Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session G15: Numerical Modeling of Binaries with MatterLive
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Sponsoring Units: DGRAV Chair: Zachariah Etienne, West Virginia University |
Sunday, April 18, 2021 8:30AM - 8:42AM Live |
G15.00001: Electromagnetic Emission from a Binary Black Hole Merger Remnant in Plasma: Field Alignment and Plasma Temperature Bernard Kelly, Zachariah Etienne, Jacob Golomb, Jeremy Schnittman, John Baker, Scott Noble, Geoffrey Ryan Comparable-mass black-hole mergers generically result in moderate to highly spinning holes, whose spacetime curvature will significantly affect nearby matter in observable ways. We investigate how the moderate spin of a post-merger Kerr black hole immersed in a plasma with initially uniform density and uniform magnetic field affects potentially observable accretion rates and energy fluxes. Varying the initial specific internal energy of the plasma over two decades, we find very little change in steady-state mass accretion rate or Poynting luminosity, except at the lowest internal energies, where fluxes do not exhibit steady-state behavior during the simulation timescale. Fixing the internal energy and varying the initial fixed magnetic-field amplitude and orientation, we find that the steady-state Poynting luminosity depends strongly on the initial field angle with respect to the black hole spin axis, while the matter accretion rate is more stable until the field angle exceeds $sim 45\degree$. The proto-jet formed along the black hole spin-axis conforms to a thin, elongated cylinder near the hole, while aligning with the asymptotic magnetic field at large distances. [Preview Abstract] |
Sunday, April 18, 2021 8:42AM - 8:54AM Live |
G15.00002: Analyzing properties from black hole-neutron star merger outflows and modeling r-process nucleosynthesis Teresita Ramirez, Francois Foucart The LIGO and Virgo observatories have made over 35 gravitational wave detections thus far. Most of the signals detected have been confidently identified as either black-hole binaries, neutron-star binaries, or black hole-neutron star binaries. Near the time of merger, the only known way to solve Einstein’s equations to model these strongly gravitating systems is to use numerical relativity because then all pencil-and-paper approximations fail. Using the SXS Collaborations’ numerical relativity code, the Spectral Einstein Code (SpEC), I completed a hydrodynamic black hole-neutron star merger simulation to test and model the creation of heavy elements in a process called r-process nucleosynthesis to estimate the outflows of the merger. Investigating the ejected matter from BHNS mergers has been done before; however, for this project, we explored how r-process heating affects our estimations of how much matter is ejected from the merger. [Preview Abstract] |
Sunday, April 18, 2021 8:54AM - 9:06AM Live |
G15.00003: Numerical Inside View of Hypermassive Remnant Models for GW170817 Wolfgang Kastaun, Frank Ohme The first multi-messenger observation of a binary neutron star merger has already lead to first constraints on the nuclear matter equation of state. To make the most out of the observational data, however, the theoretical modeling of the merger process needs to be improved further. Among other ingredients, the evolution of the merger remnant within tens of milliseconds after the merger is essential, since it is connected to the kilonova as well as to the short gamma ray burst. Key aspects linking this early phase to the observables of later stages are the fate of the remnant, the mass of the disk, dynamical matter ejection, and disk winds. These in turn are influenced by the interplay with the remnant and hence the delay before black hole formation. Modeling the remnant lifetime and collapse is a difficult challenge for current methods. In this talk, I will present results of numerical simulations that highlight the complexity of the most basic hydrodynamic evolution without magnetic fields, and show novel visualizations of the three-dimensional remnant structure. [Preview Abstract] |
Sunday, April 18, 2021 9:06AM - 9:18AM Live |
G15.00004: The Role of Strong Gravity and the Nuclear Equation of State on Neutron-Star Common-Envelope Accretion A. Miguel Holgado, Hector Silva, Paul Ricker, Nicolas Yunes Common-envelope evolution is important in the formation of neutron star binaries within the isolated binary formation channel. In this channel, gravitational drag drives orbital inspiral, either leading to envelope ejection if enough energy is dissipated, or a merger with the primary's core, otherwise. Because neutron stars are in the strong-gravity regime, they have a substantial relativistic mass deficit, i.e., their gravitational mass is less than their baryonic mass. This effect causes some fraction of the accreted baryonic mass to convert into neutron star binding energy. The relativistic mass deficit also depends on the nuclear equation of state, since more compact neutron stars will have larger binding energies. We model the mass growth and spin-up of neutron stars inspiraling within common-envelope environments and quantify how different initial binary conditions and hadronic equations of state affect the post-common-envelope neutron star's mass and spin. From these models, we find that neutron star mass growth is suppressed by $\approx 15-30\%$. This work demonstrates that a neutron star’s strong gravity and nuclear microphysics plays a role in neutron-star-common-envelope evolution, in addition to the macroscopic astrophysics of the envelope. [Preview Abstract] |
Sunday, April 18, 2021 9:18AM - 9:30AM Live |
G15.00005: Sub-Grid Viscosity in Neutron Star Simulations with SpEC Alexander Knight Viscosity in neutron star simulations is capable of approximately replicating the angular momentum transportation and heating produced by instabilities that are currently too costly to capture in simulations, yet affect the gravitational wave, matter outflows, neutrino emission, and remnant of neutron star binaries. In this talk, we will present an energy conserving addition to the large eddy viscosity formalism for subgrid modeling, as well as cost and behavior comparisons between the large eddy formalism and the Israel-Stewart formalism for a differentially rotating neutron star. [Preview Abstract] |
Sunday, April 18, 2021 9:30AM - 9:42AM Live |
G15.00006: Revealing a strong phase transition in neutron star mergers with gravitational waves Sebastian Blacker, Niels-Uwe Bastian, Andreas Bauswein, David Blaschke, Tobias Fischer, Micaela Oertel, Theodoros Soultanis, Stefan Typel Binary neutron star mergers allow us to study matter at extreme densities. Under these conditions the state of matter is currently not fully understood. As the density increases during merging, a transition from hadronic to deconfined quark matter may take place. We present a procedure to identify a strong phase transition occurring during a neutron star merger by simultaneously analyzing gravitational waves emitted before and after the coalescence of the two stars. Furthermore, our method can estimate the densities reached during the merger. This immediately places upper limits on the transition density of the hadron-quark phase transition if signs of such a transition are found. If no evidence of a transition is present, lower limits on the transition density can be inferred. Hence, a single, sufficiently accurate simultaneous detection of pre- and postmerger gravitational waves will help to constrain the onset density of the quark-hadron phase transition. [Preview Abstract] |
Sunday, April 18, 2021 9:42AM - 9:54AM Live |
G15.00007: The Polarized Image of Fluid Orbiting a Kerr Black Hole Zachary Gelles, Elizabeth Himwich, Daniel Palumbo, Michael Johnson, Ramesh Narayan We present a semi-analytic model to compute the polarized image of equatorial synchrotron emission near a Kerr black hole. For face-on viewing inclinations, we show that the geometrical effect of spin on the observed polarization is subleading, suggesting that astrophysical properties of the accretion flow and plasma are primarily responsible for differences seen in ray-traced images of general relativistic magnetrohydrodynamic simulations. We also present numerical results for large inclination angles, at which the effects of spin become more apparent. As an additional application of our model, we analyze the polarized appearance of “hotspots” orbiting on equatorial geodesics. We demonstrate that the linear polarization exhibits distinct signatures for different field configurations and inclination angles, and we compare our results to previous modelling efforts and to radio and near-infrared observations of the Galactic Center supermassive black hole, Sgr A*. [Preview Abstract] |
Sunday, April 18, 2021 9:54AM - 10:06AM Live |
G15.00008: Efficient Fully-Numerical Einstein-GRMHD Simulations in Curvilinear Coordinates Yosef Zlochower, Vassilios Mewes, Manuela Campanelli, Thomas Baumgarte, Zachariah Etienne, Federico Lopez Armengol, Federico Cipolletta Here we describe techniques that we developed to efficiently evolved the Einstein Equations coupled to the equations for Magnetohydrodynamics in curvilinear coordinates. In particular, we focus on spherical coordinates and the challenges of producing accurate and efficient simulations in the presence of the coordinate singularities on the polar axis and the origin. As test cases, we present evolutions of stable and unstable magnetized rotating neutron stars, including collapse scenarios, as well as accurate simulations of gravitational waveforms. [Preview Abstract] |
Sunday, April 18, 2021 10:06AM - 10:18AM Live |
G15.00009: Motion of a hyperelastic sphere in Schwarzschild spacetime Nishita Jadoo, J. David Brown We simulate the motion of a 10 cm hyperelastic sphere in Schwarzschild spacetime. We use a finite element discretization of the sphere and a Lagrangian formulation of the equations of motion to evolve each node. After obtaining the worldline of each node, we choose a fiducial node and set up a Fermi normal frame (FNF) at that node. Since the size of the sphere is small compared to the curvature of spacetime, we approximate the metric in the FNF as nearly flat. We look at both a close encounter orbit as well as a radial plunge. We plot the spatial coordinates of the nodes in the FNF and observe the sphere as it deforms, oscillates and rotates. The observed oscillation frequency in the FNF agree with the lowest-frequency ellipsoidal mode for small oscillations of a free solid elastic sphere. We integrate the stress-energy-momentum tensor to obtain the spin, internal energy and center of mass in the FNF. We observe the changes in spin and internal energy as the sphere interacts with the black hole. [Preview Abstract] |
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