Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session D16: Simulations of Black Holes, Neutron Stars, and Accretion DisksRecordings Available

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Sponsoring Units: DGRAV DAP Chair: Michal Pirog, West Virginia University Room: Marquis C 
Saturday, April 9, 2022 1:30PM  1:42PM 
D16.00001: The Impact of Stellar Compactness on Black Hole  Neutron Star Binary Mergers Pablo Laguna, Miguel GraciaLinares, Bhavesh Khamesra Stellar disruption in black hole  neutron star mergers depends on the spin of the black hole, the mass ration of the system, and the compactness of the neutron star via its equation of state. In a previous study, we investiagted the effects of the stellar disruption on the gravitational wave emission as a function of the mass ratio for a stellar model with constant compactness. In the present study, we extend the study to investigate the effects from varying the compactness, paying attention to not only the gravitational wave emission but also to the dynamics of the apparent horizon of the black hole and its kick after the merger. 
Saturday, April 9, 2022 1:42PM  1:54PM 
D16.00002: Highaccuracy waveforms for black holeneutron star systems Tia K Martineau, Francois V Foucart The observation of gravitational waves (GWs) relies on accurate analytical waveform models. These models are also necessary for parameter estimation of the two astronomical bodies that comprise compact binaries. The production of such analytical waveform models for GW astrophysics depends on whether or not accurate numerical waveforms are available for public use. For black holeneutron star (BHNS) merger events, there is an absence of publicly available accurate numerical waveforms. The increase in the sensitivity of GW interferometers will inevitably bring about additional detections of BHNS binary merger events. In this talk, I summarize a number of long, accurate numerical BHNS waveforms produced via the spectral Einstein code (SpEC) to better span the binary parameter space of potential BHNS merger configurations. These waveforms are publicly available as part of the Simulating eXtreme Spacetimes (SxS) collaboration’s catalog. 
Saturday, April 9, 2022 1:54PM  2:06PM 
D16.00003: Relativistic effects on neutron star fundamentalmode dynamical tides Sizheng Ma, Tanja Hinderer, Jan Steinhoff, Francois V Foucart During the final stage of the coalescence of a black holeneutron star system, the tidal excitation of the quasinormal modes of the neutron star can leave significant imprints on gravitational waves. Understanding this process and building a robust theoretical model is important for extracting neutron star properties from gravitationalwave data. In this talk, we will discuss how the quasinormal modes of the neutron star in the binary environment are modified by relativistic effects, including the gravitational redshift and the framedragging due to the spin on the black hole. We investigate the impact of these two relativistic effects on gravitational waves by incorporating them in the SEOBNRv4T waveform model. We compare this new model with a few new black holeneutron star simulations that are performed using a numerical relativity code Spectral Einstein Code. 
Saturday, April 9, 2022 2:06PM  2:18PM 
D16.00004: Tabulated equation of state support within IllinoisGRMHD Pedro Espino, Gabriele Bozzola, Vasileios Paschalidis Presently, the best tools for understanding BNS mergers in their most extreme stages are detailed general relativistic magnetohydrodynamic (GRMHD) simulations. Although recent years have seen the development and improvement of accurate GRMHD codes, only a few of these are opensource. Among these is the widely used IllinoisGRMHD code, which in its present opensource state lacks the ability to simulate fluids with the use of multidimensional, finite temperature equation of state tables. We present new developments to IllinoisGRMHD which allow for its use with realistic, finite temperature equations of state. Our adaptation of the code includes advection of the electron fraction, which is crucial in understanding the nucleosynthetic processes associated with BNS mergers, and new conservativetoprimitive recovery routines which are based on modern solution algorithms. We discuss stringent tests of our version of IllinoisGRMHD and present detailed comparisons to other opensource GRMHD codes. We consider the evolution and amplification of magnetic fields in BNS systems described using finite temperature equations of state to showcase the full capability of our code. We find that our version of IllinoisGRMHD behaves as expected, and similar to other opensource GRMHD codes, when considering many systems of astrophysical interest. 
Saturday, April 9, 2022 2:18PM  2:30PM 
D16.00005: Smooth spectral equations of state in binary neutron star merger simulations with SpEC Alexander Knight Gravitational waves emitted from binary neutron star merger events can carry information about the total mass, orbital frequency, mass ratio, and compactness of the system and the stars. To reliably extract these parameters from gravitational wave observations, we need analytical waveform models calibrated to the results of highaccuracy simulations of merging binaries. However, in the Spectral Einstein Code (SpEC), highorder convergence of the simulated gravitational waveform requires smooth evolution variables, whereas most commonly used equations of state are either overly simplified or have discontinuities in the pressure function, resulting in increased errors and lowerorder convergence. In this talk, we will present our results, errors, and analysis of a smooth, spectral equation of state using a series of simulations with a constant chirp mass, and varying mass ratios and resolutions. 
Saturday, April 9, 2022 2:30PM  2:42PM 
D16.00006: Simulating a magnetized neutron star with discontinuous Galerkin methods Nils Deppe, Lawrence E Kidder, Saul Teukolsky, Francois Hebert We present a brief overview of our finitedifferencediscontinuous Galerkin 
Saturday, April 9, 2022 2:42PM  2:54PM 
D16.00007: Comparison of shock capturing schemes for the discontinuous Galerkin method in GRMHD Yoonsoo Kim, Nils Deppe, Francois Hebert, William T Throwe, Lawrence E Kidder, Mark A Scheel, Saul Teukolsky Using our opensource code SpECTRE, we present a detailed comparison of various limiting and shock capturing strategies for the discontinuous Galerkin methods proposed in the literature applied to a set of test problems in general relativistic magnetohydrodynamics (GRMHD). We compare the standard minmod/ΛΠN limiter, the hierarchical limiter of Krivodonova, the simple WENO limiter, the HWENO limiter, and a discontinuous Galerkinfinite difference hybrid method. The goal is to evaluate the robustness and accuracy of the different strategies in order to understand which are most likely able to simulate neutron stars. 
Saturday, April 9, 2022 2:54PM  3:06PM 
D16.00008: Evolution of a magnetized accretion disk using SpECTRE William T Throwe A primary goal of the opensource SpECTRE project is to simulate the disruption of neutron stars in compactobject binary systems. As a step towards this goal, we present the evolution of a relativistic magnetized accretion disk in a fixed gravitational field. The evolution uses a hybrid scheme of a discontinuous Galerkin method with embedded finitedifference regions for shock capturing. 
Saturday, April 9, 2022 3:06PM  3:18PM 
D16.00009: Can ThorneZytkow objects source GW190814 type events? David Garfinkle, Ilias Cholis, Konstantinos Kritos We consider scenarios where a mass gap black hole is formed as the end state of a ThorneZytkow object: a red giant with a neutron star in its core. We estimate the rate for such mass gap objects to subsequently merge with a black hole. 
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