Bulletin of the American Physical Society
APS April Meeting 2020
Volume 65, Number 2
Saturday–Tuesday, April 18–21, 2020; Washington D.C.
Session J09: Gravitational Wave PopulationsLive
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Sponsoring Units: DAP DGRAV Chair: Tyson Littenberg, Marshall Space Flight Center Room: Roosevelt 4 |
Sunday, April 19, 2020 1:30PM - 1:42PM Live |
J09.00001: Binary black hole merger rates in rapid population-synthesis codes and the impact of improved modeling of binary physics Monica Gallegos-Garcia, Kaliroë Pappas, Pablo Marchant, Christopher Berry, Vicky Kalogera Rapid binary population synthesis codes have been used for decades to investigate the complex evolution of compact binaries. Although these codes are widely used, they typically lack thorough calculations and prescriptions of physical processes (e.g., common-envelope, roche lobe overflow, post main-sequence evolution). These are crucial to accurately predict the fate of binary systems. Many of these processes, however, have been more carefully implemented in stellar evolution codes such as MESA (Modules for Experiments in Stellar Astrophysics). Motivated by this, we perform binary evolution simulations to compare results between a fast binary population synthesis code, COSMIC, and MESA. We find that COSMIC produces more merging binary black holes compared to MESA, indicating that current predictions from binary population synthesis codes may be overestimates for the number of binary black holes formed via isolated field evolution. Understanding the origin of compact object binaries, and having robust predictions for binary merger rates, is critical for interpreting the growing catalog of gravitational-wave observations. [Preview Abstract] |
Sunday, April 19, 2020 1:42PM - 1:54PM Live |
J09.00002: Relativistic Three-body Effects in Hierarchical Triples Halston Lim, Carl Rodriguez The hierarchical three-body problem has many applications in relativistic astrophysics, and is very likely to play an important role in forming binary black hole mergers detected by LIGO/Virgo. However, the majority of studies have only included relativistic corrections to the two-body equations of motion, and have ignored the relativistic effects that arise in the presence of a third body. We revisit this problem and develop a fully consistent derivation of the secular three-body problem to first post-Newtonian order. We perform a post-Keplerian, two-parameter expansion of the single orbit-averaged Lagrange planetary equations in $\delta=v^2/c^2$ and $\epsilon=a_1/a_2$, where $a_1$ and $a_2$ are the semi-major axes of the inner and outer orbit, respectively. It is well established that eccentricity growth through the Lidov-Kozai mechanism can be suppressed or amplified by two-body 1pN precession. In this study, we derive and investigate three-body 1pN effects and find that these effects lead to heightened eccentricity growth in triples in certain regions of parameter space. In such cases, inclusion of these effects can substantially alter the evolution of three-body systems as compared to an analysis in which they are neglected. [Preview Abstract] |
Sunday, April 19, 2020 1:54PM - 2:06PM Live |
J09.00003: Black Hole Coagulation: Modeling Hierarchical Mergers in Black Hole Populations Zoheyr Doctor, Daniel Wysocki, Richard O'Shaughnessy, Daniel Holz, Ben Farr Data from the LIGO and Virgo detectors has confirmed that stellar-mass black holes can merge within a Hubble time, leaving behind massive remnant black holes. In some astrophysical environments such as globular clusters and AGN disks, it may be possible for these remnants to take part in further compact-object mergers, producing a population of hierarchically formed black holes. In this work, we present a parameterized framework for describing the population of binary black hole mergers, while self-consistently accounting for hierarchical mergers. The framework casts black holes as particles in a box which can collide based on an effective cross-section, but allows inputs from more detailed astrophysical simulations. Our approach is relevant to any population which is comprised of second or higher generation black holes, such as primordial black holes or dense cluster environments. We describe some possible inputs to this generic model and their effects on the black hole merger populations, and use the model to perform Bayesian inference on the catalog of black holes from LIGO and Virgo's first two observing runs. We find that models with a high rate of hierarchical mergers are disfavored, consistent with previous population analyses. [Preview Abstract] |
Sunday, April 19, 2020 2:06PM - 2:18PM Live |
J09.00004: Highly Spinning and Misaligned Binary Black Holes from the Isolated Formation Channel Nathan Steinle, Michael Kesden Observations of gravitational waves can constrain binary black-hole (BBH) spins. If BBHs arise from isolated binary evolution, their spins are determined by phenomena such as tides, winds, accretion, common envelope (CE), supernova (SN) kicks, and stellar core-envelope coupling. Modelling the spin evolution of a binary star until it forms a BBH involves the complicated interplay of these phenomena. For a few physically motivated scenarios, we parameterize binary stellar evolution to identify regions of the parameter space which form BBHs that merge within the age of the Universe with large spins misaligned with the orbital angular momentum. In our model, a BH can be highly spinning ($\rchi \gtrsim 0.5$) if either: (1) its Wolf-Rayet (WR) progenitor evolved from a star that had weak core-envelope coupling and provided an initial spin of at least 10\% of the WR breakup value, (2) tides spin up the WR progenitor following the CE phase, or (3) accretion onto the WR progenitor or BH increase the spin. BBH spins can be highly misaligned ($\cos(\theta) \lesssim 0.7$) if the SN kicks are comparable to the orbital velocity which depends on whether the SN kicks occur before or after the CE phase, and tides or accretion fail to realign the spins. [Preview Abstract] |
Sunday, April 19, 2020 2:18PM - 2:30PM Live |
J09.00005: Measuring the Peak of the Binary Black Hole Redshift Distribution Thomas Callister, Maya Fishbach, Daniel Holz, Will Farr A prime target of gravitational-wave astronomy is to understand the evolution of the binary black hole merger rate with redshift. If measured, the redshift distribution of binary black holes would provide substantial insight into their life cycle, encoding the characteristic time delay between binary formation and merger, the dependence of black hole formation on stellar metallicity, and perhaps even the relative contributions from competing binary formation channels. Currently, such studies are limited by the range of existing instruments. Advanced LIGO and Virgo can observe compact binaries only out to redshift $z\sim 1$, whereas the binary black hole merger rate is expected to peak at $z\sim 2$ or beyond. We do, however, have an alternate means of measuring the rate of high-redshift mergers — the astrophysical gravitational-wave background. In this talk, I will demonstrate how the synthesis of direct detections at low redshift with existing limits on the gravitational-wave background enables powerful new constraints on the high-redshift evolution of the binary black hole merger rate. Using this technique, Advanced LIGO and Virgo may soon be able to measure the rise, peak, and even subsequent turnover of the binary black hole redshift distribution. [Preview Abstract] |
Sunday, April 19, 2020 2:30PM - 2:42PM Live |
J09.00006: Distinguishing high-mass binary neutron stars from binary black holes Nathan Johnson-McDaniel, An Chen, Tim Dietrich, Reetika Dudi Advanced LIGO and Advanced Virgo are expected to detect tens of binary neutron stars (BNSs) in upcoming observing runs, and third-generation gravitational wave detectors are expected to detect many more. While the BNS merger that produced GW170817 led to a wide variety of electromagnetic counterparts, some of the BNSs detected in the future are expected to have a large enough total mass that they will collapse directly to a black hole when they merge. In such cases, little to no matter remains outside the final black hole to power electromagnetic counterparts. GW190425 may be an example of such a system. Thus, for these systems, the imprint of the neutron stars’ material nature on the gravitational waveform (e.g., through tidal deformations) will be the only way to distinguish them from low-mass binary black holes (BBHs). To predict how easy it will be to distinguish high-mass BNSs from low-mass BBHs with current and future gravitational wave detectors, we perform parameter estimation on injections of hybrid effective-one-body/numerical relativity BNS and BBH waveforms and consider the constraints on masses and tidal deformabilities. We find that it should be possible to distinguish some BNSs undergoing prompt collapse from BBHs with high confidence even with an O4-like network. [Preview Abstract] |
Sunday, April 19, 2020 2:42PM - 2:54PM Live |
J09.00007: Machine learning in gravitational wave population analysis Wang Kei Wong, Shirley Ho, Emanuele Berti The growing catalog of stellar-mass compact binary systems detected in gravitational waves offers burgeoning insights to physics governing their evolution. At the same time its increasing complexity poses a more significant challenge to our data analysis techniques. We review some recent developments on incorporating machine learning techniques in analyzing gravitational-wave catalogs. We also present a new machine to perform population analysis. By incorporating a flow-based deep generative network into a hierarchical Bayesian framework, one can handle astrophysical models of compact binaries that have higher dimensions and complexity as compared to previous studies, with greater accuracy and efficiency. This new machine offers novel and unique opportunities to directly constrain various astrophysical model with gravitational-wave observations. [Preview Abstract] |
Sunday, April 19, 2020 2:54PM - 3:06PM |
J09.00008: Properties of Select Compact Object Merger from the Advanced LIGO-Virgo Observing Run O3a and Relevant Astrophysics Implications Charlie Hoy The Advanced LIGO and Virgo gravitational-wave detectors began their third observing run in April 2019. The improved sensitivity of the instruments led to a significant increase in the rate of detections, as well as the potential to explore new regions of the binary-merger parameter space. We present the physical properties of a novel event which was discovered during the first six months of O3 and we discuss the relevant astrophysical implications. [Preview Abstract] |
Sunday, April 19, 2020 3:06PM - 3:18PM Not Participating |
J09.00009: Phenomenologically reconstructing properties of multiple compact binary merger populations: the small-$N$ limit Daniel Wysocki, Richard O'Shaughnessy The LIGO and Virgo gravitational wave (GW) observatories have detected both binary black hole (BBH) and binary neutron star (BNS) mergers, with the potential to detect neutron star--black hole (NSBH) mergers as well. Based on expected masses for black holes and neutron stars, the majority of these signals fall clearly into one of these three source categories. In this case, the three source populations can be constrained independently, considering only sources from that category. Some sources may have ambiguous classification, e.g., because GW observations often poorly constrain the binary's mass ratio, as was recently demonstrated by GW190425. Conversely, mergers may lie inside previously-anticipated mass gaps, both at high mass (above the pair instability gap) and at low mass (between BH and NS). Thus, we must in principle consider detections from all source categories simultaneously, when trying to measure the properties of any one category's population properties. In this work, we demonstrate phenomenological modeling of the combined BBH+BNS+NSBH population. We investigate the measurability of mass gaps between source categories. We also demonstrate some of the biases that can arise when attempting to only consider a single source category at a time. [Preview Abstract] |
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