Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session L11: Numerical Relativity: Neutron Stars and Other Sources with Matter |
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Sponsoring Units: DGRAV Chair: David Radice, Princeton University Room: Sheraton Governor's Square 17 |
Sunday, April 14, 2019 3:30PM - 3:42PM |
L11.00001: Interactions of Primordial Black Hole with Neutron Star Hyun Lim, William East Several recent studies show that constraints can be put on primordial black holes (PBHs) as a candidate for dark matter by considering their capture by neutron stars (NSs). If a PBH is captured by a NS, the NS is accreted onto the PBH and eventually collapses. A related scenario arises from asymmetric dark matter particles collecting in the center of NS, and eventually forming a small BH. In this work, we study such systems where a small BH has formed in the center of a NS, and follow the dynamics as the small BH consumes the NS from inside. We solve numerically the coupled system of equations formed by the Einstein equations and hydrodynamics under spherical symmetry. Using numerical simulations, we examine the time scale for the NS to collapse into the PBH, and the possible unbounded material from the NS. |
Sunday, April 14, 2019 3:42PM - 3:54PM |
L11.00002: Binary neutron stars with high compactness and spin Wolfgang H Tichy, Alireza Rashti, Tim Dietrich, Reetika Dudi Over the past few years we have developed a formalism to construct binary neutron star initial data with in principle arbitrary masses, spins and eccentricities. However, in practical implementations it has been hard to achieve highly compact, or highly spinning stars. Here we discuss several improvements that allow us to construct initial data also in these cases, so that we now can cover the entire parameter space. When we construct such initial data one has to specify parameters such as a rotation parameter for each star. In order to compare with other calculations or measurements one would like to relate these parameters to more physical quantities such as spin. To facilitate this, we introduce simple estimates for the spin, momentum, mass and center of mass of each individual star. We also show some results from evolutions of highly compact stars. |
Sunday, April 14, 2019 3:54PM - 4:06PM |
L11.00003: Binary neutron star evolutions with high spin Alireza Rashti, Bernd Bruegmann, Tim Dietrich, Reetika Dudi, Wolfgang H Tichy We have developed a method that allows us to construct initial data for |
Sunday, April 14, 2019 4:06PM - 4:18PM |
L11.00004: Black Hole-Neutron Star mergers in the parameter range of GW170817 Francois V Foucart We present simulations of low-mass black hole-neutron star (BHNS) mergers performed with the SpEC code. Black holes of less than two solar masses have never been observed, but cannot at this point be ruled out. The observation of a gravitational wave (GW) signal from a BHNS binary with such a low mass black hole would nearly certainly be mistaken for a binary neutron star (BNS) mergers. We use our simulations to study mass ejection and disk formation in low-mass BHNS mergers, and extract information regarding the observable properties of these systems. We also use our results to show that, even though the observed GW170817 event was most likely a BNS merger, a wide range of BHNS binary parameters remain compatible with both the GW signal and the bolometric kilonova light curve. |
Sunday, April 14, 2019 4:18PM - 4:30PM |
L11.00005: Complete initial value spacetimes containing black holes in general relativity:Application to black hole-disk systems Antonios Tsokaros, Koji Uryu, Stuart Louis Shapiro We present a new initial data formulation to solve the full set of Einstein equations for spacetimes that contain a black hole under general conditions. The method can be used to construct complete initial data for spacetimes (the full metric) that contain a black hole. For stationary, axisymmetric spacetimes our method yields Kerr-Schild black holes in vacuum and rotating equilibrium neutron stars. We demonstrate the power of our new method by solving for the first time the whole system of Einstein equations for a nonaxisymmetric, self-gravitating torus in the presence of a black hole. The black hole has dimensionless spin 0.99, a rotation axis tilted at a 30 degrees angle with respect to the angular momentum of the disk, and a mass of approximately 1/5 of the disk. |
Sunday, April 14, 2019 4:30PM - 4:42PM |
L11.00006: Simulating the Magnetorotational Collapse of Supermassive Stars: Incorporating Gas Pressure Perturbations and Different Rotation Profiles Lunan Sun, Milton Ruiz, Stuart Louis Shapiro Collapsing supermassive stars with masses M≳10^{4−6}M⊙ have long been speculated to be the seeds of supermassive black holes. We previously performed GRMHD simulations of marginally stable magnetized Γ=4/3 polytropes uniformly rotating at the mass-shedding limit to model the direct collapse of SMSs and obtained a black hole-disk system which launched an incipient jet. Here we perform GRMHD simulations of Γ≳4/3 polytropes to account for the perturbative role of gas pressure in SMSs. We also consider different initial stellar rotation profiles. The stars are initially seeded with a dynamically weak dipole magnetic field that is either confined to the stellar interior or extended to the stellar exterior. We find that the mass of BH depends sharply on Γ−4/3 and the initial stellar rotation profile. Following the BH formation, a jet is launched and its duration is consistent with long gamma-ray bursts. Our results suggest that the Blandford-Znajek mechanism powers the jet. They are also in agreement with our proposed universal model that estimates accretion rates and luminosities that characterize magnetized BH-disk remnant systems that launch a jet. |
Sunday, April 14, 2019 4:42PM - 4:54PM |
L11.00007: Spritz: a new fully general relativistic magnetohydrodynamic code Federico Cipolletta I will present a new general relativistic magnetohydrodynamic (GRMHD) code devoted to the study of compact binary mergers with finite temperature equations of state and neutrino emission. Numerical modeling of neutron stars binaries, black holes binaries, and neutron star-black hole binaries has now become one of the most important fields of study in theoretical astrophysics because it allows extracting physical information from the gravitational wave and electromagnetic signals by comparing simulated data with observations. Focusing on the NS-NS and NS-BH cases, in particular, it has been shown many times that only a fully general relativistic treatment taking also into account magnetic fields may give a complete picture of this scenario and this requires to solve the equations of GRMHD. In order to let the so-called divergence-free condition be automatically satisfied, I considered the magnetic field coming out from a vector potential. In addition, I also consider a general treatment for the NS Equation Of State (EOS) allowing for the use of finite temperature tabulated EOS. This new code will also implement neutrino cooling in order to provide a more accurate study of the post-merger phase. |
Sunday, April 14, 2019 4:54PM - 5:06PM |
L11.00008: Simulating Accretion Disks With Discontinous Galerkin Methods Nils Deppe Discontinuous Galerkin methods have recently seen a lot of interest as a new |
Sunday, April 14, 2019 5:06PM - 5:18PM |
L11.00009: An Implementation of Axisymmetry in Numerical Relativity Using a Multipatch Scheme Jerred Jesse With the observation of a kilonova signal following the detection of the binary neutron star merger GW170817, the need for an extended duration simulation of the post-merger environment has become important in order to determine the effects of the stability of the remnant by secular processes on any observed signals. In order to extend simulation times in the Spectral Einstein Code (SpEC), we have developed a modification to SpEC's multipatch coordinate transformation implementation to allow for easily running a post-merger simulation in axisymmetry without the need to explicitly rewrite evolved equations in an axisymmetric form. Several tests using simple equilibrium systems with magnetic fields, neutrino transport, and viscosity have shown the viability of this method and demonstrated a significant decrease in required computational resources versus a full 3D simulation. |
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