arXiv subjects

Jeff J. Andrews

Publications and source records attributed to Jeff J. Andrews.

At least 37 records · Page 2Linked to original sources

arXiv2024

Irregularly Sampled Time Series Interpolation for Detailed Binary Evolution Simulations

Modeling of large populations of binary stellar systems is an intergral part of a many areas of astrophysics, from radio pulsars and supernovae to X-ray binaries, gamma-ray bursts, and gravitational-wave mergers. Binary population synthesis codes that employ self-consistently the most advanced physics treatment available for stellar interiors and their evolution and are at the same time computationally tractable have started to emerge only recently. One element that is still missing from these codes is the ability to generate the complete time evolution of binaries with arbitrary initial conditions using pre-computed three-dimensional grids of binary sequences. Here we present a highly interpretable method, from binary evolution track interpolation. Our method implements simulation generation from irregularly sampled time series. Our results indicate that this method is appropriate for applications within binary population synthesis and computational astrophysics with time-dependent simulations in general. Furthermore we point out and offer solutions to the difficulty surrounding evaluating performance of signals exhibiting extreme morphologies akin to discontinuities.

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arXiv2024

An Empirical Framework Characterizing the Metallicity and Star-Formation History Dependence of X-ray Binary Population Formation and Emission in Galaxies

We present a new empirical framework modeling the metallicity and star-formation history (SFH) dependence of X-ray luminous ($L > 10^{36}$ ergs s$^{-1}$) point-source population luminosity functions (XLFs) in normal galaxies. We expect the X-ray point-source populations are dominated by X-ray binaries (XRBs), with contributions from supernova remnants near the low luminosity end of our observations. Our framework is calibrated using the collective statistical power of 3,731 X-ray detected point-sources within 88 Chandra-observed galaxies at $D <$ 40 Mpc that span broad ranges of metallicity ($Z \approx$ 0.03-2 $Z_\odot$), SFH, and morphology (dwarf irregulars, late-types, and early-types). Our best-fitting models indicate that the XLF normalization per unit stellar mass declines by $\approx$2-3 dex from 10 Myr to 10 Gyr, with a slower age decline for low-metallicity populations. The shape of the XLF for luminous X-ray sources ($L < 10^{38}$ ergs s$^{-1}$) significantly steepens with increasing age and metallicity, while the lower-luminosity XLF appears to flatten with increasing age. Integration of our models provide predictions for X-ray scaling relations that agree very well with past results presented in the literature, including, e.g., the $L_{\rm X}$-SFR-$Z$ relation for high-mass XRBs (HMXBs) in young stellar populations as well as the $L_{\rm X}/M_\star$ ratio observed in early-type galaxies that harbor old populations of low-mass XRBs (LMXBs). The model framework and data sets presented in this paper further provide unique benchmarks that can be used for calibrating binary population synthesis models.

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arXiv2024

The Formation of Black Holes in Non-interacting, Isolated Binaries. Gaia Black Holes as Calibrators of Stellar Winds From Massive Stars

Context. The black holes discovered using Gaia, especially Gaia BH1 and BH2, have low mass companions of solar-like metallicity in wide orbits. For standard isolated binary evolution formation channels including interactions such an extreme mass ratio is unexpected; especially in orbits of hundreds to thousands of days. Aims. Here, we investigate a non-interacting formation path for isolated binaries to explain the formation of Gaia BH1 and BH2. Methods. We use single star models computed with MESA to constrain the main characteristics of possible progenitors of long-period black hole binaries like Gaia BH1 and BH2. Then, we incorporate these model grids into the binary population synthesis code POSYDON, to explore whether the formation of the observed binaries at solar metallicity is indeed possible. Results. We find that winds of massive stars ($\gtrsim 80\,M_\odot$), especially during the Wolf-Rayet phase, tend to cause a plateau in the initial stellar mass to final black hole mass relation (at about $13\,M_\odot$ in our default wind prescription). However, stellar winds at earlier evolutionary phases are also important at high metallicity, as they prevent the most massive stars from expanding ($<100\,R_\odot$) and filling their Roche lobe. Consequently, the strength of the applied winds affects the range of the final black hole masses in non-interacting binaries, making it possible to form systems similar to Gaia BH1 and BH2. Conclusions. We deduce that wide binaries with a black hole and a low mass companion can form at high metallicity without binary interactions. There could be hundreds of such systems in the Milky Way. The mass of the black hole in binaries evolved through the non-interacting channel can potentially provide insights into the wind strength during the progenitors evolution.

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arXiv2024

Fundamental Tests of White Dwarf Cooling Physics with Wide Binaries

We present follow-up spectroscopy and a detailed model atmosphere analysis of 29 wide double white dwarfs, including eight systems with a crystallized C/O core member. We use state-of-the-art evolutionary models to constrain the physical parameters of each star, including the total age. Assuming that the members of wide binaries are coeval, any age difference between the binary members can be used to test the cooling physics for white dwarf stars, including potential delays due to crystallization and $^{22}$Ne distillation. We use our control sample of 14 wide binaries with non-crystallized members to show that this method works well; the control sample shows an age difference of only $Δ$Age = $-0.03 \pm$ 0.15 Gyr between its members. For the eight crystallized C/O core systems we find a cooling anomaly of $Δ$Age= 1.13$^{+1.20}_{-1.07}$ Gyr. Even though our results are consistent with a small additional cooling delay ($\sim1$ Gyr) from $^{22}$Ne distillation and other neutron-rich impurities, the large uncertainties make this result not statistically significant. Nevertheless, we rule out cooling delays longer than 3.6 Gyr at the 99.7% ($3σ$) confidence level for 0.6-0.9 $M_{\odot}$ white dwarfs. Further progress requires larger samples of wide binaries with crystallized massive white dwarf members. We provide a list of subgiant + white dwarf binaries that could be used for this purpose in the future.

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arXiv2024

To Be or not to Be: the role of rotation in modeling Galactic Be X-ray Binaries

Be X-ray binaries (Be-XRBs) are one of the largest subclasses of high-mass X-ray binaries, comprised of a rapidly rotating Be star and neutron star companion in an eccentric orbit, intermittently accreting material from a decretion disk around the donor. Originating from binary stellar evolution, Be-XRBs are of significant interest to binary population synthesis (BPS) studies, encapsulating the physics of supernovae, common envelope, and mass transfer (MT). Using the state-of-the-art BPS code, POSYDON, which relies on pre-computed grids of detailed binary stellar evolution models, we investigate the Galactic Be-XRB population. POSYDON incorporates stellar rotation self-consistently during MT phases, enabling detailed examination of the rotational distribution of Be stars in multiple phases of evolution. Our fiducial BPS and Be-XRB model align well with the orbital properties of Galactic Be-XRBs, emphasizing the role of rotational constraints. Our modeling reveals a rapidly rotating population ($ω/ω_\mathrm{crit} \gtrsim 0.3$) of Be-XRB-like systems with a strong peak at intermediate rotation rates ($ω/ω_\mathrm{crit} \simeq 0.6$) in close alignment with observations. All Be-XRBs undergo a MT phase before the first compact object forms, with over half experiencing a second MT phase from a stripped helium companion (Case BB). Computing rotationally-limited MT efficiencies and applying them to our population, we derive a physically motivated MT efficiency distribution, finding that most Be-XRBs have undergone highly non-conservative MT ($\barβ_\mathrm{rot} \simeq 0.05$). Our study underscores the importance of detailed angular momentum modeling during MT in interpreting Be-XRB populations, emphasizing this population as a key probe for the stability and efficiency of MT in interacting binaries.

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arXiv2024

Theia 456: Tidally Shredding an Open Cluster

The application of clustering algorithms to the Gaia astrometric catalog has revolutionized our census of stellar populations in the Milky Way, including the discovery of many new, dispersed structures. We focus on one such structure, Theia 456 (COIN-Gaia-13), a loosely bound collection of ~320 stars spanning ~120 pc that has previously been shown to exhibit kinematic, chemical, and gyrochronal coherency, indicating a common origin. We obtain follow-up radial velocities and supplement these with Gaia astrometry to perform an in-depth dynamical analysis of Theia 456. By integrating stellar orbits through a Milky Way potential, we find the currently dispersed structure coalesced into a small cluster in the past. Via Bayesian modeling, we derive a kinematic age of 245 +/- 3 Myr (statistical), a half-mass radius of 9 +/- 2 pc, and an initial one-dimensional velocity dispersion of 0.14 +/- 0.02 km/s. Our results are entirely independent of model isochrones, details of stellar evolution, and internal cluster dynamics, and the statistical precision in our age derivation rivals that of the most precise age-dating techniques known today, though our imperfect knowledge of the Milky Way potential and simple spherical model for Theia 456 at birth add additional uncertainties. Using posterior predictive checking, we confirm these results are robust under reasonable variations to the Milky Way potential. Such low density structures that are disrupted by the Galactic tides before virializing may be ubiquitous, signifying that Theia 456 is a valuable benchmark for studying the dynamical history of stellar populations in the Milky Way.

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arXiv2024

Formation of Wind-Fed Black Hole High-mass X-ray Binaries: The Role of Roche-lobe-Overflow Post Black-Hole Formation

The three dynamically confirmed wind-fed black hole high-mass X-ray binaries (BH-HMXBs) are suggested to all contain a highly spinning black hole (BH). However, based on the theories of efficient angular momentum transport inside the stars, we expect that the first-born BHs in binary systems should have low spins, which is consistent with gravitational-wave observations. As a result, the origin of the high BH spins measured in wind-fed BH-HMXBs remains a mystery. In this paper, we conduct a binary population synthesis study on wind-fed BH-HMXBs at solar metallicity with the use of the newly developed code POSYDON, considering three scenarios for BH accretion: Eddington-limited, moderately super-Eddington, and fully conservative accretion. Taking into account the conditions for accretion-disk formation, we find that regardless of the accretion model, these systems are more likely to have already experienced a phase of Roche-lobe overflow after the BH formation. To account for the extreme BH spins, highly conservative accretion onto BHs is required, when assuming the accreted material carries the specific angular momentum at the innermost stable orbit. Besides, in our simulations we found that the systems with donor stars within the mass range of $10-20\,M_{\odot}$ are prevalent, posing a challenge in explaining simultaneously all observed properties of the BH-HMXB in our Galaxy, Cygnus X-1, and potentially hinting that the accretion efficiency onto non-degenerate stars, before the formation of the BH, is also more conservative than assumed in our simulations.

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arXiv2024

A Lack of Mass-Gap Compact Object Binaries in APOGEE

Depending principally on mass, the compact object remnant left behind after a star's life may be a white dwarf (WD), neutron star (NS), or black hole (BH). While we have large samples of each of these remnants, we lack knowledge of the exact conditions separating these outcomes. The boundary between low-mass BHs and massive NSs is particularly poorly understood, as few objects between 2-5 $M_\odot$ are known. To probe this regime, we search the APOGEE DR17 dataset of 657,000 unique stars for binary systems with one stellar component that exhibit large radial velocity shifts over multiple observations. We identify 4751 likely binary systems, and estimate a minimum mass for each system's "invisible companion" under the assumption of tidal synchronization. Two systems have companion masses $\gtrsim$ 2 $M_\odot$, although we conclude that neither are good candidates for possessing a mass-gap NS or BH companions.

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arXiv2023

Exploring the nature of ultra-luminous X-ray sources across stellar population ages using detailed binary evolution calculations

Ultra-luminous X-ray sources (ULXs) are sources observed to exceed the Eddington limit of a stellar-mass black hole (BH). A fraction of ULX sources show X-ray pulses which are evidence for accreting neutron stars (NSs). Theoretical studies have suggested that NSs dominate the compact objects of intrinsic ULXs, even though the majority of observed sample is non-pulsating, implying that X-ray pulses from many NS ULXs are unobservable. We use POSYDON to generate and study X-ray binary populations spanning starburst ages 5 to 1000Myr. Following theoretical predictions for the alignment of the NS spin axis with the accretion disc, we estimate the required accreted mass in ULXs so that the alignment suppresses observable X-ray pulses. While the properties of ULXs are sensitive to model assumptions, there are certain trends that the populations follow. Young and old stellar populations are dominated by BH and NS accretors, respectively. The donors go from massive H-rich main-sequence (MS) stars in young populations (<100Myr) to low-mass post-MS H-rich stars in older populations (>100Myr), with stripped He-rich giant stars dominating the populations at around 100Myr. In addition, we find that NS ULXs exhibit stronger geometrical beaming than BH ULXs, leading to an under-representation of NS accretors in observed populations. Coupled with our finding that X-ray pulses are suppressed in at least 60% of the NS ULXs, we suggest that the observed fraction of ULXs with detectable X-ray pulses is very small, in agreement with observations. This study investigates the effects of age on ULXs as well as the effects of different model assumptions on ULX demographics. We show that geometrical beaming and the mass-accretion phase are critical aspects of understanding ULX observations. Our results suggest that even though most ULXs have accreting NSs, those with observable X-ray pulses would be very few.

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arXiv2023

Total r-process Yields of Milky Way Neutron Star Mergers

While it is now known that double neutron star binary systems (DNSs) are copious producers of heavy elements, there remains much speculation about whether they are the sole or even principal site of rapid neutron-capture (r-process) nucleosynthesis, one of the primary ways in which heavy elements are produced. The occurrence rates, delay times, and galactic environments of DNSs hold sway over estimating their total contribution to the elemental abundances in the Solar system and the Galaxy. Furthermore, the expected elemental yield for DNSs may depend on the merger parameters themselves -- such as their stellar masses and radii -- which is not currently considered in many galactic chemical evolution models. Using the characteristics of the observed sample of DNSs in the Milky Way as a guide, we predict the expected nucleosynthetic yields that a population of DNSs would produce upon merger, and we compare that nucleosynthetic signature to the heavy-element abundance pattern of the Solar system elements. We find that with our current models, the present DNS population favors production of the lighter r-process elements, while underproducing the heaviest elements relative to the Solar system. This inconsistency could imply an additional site for the heaviest elements or a population of DNSs much different from that observed today.

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arXiv2023

From ZAMS to Merger: Detailed Binary Evolution Models of Coalescing Neutron Star-Black Hole Systems at Solar Metallicity

Neutron star $-$ black hole (NSBH) merger events bring us new opportunities to constrain theories of stellar and binary evolution, and understand the nature of compact objects. In this work, we investigate the formation of merging NSBH binaries at solar metallicity by performing a binary population synthesis study of merging NSBH binaries with the newly developed code POSYDON. The latter incorporates extensive grids of detailed single and binary evolution models, covering the entire evolution of a double compact object progenitor. We explore the evolution of NSBHs originating from different formation channels, which in some cases differ from earlier studies performed with rapid binary population synthesis codes. Then, we present the population properties of merging NSBH systems and their progenitors such as component masses, orbital features, and BH spins, and investigate the model uncertainties in our treatment of common envelope (CE) evolution and core-collapse process. We find that at solar metallicity, under the default model assumptions, most of the merging NSBHs have BH masses in a range of $3-11\,M{_\odot}$ and chirp masses within $1.5-4\,M{_\odot}$. Independently of our model variations, the BH always forms first with dimensionless spin parameter $\lesssim 0.2$, which is correlated to the initial binary orbital period. Some BHs can subsequently spin up moderately ($χ_{\rm BH} \lesssim 0.4$) due to mass transfer, which we assume to be Eddington limited. Binaries that experienced CE evolution rarely demonstrate large tilt angles. Conversely, approximately $40\%$ of the binaries that undergo only stable mass transfer without CE evolution contain an anti-aligned BH. Finally, accounting for uncertainties in both the population modeling and the NS equation of state, we find that $0-18.6\%$ of NSBH mergers may be accompanied by an electromagnetic counterpart.

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arXiv2023

Investigating the Lower Mass Gap with Low Mass X-ray Binary Population Synthesis

Mass measurements from low-mass black hole X-ray binaries (LMXBs) and radio pulsars have been used to identify a gap between the most massive neutron stars (NSs) and the least massive black holes (BHs). BH mass measurements in LMXBs are typically only possible for transient systems: outburst periods enable detection via all-sky X-ray monitors, while quiescent periods enable radial-velocity measurements of the low-mass donor. We quantitatively study selection biases due to the requirement of transient behavior for BH mass measurements. Using rapid population synthesis simulations (COSMIC), detailed binary stellar-evolution models (MESA), and the disk instability model of transient behavior, we demonstrate that transient-LMXB selection effects introduce observational biases, and can suppress mass-gap BHs in the observed sample. However, we find a population of transient LMXBs with mass-gap BHs form through accretion-induced collapse of a NS during the LMXB phase, which is inconsistent with observations. These results are robust against variations of binary evolution prescriptions. The significance of this accretion-induced collapse population depends upon the maximum NS birth mass $M_\mathrm{ NS, birth-max}$. To reflect the observed dearth of low-mass BHs, COSMIC and MESA models favor $M_\mathrm{ NS, birth-max} \lesssim2M_{\odot}$. In the absence of further observational biases against LMXBs with mass-gap BHs, our results indicate the need for additional physics connected to the modeling of LMXB formation and evolution.

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arXiv2023

A Black Hole Kicked At Birth: MAXI J1305-704

When a compact object is formed in a binary, any mass lost during core collapse will impart a kick on the binary's center of mass. Asymmetries in this mass loss or neutrino emission would impart an additional natal kick on the remnant black hole or neutron star, whether it was formed in a binary or in isolation. While it is well established that neutron stars receive natal kicks upon formation, it is unclear whether black holes do as well. Here, we consider the low-mass X-ray binary MAXI J1305-704, which has been reported to have a space velocity $\gtrsim$ 200 km/s. In addition to integrating its trajectory to infer its velocity upon formation of its black hole, we account for recent estimates of its period, black hole mass, mass ratio, and donor effective temperature from photometric and spectroscopic observations. We find that if MAXI J1305-704 formed via isolated binary evolution in the thick Galactic disk, then the supernova that formed its black hole imparted a natal kick of at least 70 km/s while ejecting less than $\simeq 1$ M$_\odot$ with 95% confidence assuming uninformative priors on mass loss and natal kick velocity.

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arXiv2023

X-ray luminosity function of high-mass X-ray binaries: Studying the signatures of different physical processes using detailed binary evolution calculations

The ever-expanding observational sample of X-ray binaries (XRBs) makes them excellent laboratories for constraining binary evolution theory. Such constraints can be obtained by studying the effects of various physical assumptions on synthetic X-ray luminosity functions (XLFs) and comparing to observed XLFs. In this work, we focus on high-mass XRBs (HMXBs) and study the effects on the XLF of various, poorly-constrained assumptions regarding physical processes such as the common-envelope phase, the core-collapse, and wind-fed accretion. We use the new binary population synthesis code POSYDON, which employs extensive pre-computed grids of detailed stellar structure and binary evolution models, to simulate the evolution of binaries. We generate 96 synthetic XRB populations corresponding to different combinations of model assumptions. The generated HMXB XLFs are feature-rich, deviating from the commonly assumed single-power law. We find a break in our synthetic XLF at luminosity $\sim 10^{38}$ erg s$^{-1}$, similar to observed XLFs. However, we find also a general overabundance of XRBs (up to a factor of $\sim$10 for certain model parameter combinations) driven primarily by XRBs with black hole accretors. Assumptions about the transient behavior of Be-XRBs, asymmetric supernova kicks, and common-envelope physics can significantly affect the shape and normalization of our synthetic XLFs. We find that less well-studied assumptions regarding the circularization of the orbit at the onset of Roche-lobe overflow and criteria for the formation of an X-ray emitting accretion disk around wind-accreting black holes can also impact our synthetic XLFs. Our study reveals the importance of large-scale parameter studies, highlighting the power of XRBs in constraining binary evolution theory.

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arXiv2023

The hydrodynamic evolution of binary black holes embedded within the vertically stratified disks of active galactic nuclei

Stellar-mass black holes can become embedded within the gaseous disks of active galactic nuclei (AGNs). Afterwards, their interactions are mediated by their gaseous surroundings. In this work, we study the evolution of stellar-mass binary black holes (BBHs) embedded within AGN disks using a combination of three-dimensional hydrodynamic simulations and analytic methods, focusing on environments in which the AGN disk scale height $H$ is $\gtrsim$ the BBH sphere of influence. We model the local surroundings of the embedded BBHs using a wind tunnel formalism and characterize different accretion regimes based on the local properties of the disk, which range from wind-dominated to quasi-spherical. We use our simulations to develop prescriptions for mass accretion and drag for embedded BBHs. We use these prescriptions, along with AGN disk models that can represent the Toomre-unstable outer regions of AGN disks, to study the long-term evolution of the BBHs as they migrate through the disk. We find that BBHs typically merge within $\lesssim 5-30\,{\rm Myr}$, increasing their mass significantly in the process, allowing BBHs to enter (or cross) the pair-instability supernova mass gap. The rate at which gas is supplied to these BBHs often exceeds the Eddington limit, sometimes by several orders of magnitude. We conclude that most embedded BBHs will merge before migrating significantly in the disk. Depending on the conditions of the ambient gas and the distance to the system, LISA can detect the transition between the gas-dominated and gravitational wave dominated regime for inspiraling BBHs that are formed sufficiently close to the AGN ($\lesssim$ 0.1 pc). We also discuss possible electromagnetic signatures during and following the inspiral, finding that it is generally unlikely but not inconceivable for the bolometric luminosity of the BBH to exceed that of the host AGN.

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arXiv2023

Direct Statistical Constraints on the Natal Kick velocity of a Black Hole in an X-ray Quiet Binary

In recent years, a handful of ``dark" binaries have been discovered with a non-luminous compact object. Astrometry and radial velocity measurements of the bright companion allow us to measure the post-supernova orbital elements of such a binary. In this paper, we develop a statistical formalism to use such measurements to infer the pre-supernova orbital elements, and the natal kick imparted by the supernova (SN). We apply this formalism to the recent discovery of an X-ray quiet binary with a black hole, VFTS 243, in the Large Magellanic Cloud. Assuming an isotropic, Maxwellian distribution on natal kicks and using broad agnostic mass priors, we find that kick velocity can be constrained to $V_k < 72$ km/s and the dispersion of the kick distribution to $σ_k < 68 $ km/s at 90 % confidence. We find that a Blaauw kick cannot be ruled out and }that at least about $0.6 M_{\odot}$ was lost during the supernova with 90 % confidence. The pre-SN orbital separation is found to be robustly constrained to be around $0.3$ AU.

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arXiv2022

The formation of $30\,M_\odot$ merging black holes at solar metallicity

The maximum mass of black holes formed in isolated binaries is determined by stellar winds and the interactions between the binary components. We consider for the first time fully self-consistent detailed stellar structure and binary evolution calculations in population-synthesis models and a new, qualitatively different picture emerges for the formation of black-hole binaries, compared to studies employing rapid population synthesis models. We find merging binary black holes can form with a non-negligible rate ($\sim 4\times10^{-7}\,M_\odot^{-1}$) at solar metallicity. Their progenitor stars with initial masses $\gtrsim 50\,M_\odot$ do not expand to supergiant radii, mostly avoiding significant dust-driven or luminous blue variable winds. Overall, the progenitor stars lose less mass in stellar winds, resulting in black holes as massive as $\sim 30\,M_\odot$, and, approximately half of them avoid a mass-transfer episode before forming the first-born black hole. Finally, binaries with initial periods of a few days, some of which may undergo episodes of Roche-lobe overflow mass transfer, result in mildly spinning first-born black holes, $χ_\mathrm{BH1} \lesssim 0.2$, assuming efficient angular-momentum transport.

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arXiv2022

Active Learning for Computationally Efficient Distribution of Binary Evolution Simulations

Binary stars undergo a variety of interactions and evolutionary phases, critical for predicting and explaining observed properties. Binary population synthesis with full stellar-structure and evolution simulations are computationally expensive requiring a large number of mass-transfer sequences. The recently developed binary population synthesis code POSYDON incorporates grids of MESA binary star simulations which are then interpolated to model large-scale populations of massive binaries. The traditional method of computing a high-density rectilinear grid of simulations is not scalable for higher-dimension grids, accounting for a range of metallicities, rotation, and eccentricity. We present a new active learning algorithm, psy-cris, which uses machine learning in the data-gathering process to adaptively and iteratively select targeted simulations to run, resulting in a custom, high-performance training set. We test psy-cris on a toy problem and find the resulting training sets require fewer simulations for accurate classification and regression than either regular or randomly sampled grids. We further apply psy-cris to the target problem of building a dynamic grid of MESA simulations, and we demonstrate that, even without fine tuning, a simulation set of only $\sim 1/4$ the size of a rectilinear grid is sufficient to achieve the same classification accuracy. We anticipate further gains when algorithmic parameters are optimized for the targeted application. We find that optimizing for classification only may lead to performance losses in regression, and vice versa. Lowering the computational cost of producing grids will enable future versions of POSYDON to cover more input parameters while preserving interpolation accuracies.

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