Authors: Simone S. Bavera, Tassos Fragos, Emmanouil Zapartas, Jeff J. Andrews, Vicky Kalogera, Christopher P. L. Berry, Matthias Kruckow, Aaron Dotter, Konstantinos Kovlakas, Devina Misra, Kyle A. Rocha, Philipp M. Srivastava, Meng Sun, Zepei Xing

Access: arXiv:2212.10924 || NASA ADS || INSPIRE-HEP

Abstract: 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 (∼4×10−7M−1⊙) at solar metallicity. Their progenitor stars with initial masses ≳50M⊙ 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 ∼30M⊙, 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, χBH1≲0.2, assuming efficient angular-momentum transport.

Authors: Chase Kimball, Sam Imperato, Vicky Kalogera, Kyle A. Rocha, Zoheyr Doctor, Jeff J. Andrews, Aaron Dotter, Emmanouil Zapartas, Simone S. Bavera, Konstantinos Kovlakas, Tassos Fragos, Phillip M. Srivastava, Devina Misra, Meng Sun, Zepei Xing

Access: arXiv:2211.02158 || NASA ADS || INSPIRE-HEP

Abstract: 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 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 ࣡ 200 km/s. In addition to integrating its trajectory to infer its velocity upon formation of its black hole, we reconstruct its evolutionary history, accounting 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 its black hole received a natal kick of at least 70 km/s with 95% confidence.

Authors: Jared C. Siegel, Ilia Kiato, Vicky Kalogera, Christopher P. L. Berry, Thomas J. Maccarone, Katelyn Breivik, Jeff J. Andrews, Simone S. Bavera, Aaron Dotter, Tassos Fragos, Konstantinos Kovlakas, Devina Misra, Kyle A. Rocha, Philipp M. Srivastava, Meng Sun, Zepei Xing, Emmanouil Zapartas

Access: arXiv:2209.06844 || NASA ADS || INSPIRE-HEP

Abstract: 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 (NS) and the least massive black holes (BH). 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 present the first quantitative study of 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 do introduce biases into the observed sample. If a gap is not inherent in BH birth masses, mass growth through LMXB accretion and selection effects can suppress mass-gap BHs in the observed sample. Our results are robust against variations of binary evolution prescriptions. We further find that a population of transient LMXBs with mass-gap BHs form through accretion induced collapse of a NS during the LMXB phase. The significance of this population is dependent on the maximum NS birth mass M_{NS,birth−max}. For M_{NS,birth−max}=3M_⊙, MESA and COSMIC models predict a similar fraction of mass gap LMXBs. However, for M_{NS,birth−max} ≾ 2M_⊙ and realistic models of the disk-instability, our MESA models produce a dearth of mass-gap LMXBs, more consistent with observations. This constraint on M_{NS,birth−max} is independent of whether low-mass BHs form at core-collapse.

Authors: Devina Misra, Konstantinos Kovlakas, Tassos Fragos, Margaret Lazzarini, Simone S. Bavera, Bret D. Lehmer, Andreas Zezas, Emmanouil Zapartas, Zepei Xing, Jeff J. Andrews, Aaron Dotter, Kyle A. Rocha, Philipp M. Srivastava, Meng Sun

Access: arXiv:2209.05505 || NASA ADS || INSPIRE-HEP

Abstract: The ever-expanding observational sample of X-ray binaries (XRBs) makes them excellent laboratories for constraining binary evolution theory. Useful insights can be obtained by studying the effects of various physical assumptions on synthetic X-ray luminosity functions (XLFs) and comparing with observed XLFs. 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 and generate 96 synthetic XRB populations corresponding to different combinations of model assumptions. The generated XLFs are feature-rich, deviating from the commonly assumed single power law. We find a break in our synthetic XLF at luminosity ~ 10³⁸ erg/s, similarly to observed XLFs. However, we find also a general overabundance of XRBs (up to a factor of ~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 orbit circularization at the onset of Roche-lobe overflow and criteria for the formation of a wind-fed X-ray emitting accretion disk around black holes can also impact our synthetic XLFs and reduce the discrepancy with observations. Due to model uncertainties, our synthetic XLFs do not always agree well with observations. However, different combinations of model parameters leave distinct imprints on the shape of the synthetic XLFs and can reduce this deviation, revealing the importance of large-scale parameter studies and highlighting the power of XRBs in constraining binary evolution theory.

Authors: Kyle Akira Rocha, Jeff J. Andrews, Christopher P. L. Berry, Zoheyr Doctor, Pablo Marchant, Vicky Kalogera, Scott Coughlin, Simone S. Bavera, Aaron Dotter, Tassos Fragos, Konstantinos Kovlakas, Devina Misra, Zepei Xing, Emmanouil Zapartas

Access: arXiv:2203.16683 || NASA ADS || INSPIRE-HEP || Journal

Abstract: 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 ∼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.

Authors: Tassos Fragos, Jeff J. Andrews, Simone S. Bavera, Christopher P. L. Berry, Scott Coughlin, Aaron Dotter, Prabin Giri, Vicky Kalogera, Aggelos Katsaggelos, Konstantinos Kovlakas, Shamal Lalvani, Devina Misra, Philipp M. Srivastava, Ying Qin, Kyle A. Rocha, Jaime Román-Garza, Juan Gabriel Serra, Petter Stahle, Meng Sun, Xu Teng, Goce Trajcevski, Nam Hai Tran, Zepei Xing, Emmanouil Zapartas, Michael Zevin

Access: arXiv:2202.05892 || NASA ADS || INSPIRE-HEP || Journal || Code release

Abstract: 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.

Authors: Xu Teng, Thomas Beckler, Bradley Gannon, Benjamin Huinker, Gabriel Huinker, Koushhik Kumar, Christina Marquez, Jacob Spooner, Goce Trajcevski, Prabin Giri, Aaron Dotter, Jeff Andrews, Scott Coughlin, Ying Qin, Juan Gabriel Serra-Pérez, Nam Tran, Jaime Román-Garja, Konstantinos Kovlakas, Emmanouil Zapartas, Simone Bavera, Devina Misra, Tassos Fragos

Access: ACM DIGITAL LIBRARY

Abstract: Traditionally, clustering of multivariate data aims at grouping objects described with multiple heterogeneous attributes based on a suitable similarity (conversely, distance) function. One of the main challenges is due to the fact that it is not straightforward to directly apply mathematical operations (e.g., sum, average) to the feature values, as they stem from heterogeneous contexts. In this work we take the challenge a step further and tackle the problem of clustering multivariate datasets based on jointly considering: (a) similarity among a subset of the attributes; and (b) distance-based diversity among another subset of the attributes. Specifically, we focus on astrophysics data, where the snapshots of the stellar evolution for different stars contain over 40 distinct attributes corresponding to various physical and categorical (e.g., 'black hole') attributes. We present CSD-CAMD -- a prototype system for Coupling Similarity and Diversity for Clustering Astrophysics Multivariate Datasets. It provides a flexibility for the users to select their preferred subsets of attributes; assign weight (to reflect their relative importance on the clustering); and select whether the impact should be in terms of proximity or distance. In addition, CSD-CAMD allows for selecting a clustring algorithm and enables visualization of the outcome of clustering.

Authors: Xu Teng, Adam Corpstein, Joel Holm, Willis Knox, Becker Mathie, Philip Payne, Ethan Vander Wiel, Prabin Giri, Goce Trajcevski, Aaron Dotter, Jeff Andrews, Scott Coughlin, Ying Qin, Juan Gabriel Serra-Pérez, Nam Tran, Jaime Román-Garja, Konstantinos Kovlakas, Emmanouil Zapartas, Simone Bavera, Devina Misra, Tassos Fragos

Access: ACM DIGITAL LIBRARY

Abstract: We present CACSE – a system for Context Aware Clustering of Stellar Evolution – for datasets corresponding to temporal evolution of stars, which are multivariate time series, usually with a large number of attributes (e.g., ≥ 40). Typically, the datasets are obtained by simulation and are relatively large in size (5 ∼ 10 GB per certain interval of values for various initial conditions). Investigating common evolutionary trends in these datasets often depends on the context – i.e., not all the attributes are always of interest, and among the subset of the context-relevant attributes, some may have more impact than others. To enable such context-aware clustering, our CACSE system provides functionalities allowing the domain experts to dynamically select attributes that matter, and assign desired weights/priorities. Our system consists of a PostgreSQL database, Python-based middleware with RESTful and Django framework, and a web-based user interface as frontend. The user interface provides multiple interactive options, including selection of datasets and preferred attributes along with the corresponding weights. Subsequently, the users can select a time instant or a time range to visualize the formed clusters. Thus, CACSE enables a detection of changes in the the set of clusters (i.e., convoys) of stellar evolution tracks. Current version provides two of the most popular clustering algorithms – k-means and DBSCAN.

Authors: Simone S. Bavera, Tassos Fragos, Emmanouil Zapartas, Enrico Ramirez-Ruiz, Pablo Marchant, Luke Z. Kelley, Michael Zevin, Jeff Andrews, Scotty Coughlin, Aaron Dotter, Konstantinos Kovlakas, Devina Misra, Juan Gabriel Serra-Pérez, Ying Qin, Kyle A. Rocha, Jaime Román-Garza, Nam Hai Tran, Zepei Xing

Access: arXiv:2106.15841 || NASA ADS || INSPIRE-HEP || Journal

Abstract: Long gamma-ray bursts are associated with the core-collapse of massive, rapidly spinning stars. However, the believed efficient angular momentum transport in stellar interiors 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, with rates matching the empirical ones. We find that ≈10% of the GWTC-2 reported binary black holes had a long gamma-ray burst associated with their formation, with GW190517 and GW190719 having a probability of ≈85% and ≈60%, respectively, being among them.

Authors: Emmanouil Zapartas, Mathieu Renzo, Tassos Fragos, Aaron Dotter, Jeff Andrews, Simone S. Bavera, Scotty Coughlin, Devina Misra, Konstantinos Kovlakas, Jaime Román-Garza, Juan Gabriel Serra-Pérez, Ying Qin, Kyle A. Rocha, Nam Hai Tran

Access: arXiv:2106.05228 || NASA ADS || INSPIRE-HEP || Journal

Abstract: Stripped-envelope supernovae (Type IIb, Ib, Ic) showing little or no hydrogen are one of the main classes of explosions of massive stars. Their origin and the evolution of their progenitors are not fully understood as yet. Very massive single stars stripped by their own winds (≳25 - 30M_⊙ at solar metallicity) are considered viable progenitors of these events. However, recent 1D core-collapse simulations show that some massive stars may collapse directly onto black holes after a failed explosion, with weak or no visible transient. In this letter, we estimate the effect of direct collapse onto a black hole on the rates of stripped-envelope supernovae that arise from single stars. For this, we compute single star MESA models at solar metallicity and map their final state to their core-collapse outcome following prescriptions commonly used in population synthesis. According to our models, no single stars that have lost their entire hydrogen-rich envelope are able to explode, and only a fraction of progenitors with a thin hydrogen envelope left (IIb progenitor candidates) do, unless we invoke increased wind mass-loss rates. This result increases the existing tension between the single-star scenario for stripped-envelope supernovae and their observed rates and properties. At face value, our results point towards an even higher contribution of binary progenitors for stripped-envelope supernovae. Alternatively, they may suggest inconsistencies in the common practice of mapping different stellar models to core-collapse outcomes and/or higher overall mass loss in massive stars.

Authors: Jaime Román-Garza, Simone S. Bavera, Tassos Fragos, Emmanouil Zapartas, Devina Misra, Jeff Andrews, Scotty Coughlin, Aaron Dotter, Konstantinos Kovlakas, Juan Gabriel Serra-Pérez, Ying Qin, Kyle A. Rocha, Nam Hai Tran

Access: arXiv:2012.02274 || NASA ADS || INSPIRE-HEP || Journal

Abstract: Recent detailed 1D core-collapse simulations have brought new insights on the final fate of massive stars, which are in contrast to commonly used parametric prescriptions. In this work, we explore the implications of these results to the formation of coalescing black-hole (BH) - neutron-star (NS) binaries, such as the candidate event GW190426_152155 reported in GWTC-2. Furthermore, we investigate the effects of natal kicks and the NS's radius on the synthesis of such systems and potential electromagnetic counterparts linked to them. Synthetic models based on detailed core-collapse simulations result in an increased merger detection rate of BH-NS systems (~2.3 yr^-1), 5 to 10 times larger than the predictions of "standard" parametric prescriptions. This is primarily due to the formation of low-mass BH via direct collapse, and hence no natal kicks, favored by the detailed simulations. The fraction of observed systems that will produce an electromagnetic counterpart, with the detailed supernova engine, ranges from 2-25%, depending on uncertainties in the NS equation of state. Notably, in most merging systems with electromagnetic counterparts, the NS is the first-born compact object, as long as the NS's radius is ≲12km. Furthermore, core-collapse models that predict the formation of low-mass BHs with negligible natal kicks increase the detection rate of GW190426_152155-like events to ~0.6 yr^-1; with an associated probability of electromagnetic counterpart ≤ 10% for all supernova engines. However, increasing the production of direct-collapse low-mass BHs also increases the synthesis of binary BHs, over-predicting their measured local merger density rate. In all cases, models based on detailed core-collapse simulation predict a ratio of BH-NSs to binary BHs merger rate density that is at least twice as high as other prescriptions.

Authors: Simone S. Bavera, Tassos Fragos, Michael Zevin, Christopher P. L. Berry, Pablo Marchant, Jeff J. Andrews, Scott Coughlin, Aaron Dotter, Konstantinos Kovlakas, Devina Misra, Juan G. Serra-Pérez, Ying Qin, Kyle A. Rocha, Jaime Román-Garza, Nam H. Tran, Emmanouil Zapartas

Access: arXiv:2010.16333 || NASA ADS || INSPIRE-HEP || Journal

Abstract: 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, Μ_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 ~ 2), outside current detector horizons. Assuming Eddington-limited accretion efficiency and that the first-born black hole is formed with a negligible spin, we find that all non-zero χeff systems in the detectable population can come only from the common envelope channel as the stable mass-transfer channel cannot shrink the orbits enough for efficient tidal spin-up to take place. We find the local rate density (z ≃ 0.01) for the common envelope channel is in the range ~ 17 − 113 Gpc⁻³ yr⁻¹ considering a range of α_CE ∈ [0.2,5.0] while for the stable mass transfer channel the rate density is ~ 25 Gpc⁻³ yr>⁻¹. The latter drops by two orders of magnitude if the mass accretion onto the black hole is not Eddington limited because conservative mass transfer does not shrink the orbit as efficiently as non-conservative mass transfer does. Finally, using GWTC-2 events, we constrain the lower bound of branching fraction from other formation channels in the detected population to be ~ 0.2. Assuming all remaining events to be formed through either stable mass transfer or common envelope channels, we find moderate to strong evidence in favour of models with inefficient common envelopes.