arXiv subjects

Jeff J. Andrews

Publications and source records attributed to Jeff J. Andrews.

At least 55 records · Page 3Linked to original sources

arXiv2022

POSYDON: A General-Purpose Population Synthesis Code with Detailed Binary-Evolution Simulations

Most massive stars are members of a binary or a higher-order stellar systems, where the presence of a binary companion can decisively alter their evolution via binary interactions. Interacting binaries are also important astrophysical laboratories for the study of compact objects. Binary population synthesis studies have been used extensively over the last two decades to interpret observations of compact-object binaries and to decipher the physical processes that lead to their formation. Here, we present POSYDON, a novel, binary population synthesis code that incorporates full stellar-structure and binary-evolution modeling, using the MESA code, throughout the whole evolution of the binaries. The use of POSYDON enables the self-consistent treatment of physical processes in stellar and binary evolution, including: realistic mass-transfer calculations and assessment of stability, internal angular-momentum transport and tides, stellar core sizes, mass-transfer rates and orbital periods. This paper describes the detailed methodology and implementation of POSYDON, including the assumed physics of stellar- and binary-evolution, the extensive grids of detailed single- and binary-star models, the post-processing, classification and interpolation methods we developed for use with the grids, and the treatment of evolutionary phases that are not based on pre-calculated grids. The first version of POSYDON targets binaries with massive primary stars (potential progenitors of neutron stars or black holes) at solar metallicity.

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arXiv2022

A Sample of Neutron Star and Black Hole Binaries Detected through Gaia DR3 Astrometry

With its exquisite astrometric precision, the latest Gaia data release includes $\sim$$10^5$ astrometric binaries, each of which have measured orbital periods, eccentricities, and the Thiele-Innes orbital parameters. Using these and an estimate of the luminous stars' masses, we derive the companion stars' masses, from which we identify a sample of 24 binaries in long period orbits ($P_{\rm orb}\sim{\rm yrs}$) with a high probability of hosting a massive ($>$1.4 $M_{\odot}$), dark companion: a neutron star (NS) or black hole (BH). The luminous stars in these binaries tend to be F-, G-, and K-dwarfs with the notable exception of one hot subdwarf. Follow-up spectroscopy of eight of these stars shows no evidence for contamination by white dwarfs or other luminous stars. The dark companions in these binaries span a mass range of 1.35-2.7 $M_{\odot}$ and therefore likely includes both NSs and BHs without a significant mass gap in between. Furthermore, the masses of several of these objects are $\simeq$1.7 $M_{\odot}$, similar to the mass of at least one of the merging compact objects in GW190425. Given that these orbits are too wide for significant mass accretion to have occurred, this sample implies that some NSs are born heavy ($\gtrsim$1.5 $M_{\odot}$). Additionally, the low orbital velocities ($\lesssim$20 km s$^{-1}$) of these binaries requires that at least some heavy NSs receive low natal kicks, otherwise they would have been disrupted during core collapse. Although none will become gravitational wave sources within a Hubble time, these systems will be exceptionally useful for testing binary evolution theory.

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arXiv2022

Weighing the Darkness III: How Gaia Could, but Probably Won't, Astrometrically Detect Free-Floating Black Holes

The gravitational pull of an unseen companion to a luminous star is well-known to cause deviations to the parallax and proper motion of a star. In a previous paper in this series, we argue that the astrometric mission Gaia can identify long-period binaries by precisely measuring these arcs. An arc in a star's path can also be caused by a fly-by -- the hyperbolic encounter with another massive object. We quantify the apparent acceleration over time induced by a companion star as a function of the impact parameter, velocity of interaction, and companion mass. In principle, Gaia could be used to astrometrically identify the contribution of massive compact halo objects to the local dark matter potential of the Milky Way. However, after quantifying their rate and Gaia's sensitivity, we find that fly-bys are so rare that Gaia will probably never observe one. Therefore every star in the Gaia database exhibiting astrometric acceleration is likely in a long-period binary with another object. Nevertheless, we show how intermediate mass black holes, if they exist in the Solar Neighborhood, could be detected by the anomalously large accelerations they induce on nearby stars.

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arXiv2022

A Young, Low-Density Stellar Stream in the Milky Way Disk: Theia 456

Our view of the variety of stellar structures pervading the local Milky Way has been transformed by the application of clustering algorithms to the Gaia catalog. In particular, several stellar streams have been recently discovered that are comprised of hundreds to thousands of stars and span several hundred parsecs. We analyze one such structure, Theia 456, a low-density stellar stream extending nearly 200 pc and 20$^{\circ}$ across the sky. By supplementing Gaia astrometric data with spectroscopic metallicities from LAMOST and photometric rotation periods from the Zwicky Transient Facility (ZTF) and the Transiting Exoplanet Survey Satellite (TESS), we establish Theia 456's radial velocity coherence, and we find strong evidence that members of Theia 456 have a common age ($\simeq$175 Myr), common dynamical origin, and formed from chemically homogeneous pre-stellar material ([Fe/H] = $-$0.07 dex). Unlike well-known stellar streams in the Milky Way, which are in its halo, Theia 456 is firmly part of the thin disk. If our conclusions about Theia 456 can be applied to even a small fraction of the remaining $\simeq$8300 independent structures in the Theia catalog, such low-density stellar streams may be ubiquitous. We comment on the implications this has for the nature of star-formation throughout the Galaxy.

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arXiv2022

Constraining Black Hole Natal Kicks with Astrometric Microlensing

Multiple pieces of evidence suggest that neutron stars receive large kicks when formed from the remnant of a collapsing star. However, the evidence for whether black holes (BH) receive natal kicks is less clear, reliant on weak constraints from the analysis of BH X-ray binaries and massive runaway and walkaway stars. Here we show for the first time that recent microlensing detections offer a new method for measuring the kicks BHs receive at birth. When a BH is identified through both photometric and astrometric microlensing and when the lensed star has a known distance and proper motion, the mass, distance and proper motion of the BH can be determined. We study the runaway velocities for components of eccentric binaries disrupted during a supernova, finding the peculiar velocity correlates strongly with the kick a BH received a birth, typically within 20\%, even when the natal kick is smaller than the orbital velocity. Therefore, by measuring the peculiar velocity of a BH or other compact object that formed from a binary that disrupted during core collapse, we are in effect measuring the natal kick that object received. We focus on MOA-2011-BLG-191/OGLE-2011-BLG-0462, an isolated, single BH detected by microlensing and consider a range of possible formation scenarios, including its formation from the disruption of a binary during a supernova event. We determine that MOA-2011-BLG-191/OGLE-2011-BLG-0462 has a Milky Way orbit consistent with a thick disk population, but if it were formed within the kinematic thin disk it received a natal kick $\lesssim$100 km s$^{-1}$.

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arXiv2022

Gaia May Detect Hundreds of Well-characterised Stellar Black Holes

Detection of black holes (BHs) with detached luminous companions (LCs) can be instrumental in connecting the BH properties with their progenitors' since the latter can be inferred from the observable properties of the LC. Past studies showed the promise of Gaia astrometry in detecting BH-LC binaries. We build upon these studies by: 1) initialising the zero-age binary properties based on realistic, metallicity-dependent star-formation history in the Milky Way (MW), 2) evolving these binaries to current epoch to generate realistic MW populations of BH-LC binaries, 3) distributing these binaries in the MW preserving the complex age-metallicity-Galactic position correlations, 4) accounting for extinction and reddening using three-dimensional dust maps, 5) examining the extended Gaia mission's ability to resolve BH-LC binaries. We restrict ourselves to detached BH-LC binaries with orbital period <10 yr such that Gaia can observe at least one full orbit. We find: 1) the extended Gaia mission can astrometrically resolve 30-300 detached BH-LC binaries depending on our assumptions of supernova physics and astrometric detection threshold; 2) Gaia's astrometry alone can indicate BH candidates for 10-100 BH-LC binaries by constraining the dark primary mass >3 Msun; 3) distributions of observables including orbital periods, eccentricities, and component masses are sensitive to the adopted binary evolution model, hence can directly inform binary evolution models. Finally, we comment on the potential to further characterise these BH binaries through radial velocity measurements and observation of X-ray counterparts.

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arXiv2021

Probing the progenitors of spinning binary black-hole mergers with long gamma-ray bursts

Long-duration gamma-ray bursts are thought to be associated with the core-collapse of massive, rapidly spinning stars and the formation of black holes. However, efficient angular momentum transport in stellar interiors, currently supported by asteroseismic and gravitational-wave constraints, leads to predominantly slowly-spinning stellar cores. Here, we report on binary stellar evolution and population synthesis calculations, showing that tidal interactions in close binaries not only can explain the observed sub-population of spinning, merging binary black holes but also lead to long gamma-ray bursts at the time of black-hole formation. Given our model calibration against the distribution of isotropic-equivalent energies of luminous long gamma-ray bursts, we find that ~10% of the GWTC-2 reported binary black holes had a luminous long gamma-ray burst associated with their formation, with GW190517 and GW190719 having a probability of ~85% and ~60%, respectively, being among them. Moreover, given an assumption about their average beaming fraction, our model predicts the rate density of long gamma-ray bursts, as a function of redshift, originating from this channel. For a constant beaming fraction $f_\mathrm{B}\sim 0.05$ our model predicts a rate density comparable to the observed one, throughout the redshift range, while, at redshift $z \in [0,2.5]$, a tentative comparison with the metallicity distribution of observed LGRB host galaxies implies that between 20% to 85% of the observed long gamma-ray bursts may originate from progenitors of merging binary black holes. The proposed link between a potentially significant fraction of observed, luminous long gamma-ray bursts and the progenitors of spinning binary black-hole mergers allows us to probe the latter well outside the horizon of current-generation gravitational wave observatories, and out to cosmological distances.

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arXiv2021

Weighing the Darkness II: Astrometric Measurement of Partial Orbits with Gaia

Over the course of several years, stars trace helical trajectories as they traverse across the sky due to the combined effects of proper motion and parallax. It is well known that the gravitational pull of an unseen companion can cause deviations to these tracks. Several studies have pointed out that the astrometric mission Gaia will be able to identify a slew of new exoplanets, stellar binaries, and compact object companions with orbital periods as short as tens of days to as long as Gaia's lifetime. Here, we use mock astrometric observations to demonstrate that Gaia can identify and characterize black hole companions to luminous stars with orbital periods longer than Gaia's lifetime. Such astrometric binaries have orbital periods too long to exhibit complete orbits, and instead are identified through curvature in their characteristic helical paths. By simultaneously measuring the radius of this curvature and the orbital velocity, constraints can be placed on the underlying orbit. We quantify the precision with which Gaia can measure orbital accelerations and apply that to model predictions for the population of black holes orbiting stars in the stellar neighborhood. Although orbital degeneracies imply that many of the accelerations induced by hidden black holes could also be explained by faint low-mass stars, we discuss how the nature of certain putative black hole companions can be confirmed with high confidence using Gaia data alone.

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arXiv2021

The Heraklion Extragalactic Catalogue (HECATE): a value-added galaxy catalogue for multi-messenger astrophysics

We present the Heraklion Extragalactic Catalogue, or HECATE, an all-sky value-added galaxy catalogue, aiming to facilitate present and future multi-wavelength and multi-messenger studies in the local Universe. It contains 204,733 galaxies up to a redshift of 0.047 (D<200 Mpc), and it is >50% complete in terms of the B-band luminosity density at distances in the 0-170 Mpc range. By incorporating and homogenising data from astronomical databases and multi-wavelength surveys, the catalogue offers positions, sizes, distances, morphological classifications, star-formation rates, stellar masses, metallicities, and nuclear activity classifications. This wealth of information can enable a wide-range of applications, such as: (i) demographic studies of extragalactic sources, (ii) initial characterisation of transient events, and (iii) searches for electromagnetic counterparts of gravitational-wave events. The catalogue is publicly available to the community at a dedicated portal, which will also host future extensions in terms of the covered volume, and data products.

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arXiv2021

Targeted modeling of GW150914's binary black hole source with dart_board

We present a new method to extract statistical constraints on the progenitor properties and formation channels of individual gravitational-wave sources. Although many different models have been proposed to explain the binary black holes detected by the LIGO Scientific and Virgo Collaboration (LVC), formation through isolated binary evolution remains the best explored channel. Under the assumption of formation through binary evolution, we use the statistical wrapper dart_board coupled with the rapid binary evolution code COSMIC to model the progenitor of GW150914, the first gravitational-wave signal detected by the LVC. Our Bayesian method combines the likelihood generated from the gravitational-wave signal with a prior describing the population of stellar binaries, and the Universe's star-formation and metallicity evolution. We find that the dominant evolutionary channel for GW150914 did not involve a common-envelope phase, but instead the system most probably (70%-90%) formed through stable mass transfer. This result is robust against variations of various model parameters, and it is reversed only when dynamical instability in binaries becomes more likely when a strict condition favoring common envelopes is adopted. Our analysis additionally provides a quantitative description of the progenitors relevant to each channel.

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arXiv2021

The impact of mass-transfer physics on the observable properties of field binary black hole populations

We study the impact of mass-transfer physics on the observable properties of binary black hole populations formed through isolated binary evolution. We investigate the impact of mass-accretion efficiency onto compact objects and common-envelope efficiency on the observed distributions of $χ_{eff}$, $M_{chirp}$ and $q$. We find that low common envelope efficiency translates to tighter orbits post common envelope and therefore more tidally spun up second-born black holes. However, these systems have short merger timescales and are only marginally detectable by current gravitational-waves detectors as they form and merge at high redshifts ($z\sim 2$), outside current detector horizons. Assuming Eddington-limited accretion efficiency and that the first-born black hole is formed with a negligible spin, we find that all non-zero $χ_{eff}$ systems in the detectable population can come only from the common envelope channel as the stable mass-transfer channel cannot shrink the orbits enough for efficient tidal spin-up to take place. We find the local rate density ($z\simeq 0.01$) for the common envelope channel is in the range $\sim 17-113~Gpc^{-3}yr^{-1}$ considering a range of $α_{CE} \in [0.2,5.0]$ while for the stable mass transfer channel the rate density is $\sim 25~Gpc^{-3}yr^{-1}$. The latter drops by two orders of magnitude if the mass accretion onto the black hole is not Eddington limited because conservative mass transfer does not shrink the orbit as efficiently as non-conservative mass transfer does. Finally, using GWTC-2 events, we constrain the lower bound of branching fraction from other formation channels in the detected population to be $\sim 0.2$. Assuming all remaining events to be formed through either stable mass transfer or common envelope channels, we find moderate to strong evidence in favour of models with inefficient common envelopes.

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arXiv2020

COSMIC Variance in Binary Population Synthesis

The formation and evolution of binary stars is a critical component of several fields in astronomy. The most numerous sources for gravitational wave observatories are inspiraling and/or merging compact binaries, while binary stars are present in nearly every electromagnetic survey regardless of the target population. Simulations of large binary populations serve to both predict and inform observations of electromagnetic and gravitational wave sources. Binary population synthesis is a tool that balances physical modeling with simulation speed to produce large binary populations on timescales of days. We present a community-developed binary population synthesis suite: COSMIC which is designed to simulate compact-object binary populations and their progenitors. As a proof of concept, we simulate the Galactic population of compact binaries and their gravitational wave signal observable by the Laser Interferometer Space Antenna (LISA). We find that $\sim10^8$ compact binaries reside in the Milky Way today, while $\sim10^4$ of them may be resolvable by LISA.

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arXiv2020

A census of ultraluminous X-ray sources in the local Universe

Using the Chandra Source Catalog 2.0 and a newly compiled catalogue of galaxies in the local Universe, we deliver a census of ultraluminous X-ray source (ULX) populations in nearby galaxies. We find 629 ULX candidates in 309 galaxies with distance smaller than 40\,Mpc. The foreground/background contamination is ${\sim}20\%$. The ULX populations in bona-fide star-forming galaxies scale on average with star-formation rate (SFR) and stellar mass ($M_\star$) such that the number of ULXs per galaxy is $0.45^{+0.06}_{-0.09}\times\frac{\rm SFR}{\rm M_\odot\,yr^{-1}}{+}3.3^{+3.8}_{-3.2}\times\frac{M_\star}{\rm M_\odot}$. The scaling depends strongly on the morphological type. This analysis shows that early spiral galaxies contain an additional population of ULXs that scales with $M_\star$. We also confirm the strong anti-correlation of the ULX rate with the host galaxy's metallicity. In the case of early-type galaxies we find that there is a non-linear dependence of the number of ULXs with $M_\star$, which is interpreted as the result of star-formation history differences. Taking into account age and metallicity effects, we find that the predictions from X-ray binary population synthesis models are consistent with the observed ULX rates in early-type galaxies, as well as, spiral/irregular galaxies.

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arXiv2020

Mass Ratios of Merging Double Neutron Stars as Implied by the Milky Way Population

Of the seven known double neutron stars (DNS) with precisely measure masses in the Milky Way that will merge within a Hubble time, all but one has a mass ratio, $q$, close to unity. Recently, precise measurements of three post-Keplerian parameters in the DNS J1913$+$1102 constrain this system to have a significantly non-unity mass ratio of 0.78$\pm$0.03. One may be tempted to conclude that approximately one out of seven (14\%) DNS mergers detected by gravitational wave observatories will have mass ratios significantly different from unity. However J1913$+$1102 has a relatively long merger time of 470 Myr. We show that when merger times and observational biases are taken into account, the population of Galactic DNSs imply that $\simeq98\%$ of all merging DNSs will have $q>$0.9. We then apply two separate fitting formulas informed by 3D hydrodynamic simulations of DNS mergers to our results on Galactic DNS masses, finding that either $\simeq$0.004 ${M_{\odot}}$ or $\simeq$0.010 ${M_{\odot}}$ of material will be ejected at merger, depending on which formula is used. These ejecta masses have implications for both the peak bolometric luminosities of electromagnetic counterparts (which we find to be $\sim$10$^{41}$ erg s$^{-1}$) as well as the $r$-process enrichment of the Milky Way.

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arXiv2020

The ELM Survey. VIII. 98 Double White Dwarf Binaries

We present the final sample of 98 detached double white dwarf (WD) binaries found in the Extremely Low Mass (ELM) Survey, a spectroscopic survey targeting <0.3 Msun He-core WDs completed in the Sloan Digital Sky Survey footprint. Over the course of the survey we observed ancillary low mass WD candidates like GD278, which we show is a P=0.19 d double WD binary, as well as candidates that turn out to be field blue straggler/subdwarf A-type stars with luminosities too large to be WDs given their Gaia parallaxes. Here, we define a clean sample of ELM WDs that is complete within our target selection and magnitude range 15<g_0<20 mag. The measurements are consistent with 100% of ELM WDs being 0.0089 < P < 1.5 d double WD binaries, 35% of which belong to the Galactic halo. We infer these are mostly He+CO WD binaries given the measurement constraints. The merger rate of the observed He+CO WD binaries exceeds the formation rate of stable mass transfer AM CVn binaries by a factor of 25, and so the majority of He+CO WD binaries must experience unstable mass transfer and merge. The shortest-period systems like J0651+2844 are signature {\it LISA} verification binaries that can be studied with gravitational waves and light.

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arXiv2019

LISA and the Existence of a Fast-Merging Double Neutron Star Formation Channel

Using a Milky Way double neutron star (DNS) merger rate of 210 Myr$^{-1}$, as derived by the Laser Interferometer Gravitational-Wave Observatory (LIGO), we demonstrate that the Laser Interferometer Space Antenna (LISA) will detect on average 240 (330) DNSs within the Milky Way for a 4-year (8-year) mission with a signal-to-noise ratio greater than 7. Even adopting a more pessimistic rate of 42 Myr$^{-1}$, as derived by the population of Galactic DNSs, we find a significant detection of 46 (65) Milky Way DNSs. These DNSs can be leveraged to constrain formation scenarios. In particular, traditional NS-discovery methods using radio telescopes are unable to detect DNSs with $P_{\rm orb}$ $\lesssim$1 hour (merger times $\lesssim$10 Myr). If a fast-merging channel exists that forms DNSs at these short orbital periods, LISA affords, perhaps, the only opportunity to observationally characterize these systems; we show that toy models for possible formation scenarios leave unique imprints on DNS orbital eccentricities, which may be measured by LISA for values as small as $\sim$10$^{-2}$.

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arXiv2019

Weighing the Darkness: Astrometric Mass Measurement of Hidden Stellar Companions using Gaia

In astrometric binaries, the presence of a dark, unseen star can be inferred from the gravitational pull it induces on its luminous binary companion. While the orbit of such binaries can be characterized with precise astrometric measurements, constraints made from astrometry alone are not enough to measure the component masses. In this work, we determine the precision with which Gaia can astrometrically measure the orbits and -- with additional observations -- the component masses, for luminous stars hosting hidden companions. Using realistic mock Gaia observations, we find that Gaia can precisely measure the orbits of binaries hosting hidden brown-dwarfs out to tens of pc and hidden white dwarf and neutron star companions at distances as far as several hundred pc. Heavier black hole companions may be measured out to 1 kpc or farther. We further determine how orbital period affects this precision, finding that Gaia can characterize orbits with periods as short as 10 days and as long as a few 10$^3$ days, with the best measured orbits having periods just short of Gaia's mission lifetime. Extending Gaia's nominal five-year mission lifetime by an additional five years not only allows for the measurement of longer period orbits, but those longer period binaries can be seen at even greater distances.

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arXiv2019

Did GW170817 harbor a pulsar?

If the progenitor of GW170817 harbored a pulsar, then a Poynting flux dominated bow-shock cavity would have been expected to form around the traveling binary. The characteristic size of this evacuated region depends strongly on the spin-down evolution of the pulsar companion, which in turn depends on the merging timescale of the system. If this evacuated region is able to grow to a sufficiently large scale, then the deceleration of the jet, and thus the onset of the afterglow, would be noticeably delayed. The first detection of afterglow emission, which was uncovered 9.2 days after the $γ$-ray burst trigger, can thus be used to constrain the size of a pre-existing pulsar-wind cavity. We use this information, together with a model of the jet to place limits on the presence of a pulsar in GW170817 and discuss the derived constraints in the context of the observed double neutron star binary population. We find that the majority of Galactic systems that are close enough to merge within a Hubble time would have carved a discernibly large pulsar-wind cavity, inconsistent with the onset timescale of the X-ray afterglow of GW170817. Conversely, the recently detected system J1913+1102, which host a low-luminosity pulsar, provides a congruous Milky Way analog of GW170817's progenitor model. This study highlights the potential of the proposed observational test for gaining insight into the origin of double neutron star binaries, in particular if the properties of Galactic systems are representative of the overall merging population.

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