Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session J13: Numerical Relativity: Neutron Stars and Other Sources with Matter |
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Sponsoring Units: DGRAV DCOMP Chair: John Baker, NASA Room: A224-225 |
Sunday, April 15, 2018 1:30PM - 1:42PM |
J13.00001: Assessing confidence in numerical relativity waveforms of binary neutron star mergers Roland Haas, Shawn Rosofsky, Sebastiano Bernuzzi, Tim Dietrich, Bruno Giacomazzo, Riccardo Ciolfi, Daniel Johnson, Eliu Huerta The first multi-messenger detection in gravitational waves and the electromagnetic spectrum of a binary neutron star merger GW170817 underlined the need for numerical relativity simulations of the neutron star merger to reliably predict waveforms and to inform astrophysical models of the event that predict the long term electromagnetic signals observed from such an event. Here we present a progress report on work aimed at comparing waveform predictions obtained by different numerical relativity codes to assess whether the codes agree within their stated error bars. To this end we simulate in typical binary neutron star merger using two neutron star equations of state (SLy and MS1b) that bracket the range of realistic equations of state expected in neutron stars. Using multiple independent codes, and involving scientists at different institutions, we independently compute error bars for each code and verify whether the predicted gravitational waveform signal agrees between the different simulations for simulations using realistic computational resources. Only after a reliable error bound on the numerical relativity simulations has been established can their waveform templates be used to construct semi-analytic waveform templates for LIGO data analysis. [Preview Abstract] |
Sunday, April 15, 2018 1:42PM - 1:54PM |
J13.00002: Effects of a new Equation of State on Binary Neutron Star Mergers Andrea Endrizzi, Domenico Logoteta, Bruno Giacomazzo, Ignazio Bombaci, Riccardo Ciolfi, Wolfgang Kastaun We present results of fully general relativistic simulations of binary neutron star mergers employing a new cold chiral effective field theory equation of state that we named $BL$. We offer a comparison with respect to a standard relativistic mean field equation of state ($GM3$) and give a full analysis of the dynamics during both the inspiral and post-merger phases. We extract the gravitational wave signal for all our simulations and analyze differences in the signals from different models. We also describe the effects of this new equation of state on the dynamics of the ejecta and on possible electromagnetic counterparts. [Preview Abstract] |
Sunday, April 15, 2018 1:54PM - 2:06PM |
J13.00003: GW170817, General Relativistic Magnetohydrodynamic Simulations, and the Neutron Star Maximum Mass Milton Ruiz, Stuart Shapiro, Antonios Tsokaros Coincident detections of gravitational waves with electromagnetic signals can be used to constrain the nature of the progenitor of GW170817/GRB170817A. Combining the observational data with our recent fully general relativistic magnetohydrodynamic numerical simulations we conclude that the progenitor represents the merger of a magnetized binary neutron star that undergoes delayed collapse to a black hole immersed in a magnetized disk of tidal debris. This conclusion leads to a bound on the maximum mass of a cold, spherical neutron star (the TOV limit): ${M_{\rm max}^{\rm sph}}\leq2.74/\beta$, where $\beta$ is the ratio of the maximum mass of a uniformly rotating neutron star (the supramassive limit) over the maximum mass of a nonrotating star. Causality arguments allow $\beta$ to be as high as $1.27$, while most realistic candidate equations of state predict $\beta$ to be closer to $1.2$, yielding ${M_{\rm max}^{\rm sph}}$ in the range $2.16-2.28 M_\odot$. Assumptions and caveats, which can be removed by further numerical simulations and analysis, are also discussed. [Preview Abstract] |
Sunday, April 15, 2018 2:06PM - 2:18PM |
J13.00004: Spin in binary neutron star initial data Antonios Tsokaros, Koji Uryu, Milton Ruiz, Stuart Shapiro The rotation of a single star can be described by different quantities such as the angular momentum, the angular velocity, the dimensionless spin parameter, the quasi-local spin, as well as the circulation. For single, slowly rotating stars curves of mass versus density at constant quasi-local spin almost coincide (up to a constant) with curves at constant circulation. For highly spinning stars this is no longer true. Since for isentropic fluids dynamical evolution conserves the baryon mass, entropy, and circulation, we propose the use of circulation in order to parametrize the spin in binary neutron stars. We present the first constant circulation sequences of a binary system at different separations using a piecewise polytropic equation of state. We show that, at least for slowly rotating stars, the quasi-local spin is also approximately conserved along the sequence similarly to single rotating stars. We also present a new decomposition for the fluid velocity in the spinning formulation that simplifies the equations and makes the identification of the spin with the circulation of single stars closer. [Preview Abstract] |
Sunday, April 15, 2018 2:18PM - 2:30PM |
J13.00005: Quasi-radial instability of differentially rotating relativistic stars Gabriele Bozzola, Nikolaos Stergioulas, Roberto De Pietri The stability against gravitational collapse of the remnant left by a merger of binary neutron stars is of great interest in gravitational-wave astronomy. This property can be explored with simulations in full general relativity, which are often computational extremely demanding. A well-established result in this landscape is that the rotation of the remnant is a crucial factor in determining its stability. In the case of uniform rotation, the turning-point method provides a shortcut to study physical properties regarding the stability of neutron stars in a more affordable way. This method is based on the study of the turning points, particular equilibrium models that satisfy a specific condition a that can be found without performing full simulations. Here, we applied the turning-point method to differentially rotating neutron stars, obtaining an estimation of the location of the instability region in the parameter space, for different equations of state and rotation laws. To validate this approach we performed three-dimensional simulations of select models to find the onset of dynamical instability. Finally, we report on universal relations among some of the physical properties of interest along the sequence of turning-point models. [Preview Abstract] |
Sunday, April 15, 2018 2:30PM - 2:42PM |
J13.00006: Study of f-mode Oscillations in Numerical Relativity Simulations of Perturbed Neutron Stars and Highly Eccentric Binary Neutron Star Mergers Shawn Rosofsky, Roman Gold, Cecilia Chirenti, Cole Miller We discuss results from high-resolution numerical relativity (NR) simulations of neutron star (NS) f-mode oscillations obtained with the Einstein Toolkit. We excited isolated NSs in one of their eigenmodes, evolved the system via NR simulations and compared different reconstruction methods, spacetime evolution formalisms, perturbation amplitudes and grid spacings. We identify settings that resolve the physical damping time of the f-mode oscillations due to gravitational wave (GW) losses on a secular time scale via convergence analysis and comparison to linear results. Informed by the former idealized models, we performed NR simulations of highly eccentric binary NS mergers studying GWs from tidally excited f-mode oscillations that may be observable with third generation GW detectors. We compared the f-modes in the binary case to the perturbed isolated NS cases. These initial studies form the basis for more realistic models with different equations of state and compactness, which we will study in the near future to investigate our capability to constrain the equation of state of matter at supranuclear densities. [Preview Abstract] |
Sunday, April 15, 2018 2:42PM - 2:54PM |
J13.00007: Black hole-neutron star post-merger evolution using viscous relativistic hydrodynamics Milad Haddadi The post-merger evolution of black hole-neutron star and neutron star-neutron star systems is driven by magnetohydrodynamic turbulence. Such multiscale problems are very costly to simulate. One approach is to use artificially large seed magnetic fields to resolve the magnetorotational instability. Another is to add some model of subgrid-scale effects, with subgrid angular momentum transport often being modeled as a shear viscosity. We simulate the disk from a black hole-neutron star model in both ways and compare results. We present a new implementation of the relativistic Navier-Stokes equations in the Spectral Einstein Code, with accompanying star and accretion torus tests. For the post-merger system, we analyze the combination of shocks and turbulent/viscous dissipation acting to heat the disk in the early post-merger phase. [Preview Abstract] |
Sunday, April 15, 2018 2:54PM - 3:06PM |
J13.00008: Evolution of the Magnetized, Neutrino-Cooled Accretion Disk in the Aftermath of a Black Hole Neutron Star Binary Merger Fatemeh Hossein Nouri, Matthew Duez, Francois Foucart, M. Brett Deaton, Roland Haas, Milad Haddadi, Lawrence Kidder, Christian Ott, Harald Pfeiffer, Mark Scheel, Bela Szilagyi Black hole-accretion disk systems from compact binary mergers are possible engines for short duration gamma-ray bursts (GRBs). In this scenario the evolution of the post-merger remnant torus is determined by a combination of neutrino cooling and magnetically-driven heating processes. We study the post-merger evolution of a magnetized black hole-neutron star binary system using results from a previous numerical relativity simulation and Einstein's Spectral Code's MHD module. We use finite-temperature tabulated equation of state, and leakage scheme to study the neutrino effects. In order to check the reliability of our results, we evolve the system with two different numerical methods: 1) using the cubed-sphere multipatch grids with an improved method for thermal evolution, dealing with supersonic accretion flows more accurately, and 2) using the cartesian grid with SpEC's conservative MHD formalism. We find that a seed magnetic field triggers a sustained source of heating, but its thermal effects are largely cancelled by the advection cooling and expansion of the torus from the MHD-related effects. [Preview Abstract] |
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