar progenitor imply either bbh formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several gyr. this discovery motivates further studies of binary-bh formation astrophysics. it also has implications for future detections and studies by advanced ligo and advanced virgo, and gw detectors in space. | astrophysical implications of the binary black-hole merger gw150914 |
we explore the orbital implications of the supermassive black hole (smbh) binary in ugc4211, for the frequency spectrum of stochastic gravitational wave background (sgwb) being measured with pulsar timing arrays. the smbh binary in ugc4211 has a projected separation of $\sim 230$ pc and relative velocity of $\sim 150$ km/s along the line of sight. it orbits a common disk of gas and stars, with a total dynamical mass of $\sim 10^9 m_\odot$ which is several times larger than the combined smbhs plus the observed gas and stars. this can be explained by a massive soliton of wave dark matter present within the orbit of two smbhs. such a scenario is encouraging as during galaxy merger, the two precursor galactic solitons are expected to combine to generate a new soliton and hence the two initial smbhs become efficiently bound. generalizing this scenario to the cosmological population of smbh binaries, we show that the sgwb spectrum produced by their late-stage inspiraling is modified preferentially at low frequency by the presence of the soliton. finally we discuss future prospects for this proof-of-concept study, by fitting this scenario to the 15-year nanograv data. | binary supermassive black holes orbiting dark matter solitons: from the dual agn in ugc4211 to nanohertz gravitational waves |
the next generation of ground-based gravitational-wave detectors will observe coalescences of black holes and neutron stars throughout the cosmos, thousands of them with exceptional fidelity. the science book is the result of a 3-year effort to study the science capabilities of networks of next generation detectors. such networks would make it possible to address unsolved problems in numerous areas of physics and astronomy, from cosmology to beyond the standard model of particle physics, and how they could provide insights into workings of strongly gravitating systems, astrophysics of compact objects and the nature of dense matter. it is inevitable that observatories of such depth and finesse will make new discoveries inaccessible to other windows of observation. in addition to laying out the rich science potential of the next generation of detectors, this report provides specific science targets in five different areas in physics and astronomy and the sensitivity requirements to accomplish those science goals. this report is the second in a six part series of reports by the gwic 3g subcommittee: i) expanding the reach of gravitational wave observatories to the edge of the universe, ii) the next generation global gravitational wave observatory: the science book (this report), iii) 3g r&d: r&d for the next generation of ground-based gravitational wave detectors, iv) gravitational wave data analysis: computing challenges in the 3g era, v) future ground-based gravitational-wave observatories: synergies with other scientific communities, and vi) an exploration of possible governance models for the future global gravitational-wave observatory network. | the next generation global gravitational wave observatory: the science book |
the dominant decay mode of atomic nuclei is beta decay (β-decay), a process that changes a neutron into a proton (and vice versa). this decay offers a window to physics beyond the standard model, and is at the heart of microphysical processes in stellar explosions and element synthesis in the universe1-3. however, observed β-decay rates in nuclei have been found to be systematically smaller than for free neutrons: this 50-year-old puzzle about the apparent quenching of the fundamental coupling constant by a factor of about 0.75 (ref. 4) is without a first-principles theoretical explanation. here, we demonstrate that this quenching arises to a large extent from the coupling of the weak force to two nucleons as well as from strong correlations in the nucleus. we present state-of-the-art computations of β-decays from light- and medium-mass nuclei to 100sn by combining effective field theories of the strong and weak forces5 with powerful quantum many-body techniques6-8. our results are consistent with experimental data and have implications for heavy element synthesis in neutron star mergers9-11 and predictions for the neutrino-less double-β-decay3, where an analogous quenching puzzle is a source of uncertainty in extracting the neutrino mass scale12. | discrepancy between experimental and theoretical β-decay rates resolved from first principles |
we present both the technical overview and main science drivers of the fourth phase of the optical gravitational lensing experiment (hereafter ogle-iv). ogle-iv is currently one of the largest sky variability surveys worldwide, targeting the densest stellar regions of the sky. the survey covers over 3000 square degrees in the sky and monitors regularly over a billion sources. the main targets include the inner galactic bulge and the magellanic system. their photometry spans the range of 12<i<21 mag and 13<i<21.7 mag, respectively. supplementary shallower galaxy variability survey covers the extended galactic bulge and 2/3 of the whole galactic disk within the magnitude range of 10<i<19 mag. all ogle-iv surveys provide photometry with milli-magnitude accuracy at the bright end. the cadence of observations varies from 19-60 minutes in the inner galactic bulge to 1-3 days in the remaining galactic bulge fields, magellanic system and the galactic disk. ogle-iv provides the astronomical community with a number of real time services. the early warning system (ews) contains information on two thousand gravitational microlensing events being discovered in real time annually, the ogle transient detection system (otds) delivers over 200 supernovae a year. we also provide the real time photometry of unpredictable variables such as optical counterparts to the x-ray sources and r coronae borealis stars. hundreds of thousands new variable stars have already been discovered and classified by the ogle survey. the number of new detections will be at least doubled during the current ogle-iv phase. the survey was designed and optimized primarily to conduct the second generation microlensing survey for exoplanets. it has already contributed significantly to the increase of the discovery rate of microlensing exoplanets and free-floating planets. | ogle-iv: fourth phase of the optical gravitational lensing experiment |
context. espresso is the new high-resolution spectrograph of eso's very large telescope (vlt). it was designed for ultra-high radial-velocity (rv) precision and extreme spectral fidelity with the aim of performing exoplanet research and fundamental astrophysical experiments with unprecedented precision and accuracy. it is able to observe with any of the four unit telescopes (uts) of the vlt at a spectral resolving power of 140 000 or 190 000 over the 378.2 to 788.7 nm wavelength range; it can also observe with all four uts together, turning the vlt into a 16 m diameter equivalent telescope in terms of collecting area while still providing a resolving power of 70 000.aims: we provide a general description of the espresso instrument, report on its on-sky performance, and present our guaranteed time observation (gto) program along with its first results.methods: espresso was installed on the paranal observatory in fall 2017. commissioning (on-sky testing) was conducted between december 2017 and september 2018. the instrument saw its official start of operations on october 1, 2018, but improvements to the instrument and recommissioning runs were conducted until july 2019.results: the measured overall optical throughput of espresso at 550 nm and a seeing of 0.65″ exceeds the 10% mark under nominal astroclimatic conditions. we demonstrate an rv precision of better than 25 cm s-1 during a single night and 50 cm s-1 over several months. these values being limited by photon noise and stellar jitter shows that the performance is compatible with an instrumental precision of 10 cm s-1. no difference has been measured across the uts, neither in throughput nor rv precision.conclusions: the combination of the large collecting telescope area with the efficiency and the exquisite spectral fidelity of espresso opens a new parameter space in rv measurements, the study of planetary atmospheres, fundamental constants, stellar characterization, and many other fields. based on gtos collected at the european southern observatory under eso program(s) 1102.c-0744, 1102.c-0958 and 1104.c-0350 by the espresso consortium. | espresso at vlt. on-sky performance and first results |
this paper presents the gravitational-wave measurement of the hubble constant (h0) using the detections from the first and second observing runs of the advanced ligo and virgo detector network. the presence of the transient electromagnetic counterpart of the binary neutron star gw170817 led to the first standard-siren measurement of h0. here we additionally use binary black hole detections in conjunction with galaxy catalogs and report a joint measurement. our updated measurement is h0 = ${69}_{-8}^{+16}$ km s-1 mpc-1 (68.3% of the highest density posterior interval with a flat-in-log prior) which is an improvement by a factor of 1.04 (about 4%) over the gw170817-only value of ${69}_{-8}^{+17}$ km s-1 mpc-1. a significant additional contribution currently comes from gw170814, a loud and well-localized detection from a part of the sky thoroughly covered by the dark energy survey. with numerous detections anticipated over the upcoming years, an exhaustive understanding of other systematic effects are also going to become increasingly important. these results establish the path to cosmology using gravitational-wave observations with and without transient electromagnetic counterparts. | a gravitational-wave measurement of the hubble constant following the second observing run of advanced ligo and virgo |
low-mass galaxies in the early universe are believed to be the building blocks of present-day galaxies. these fledgling systems likely played a pivotal role in cosmic reionization, a major phase transition from neutral hydrogen to ionized plasma around 600-800 myr after the big bang. however, these galaxies have eluded comprehensive spectroscopic studies owing to their extreme faintness. here we report the first spectroscopic analysis of 8 ultra-faint galaxies during the epoch of reionization with absolute magnitudes between m$_{\rm uv}$ $\sim -17$ to $-15$ mag (down to 0.005 $l^{\star}$). the combination of ultra-deep nirspec (near-infrared spectrograph) observations and the strong gravitational lensing boost of abell~2744 allow us to derive the first spectroscopic constraints on the prevalence of faint galaxies and their ionizing properties during the universe's first billion years. we find that faint galaxies are prodigious producers of ionizing photons with log($\xi_{\rm ion}$/ hz erg$^{-1}$) =$25.8\pm 0.05$, a factor of 4 larger than canonical values. this means that the total rate of ionizing photons produced by galaxies exceeds that needed for reionization, even for modest values of escape fraction ($f_{\rm esc}$ =5%). these findings provide robust evidence that faint galaxies were the main drivers of cosmic reionization at $z\sim7$. | first spectroscopic observations of the galaxies that reionized the universe |
we present the evolution of the mass-metallicity (mz) relation at z = 4-10 derived with 135 galaxies identified in jwst/nirspec data taken from the three major public spectroscopy programs of ero, glass, and ceers. because there are many discrepancies between the flux measurements reported by the early ero studies, we first establish our nirspec data reduction procedure for reliable emission-line flux measurements and errors, successfully explaining balmer decrements with no statistical tensions thorough comparisons with the early ero studies. applying the reduction procedure to the 135 galaxies, we obtain emission-line fluxes for physical property measurements. we confirm that 10 out of the 135 galaxies with [o iii] λ4363 lines have electron temperatures of ≃(1.1-2.3) × 104 k, similar to lower-z star-forming galaxies, which can be explained by heating by young massive stars. we derive the metallicities of the 10 galaxies by a direct method and the rest of the galaxies with strong lines using the metallicity calibrations of nakajima et al. applicable for these low-mass metal-poor galaxies, anchoring the metallicities with the direct-method measurements. we thus obtain the mz relation and star formation rate (sfr)-mz relation over z = 4-10. we find that there is a small evolution of the mz relation from z ~ 2-3 to z = 4-10, while interestingly the sfr-mz relation shows no evolution up to z ~ 8 but a significant decrease at z > 8 beyond the errors this sfr-mz relation decrease at z > 8 may suggest a break of the metallicity equilibrium state via star formation, inflow, and outflow, while further statistical and local-baseline studies are needed for a conclusion. | jwst census for the mass-metallicity star formation relations at z = 4-10 with self-consistent flux calibration and proper metallicity calibrators |
we describe new jwst/nirspec observations of galaxies at z ≳ 7 taken from the ceers survey. previous observations of this area have revealed associations of lyα emitters at redshifts (z = 7.5, 7.7, and 8.7) where the intergalactic medium (igm) is thought to be mostly neutral, leading to suggestions that these systems are situated in large ionized bubbles. we identify 21 z ≳ 7 galaxies with robust redshifts in the ceers data set, including 10 in the lyα associations. their spectra are indicative of very highly ionized and metal poor gas, with line ratios (o32 = 17.84 and ne3o2 = 0.89, linear scale) and metallicity ($12+\log {(\rm {o/h})}=7.84$) that are rarely seen at lower redshifts. we find that the most extreme spectral properties are found in the six z ≳ 7 lyα emitters in the sample. each has a hard ionizing spectrum indicating that their visibility is likely enhanced by efficient ionizing photon production. lyα velocity offsets are found to be very large (≳300 km s-1), likely also contributing to their detectability. we find that lyα in z ≳ 7 galaxies is 6-12 × weaker than in lower redshift samples with matched rest-optical spectral properties. if the bubbles around the lyα emitters are relatively small (≲0.5-1 pmpc), we may expect such significant attenuation of lyα in these ionized regions. we discuss several other effects that may contribute to weaker lyα emission at z ≳ 7. deep spectroscopy of fainter galaxies in the vicinity of the lyα emitters will better characterize the physical scale of the ionized bubbles in this field. | jwst/nirspec spectroscopy of z = 7-9 star-forming galaxies with ceers: new insight into bright lyα emitters in ionized bubbles |
the final evolution of stars in the mass range 70-140 {\text{}}{m}⊙is explored. depending upon their mass loss history and rotation rates, these stars will end their lives as pulsational pair-instability supernovae (ppisn) producing a great variety of observational transients with total durations ranging from weeks to millennia and luminosities from 1041 to over 1044 erg s-1. no nonrotating model radiates more than 5× {10}50 erg of light or has a kinetic energy exceeding 5× {10}51 erg, but greater energies are possible, in principle, in magnetar-powered explosions, which are explored. many events resemble sne ibn, sne icn, and sne iin, and some potential observational counterparts are mentioned. some ppisn can exist in a dormant state for extended periods, producing explosions millennia after their first violent pulse. these dormant supernovae contain bright wolf-rayet stars, possibly embedded in bright x-ray and radio sources. the relevance of ppisn to supernova impostors like eta carinae, to superluminous supernovae, and to sources of gravitational radiation is discussed. no black holes between 52 and 133 {\text{}}{m}⊙are expected from stellar evolution in close binaries. | pulsational pair-instability supernovae |
we discuss new constraints on the epoch of cosmic reionization and test the assumption that most of the ionizing photons responsible arose from high-redshift star-forming galaxies. good progress has been made in charting the end of reionization through spectroscopic studies of z ≃ 6-8 qsos, gamma-ray bursts, and galaxies expected to host lyα emission. however, the most stringent constraints on its duration have come from the integrated optical depth, τ, of thomson scattering to the cosmic microwave background. using the latest data on the abundance and luminosity distribution of distant galaxies from hubble space telescope imaging, we simultaneously match the reduced value τ =0.066+/- 0.012 recently reported by the planck collaboration and the evolving neutrality of the intergalactic medium with a reionization history within 6≲ z≲ 10, thereby reducing the requirement for a significant population of very high redshift (z\gg 10) galaxies. our analysis strengthens the conclusion that star-forming galaxies dominated the reionization process and has important implications for upcoming 21 cm experiments and searches for early galaxies with the james webb space telescope. | cosmic reionization and early star-forming galaxies: a joint analysis of new constraints from planck and the hubble space telescope |
we show a simple, systematic and direct approach to decoupling gravitational sources in general relativity. as a direct application, a robust and simple way to generate anisotropic solutions for self-gravitating systems from perfect fluid solutions is presented. | decoupling gravitational sources in general relativity: from perfect to anisotropic fluids |
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