Bulletin of the American Physical Society
APS April Meeting 2020
Volume 65, Number 2
Saturday–Tuesday, April 18–21, 2020; Washington D.C.
Session L09: Neutron Star and Black Hole Binary Merger Simulations and ModelingLive

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Sponsoring Units: DAP DGRAV Chair: Andrew Macfadyen, New York University Room: Roosevelt 4 
Sunday, April 19, 2020 3:30PM  3:42PM Live 
L09.00001: GRMHD Simulations of Binary Neutron Star Mergers: 100 ms of LongLived Merger Evolution Jay Vijay Kalinani, Riccardo Ciolfi, Wolfgang Kastaun, Bruno Giacomazzo Recent multimessenger observation of the short gammaray burst (SGRB) GRB 170817A together with the gravitational wave (GW) event GW170817 provides evidence for the longstanding hypothesis associating SGRBs with binary neutron star (BNS) mergers. The nature of the remnant object powering the SGRB, which could have been either an accreting black hole (BH) or a longlived magnetized neutron star (NS), is however still uncertain. In this talk, I will present our work based on exploring the case of longlived NS as a possible SGRB jet central engine by performing a general relativistic magnetohydrodynamic BNS merger simulation extending up to about 100 milliseconds after merger, much longer than any previous simulation of this kind. In particular, I will focus on the overall merger dynamics, structure and rotation profile of the formed postmerger remnant, evolution of magnetic fields, followed by arguments based on our simulation results on jetformation by such a scenario. [Preview Abstract] 
Sunday, April 19, 2020 3:42PM  3:54PM Not Participating 
L09.00002: Numerical approach to Supermassive Black Hole Binary  Disk interactions Michal Pirog, Sean McWilliams, Siddharth Mahesh The talk will cover the recent numerical investigation of a system composed of a Supermassive Black Hole Binary and a nonselfgravitating, thin, locally isothermal, viscous disk. This work is being conducted in coordination with the recent analytical results for the gap opening criteria due to Lindblad Resonances. I will present a comprehensive description of the numerical methods, numerical code and finally the physical setup. Starting from a toy model, where the binary and the disk are coplanar, I will introduce more general configurations with the inclination angle as a free parameter. For binaries that are surrounded by a sufficiently massive circumbinary disk, we expect that the mutual torques between a binary and a disk will impact the signal observable by pulsar timing arrays. We expect the inclination angle to significantly influence the size of this torque, so that spininduced precession could also modulate any electromagnetic signal from such a binary, and therefore could help us to identify these sources with conventional telescopes. [Preview Abstract] 
Sunday, April 19, 2020 3:54PM  4:06PM 
L09.00003: Dynamical Simulations of Binary Neutron Star Mergers Tanmayee Gupte, Joshua Faber, Grace Fiacco, Trung Ha The recent detection of gravitational waves (GW) from a system of binary neutron stars (BNS) in coincidence with electromagnetic observations has launched a new era of multimessenger astrophysics. As a result, BNS mergers are one of the main targets for GW interferometer detectors on earth. A particularly interesting challenge is to constraint the equation of state (EOS) of the nuclear matter inside the neutron star core, which is still theoretically unknown. In order to do parameter estimation and detect additional GW signals, we need to compare the observed signals to theoretical GW templates, which depend on different characteristics like total mass, EOS, mass ratio, etc. Limited work has been previously done with simulating unequalmass BNS because of numerical difficulties. We have modified the LORENE code to advance our ability to construct unequalmass BNS initial data, and used them to initiate dynamical evolutions of BNS mergers performed using the Einstein Toolkit. Here we discuss our analysis of the dynamics of the merger for varying mass ratios and different EOSs represented as piecewise. We will focus on the relationship between the BNS mass ratio, EOS and the ejected mass from corresponding merger. [Preview Abstract] 
Sunday, April 19, 2020 4:06PM  4:18PM 
L09.00004: Evolution of black holeneutron star postmerger disks in axisymmetric relativistic hydrodynamics Milad Haddadi The remnant accretion disk from a black holeneutron star binary merger can be responsible for electromagnetic counterparts to a gravitational wave signal. For example, a disk is needed for a shortduration gammaray burst, and disk winds can contribute to a kilonova. Numerical relativity simulations provide the only realistic postmerger initial state, but due to the cost of 3D simulations, these usually only cover the first tens of milliseconds. We report on our recent 2D black holeneutron star postmerger disk simulations in axisymmetric relativistic hydrodynamics. We evolve the disk for a few hundred milliseconds from realistic initial data from 3D simulations. Our postmerger simulations employ an alpha viscosity model to account for angular momentum transport, and they include M1 neutrino transport for a more realistic evolution of the composition in the disk and its ejecta. [Preview Abstract] 
Sunday, April 19, 2020 4:18PM  4:30PM 
L09.00005: Gravitational Wave Identification of High MassRatio Black Hole Neutron Star Mergers Pablo Laguna, Bhavesh Khamesra, Miguel Gracia Linares, Richard Udall, Deirdre Shoemaker Depending on the compactness of the neutron star and the mass of the black hole, the coalescence of a mixed binary system would yield a disruption of the neutron star before it mergers with the black hole or a coalescence in which the neutron star is essentially swallowed by the black hole almost undisturbed. The latter case will occur for cases of high massratio. We present results of a study aimed at characterizing the ability of LIGO/VIRGO in discerning between binary black hole and mixed binary mergers when the neutron star undergoes minimal disruption. [Preview Abstract] 
Sunday, April 19, 2020 4:30PM  4:42PM 
L09.00006: Effect of Precession on Gap Clearing: An Application to Spinning SuperMassive Black Hole Binaries Siddharth Mahesh, Sean McWilliams, Michal Pirog The study of gas disks surrounding a supermassive blackhole binary (SMBHB) and their evolution during both the inspiral and merger stages can inform electromagnetic searches for candidate SMBHBs, in addition to being relevant for the expected gravitationalwave signal. A toy model for such a system involves an initial clearing of a central cavity in which the binary evolves independently from the disk dynamics. It is therefore possible in the early phases of such decoupled evolution that spinorbit induced precession can allow for periodic misalignment in the planes of the binary and circumbinary disks. This study aims to quantify the response of the cavity cleared through the mechanism of Lindblad resonances to such a misalignment. Analytical calculations of truncation radii for misaligned disks are combined with OrderofMagnitude timescale arguments to indicate the inner radius of the disk evolves secularly on the spinorbit precession timescale. Numerical follow up will clarify the effect of the secular evolution on the soft Xray spectrum, which is believed to be dominated by resonant gap clearing. [Preview Abstract] 
Sunday, April 19, 2020 4:42PM  4:54PM Not Participating 
L09.00007: Robust adaptiveorder numerical methods for relativistic magnetohydrodynamics Nils Deppe We present a new positivitypreserving adaptiveorder method that combines discontinuous Galerkin and finitedifference schemes in a way that ensures physical realizability of the solution (e.g. positive density and pressure). The method is designed to preserve physical realizability during both reconstruction and time evolution. The idea is to start with an unlimited highorder discontinuous Galerkin method and fall back to a novel adaptiveorder finitedifference scheme if the discontinuous Galerkin solution is not physically realizable. We will present a preliminary test result of our new robust adaptiveorder method in the context of (general) relativistic astrophysics. [Preview Abstract] 
Sunday, April 19, 2020 4:54PM  5:06PM Not Participating 
L09.00008: Kinetic Plasma Simulations of BlackHole Jet Launching and Pair Discharges Kyle Parfrey Black holes drive powerful relativistic jets, using magnetic fields dragged in by their accretion flows. The jets' plasma should be so diffuse as to be effectively collisionless, and selfconsistently supplied by pair creation near the horizon. I will present the first generalrelativistic kinetic plasma simulations of the collisionless magnetospheres of rotating black holes, showing the launching of electromagnetic jets by the BlandfordZnajek mechanism. Simulations with MonteCarlo inverseCompton scattering and twophoton pair creation show that the plasmasupplying discharge is tied to the inner light surface, near the horizon, and that no simple MHD stagnation surface forms. The kinetic approach will be useful for studying the accretion flows of the Event Horizon Telescope targets, Sgr A* and M87, where the plasma is likewise of low density and collisionless, and for probing black holesâ€™ nonthermal Xray and gammaray emission from first principles. [Preview Abstract] 
Sunday, April 19, 2020 5:06PM  5:18PM Not Participating 
L09.00009: Common Envelope Wind Tunnel: The Effects of Binary Mass Ratio and Implications for the AccretionDriven Growth of LIGO Binary Black Holes Soumi De, Morgan Macleod, Rosa Everson, Andrea Antoni, Ilya Mandel, Enrico RamirezRuiz With the impressive number of binary black hole and binary neutron stars mergers observed by the LIGOVirgo detector network in the recent years, it is now important to understand the formation channels of these systems. This talk focuses on the common envelope phase, crucial to the formation of compact object binaries. During this phase, the two companions evolve inside a shared envelope, with the secondary object orbiting towards the core of the primary star. The secondary object interacts with the envelope's fluid material flowing past it, giving rise to drag forces that pull the two stellar cores into a tighter orbit. Additionally, the embedded object can be modified by accretion from the flow around it. We present results from threedimensional hydrodynamical simulations modeling the common envelope inspiral phase using the the "wind tunnel" formalism, and highlight the effects of the full set of flow parameters on accretion and drag forces in these episodes. We point to the key role of the coupled effect of accretion and drag coefficients in modulating the transformation of binaries in common envelope phases, and discuss our understanding of the effect of this phase on the properties of stellarmass black hole populations. [Preview Abstract] 
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