Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session Y14: Astrophysical Numerical Relativity Simulations |
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Sponsoring Units: GGR Chair: Pablo Laguna, Georgia Institute of Technology Room: Plaza Court 3 |
Tuesday, April 16, 2013 1:30PM - 1:42PM |
Y14.00001: Three-Dimensional General Relativistic Simulations of Core-Collapse Supernovae Ernazar Abdikamalov, Christian D. Ott, Philipp Moesta, Roland Haas, Steve Drasco, Evan O'Connor, Christian Reisswig, Casey Meakin, Erik Schnetter Despite decades of effort, the explosion mechanism of core-collapse supernovae is still not well understood. Spherically-symmetric models fail to explode, suggesting that multi-dimensional effects are of crucial importance. Studies in axisymmetry (2D) reveal that the standing accretion shock instability (SASI) and neutrino-driven convection are pivotal ingredients for successful explosions. Axisymmetry, however, is a rather poor approximation of this scenario. 3D studies, on the other hand, are still in their infancy and employ crude approximations. As a result, the exact role of the SASI and convection is still not well established. In this talk, I will present our study of the 3D hydrodynamics of the post-bounce phase of the collapse of a 27 solar-mass star. We perform 3D general-relativistic simulations with a neutrino leakage/heating scheme. In our simulations, neutrino-driven convection becomes the dominant instability and leads to large-scale non-oscillatory deformations of the shock front, resulting in strongly aspherical explosions. Low-l-mode SASI oscillations are present in our models, but saturate at small amplitudes. [Preview Abstract] |
Tuesday, April 16, 2013 1:42PM - 1:54PM |
Y14.00002: General Relativistic Simulations of Magnetized Plasmas around Black Holes Fatemeh Hossein-Nouri Black hole accretion flows and jets are qualitatively affected by the presence of the magnetic fields. We study fully three dimensional simulations of a magnetized thick accretion disk around a spinning black hole perturbed initially by weak poloidal magnetic fields using and developing the general relativistic magnetohydrodynamics (GRMHD) code SpEC. Our goal is to enhance SpEC in order to simulate magnetized binary mergers in the future. We set a number of tests to develop our GRMHD code and we report the current status of testing it in the simulation of a magnetized accretion torus around a black hole. We explore how magnetic fields affect the dynamics of the plasma and the possibility of observing relativistic jets and resolving the magnetorotational instabilities. [Preview Abstract] |
Tuesday, April 16, 2013 1:54PM - 2:06PM |
Y14.00003: Accretion disks around kicked black holes: Post-kick Dynamics Marcelo Ponce, Joshua A. Faber, James C. Lombardi Numerical calculations of merging black hole binaries indicate that asymmetric emission of gravitational radiation can kick the merged black hole at up to thousands of km/s, a number of systems have been observed whose properties are consistent with an active galactic nucleus containing a supermassive black hole moving with substantial velocity with respect to its broader accretion disk. We study the effect of an impulsive kick delivered to a black hole on the dynamical evolution of its accretion disk using a Smoothed Particle Hydrodynamics code, focusing attention on the role played by the kick angle with respect to the orbital angular momentum vector of the pre-kicked disk. We find that for more vertical kicks, for which the angle between the kick and the normal vector to the disk $\theta \le 30^\circ$, a gap remains present in the inner disk, in accordance with the prediction from an analytic collisionless Keplerian disk model, while for more oblique kicks with $\theta \ge 45^\circ$, matter rapidly accretes toward the black hole. There is a systematic trend for higher potential luminosities for more oblique kick angles for a given black hole mass, disk mass and kick velocity, and we find large amplitude oscillations in time for a $60^\circ$ kick from the vertical. [Preview Abstract] |
Tuesday, April 16, 2013 2:06PM - 2:18PM |
Y14.00004: Force Free Magnetospheres of Kerr Black holes Govind Menon Preliminary analysis for an exact solution describing the extraction of energy from supermassive astrophysical black holes will be presented. These solutions should also provide a benchmark test solution for the various numerical codes that simulate the active magnetospheres of Kerr Black holes. [Preview Abstract] |
Tuesday, April 16, 2013 2:18PM - 2:30PM |
Y14.00005: Tidal Disruption of a Star By a Massive Black Hole: the Fate of the Debris Roseanne Cheng, Charles Evans, Tamara Bogdanovic When a star disrupts near a black hole, some of the debris is ejected from the system and the rest that is bound eventually accretes onto the black hole. The fate of the debris is dependent on the type of star and the mass and spin of the black hole. We present results of a numerical code constructed to obtain accurate simulations of relativistic encounters between a star and a massive black hole. The tidal interaction is calculated in Fermi normal coordinates (FNC), a frame centered on the star. We simulate an encounter between a white dwarf and an intermediate mass black hole at the threshold of disruption. While Newtonian treatment of hydrodynamics and self-gravity is sufficient to accurately describe the structure of the star, we find that there are several significant relativistic terms in the expansion [of the black hole's tidal field] that should be retained. We consider the importance of these terms for the dynamics of the debris from the tidally disrupted star. [Preview Abstract] |
Tuesday, April 16, 2013 2:30PM - 2:42PM |
Y14.00006: Magnetic effects on the low-T/W instability in proto-neutron stars Curran Muhlberger Dynamical instabilities in proto-neutron stars may produce gravitational waves whose observation could shed light on the physics of core-collapse supernovae. When born with sufficient differential rotation, these stars are susceptible to a low-T/W instability, but such rotation can also amplify magnetic fields to strengths where they have a considerable impact on the dynamics of the stellar matter. These fields might suppress the low-T/W instability or enable additional non-axisymmetric behavior, complicating future observational interpretations. Using a new MHD module for the Spectral Einstein Code, we have simulated these systems in full 3D GRMHD. Here we will discuss the results of these studies, examining the interplay between fluid and magnetic instabilities in the early lives of neutron stars. [Preview Abstract] |
Tuesday, April 16, 2013 2:42PM - 2:54PM |
Y14.00007: Neutron-star mergers in scalar-tensor theories of gravity Enrico Barausse, Carlos Palenzuela, Marcelo Ponce, Luis Lehner Scalar-tensor theories of gravity are natural phenomenological alternatives to General Relativity. In these theories, the gravitational interaction is mediated by a scalar degree of freedom, besides the gravitons. In regions of the parameter space of these theories where constraints from both solar system experiments and binary-pulsar observations are satisfied, we show that binaries of neutron stars present marked differences from General Relativity in both the late-inspiral and merger phases. These strong-field effects are difficult to reproduce in General Relativity, even with an exotic equation of state. Further, we discuss possible detectability of these differences with Advanced LIGO/VIRGO as well as astrophysical implications in possible models for energetic electromagnetic events. [Preview Abstract] |
Tuesday, April 16, 2013 2:54PM - 3:06PM |
Y14.00008: Spontaneous Scalarization with Dynamical General Relativity Fethi M Ramazanoglu, Frans Pretorius Even though scalar-tensor theories are among the best-known alternatives to general relativity, solar system and binary pulsar observations rule out a large portion of their parameter spaces. Spontaneous scalarization is a non-perturbative case of scalar-tensor theories for which large deviations from general relativity can be observed in the regions of high energy density in compact stars, while the known observational bounds can be satisfied far away from the compact objects. We study this scenario with full numerical relativity for various cases of compact object mergers, and deduce the optimal ways of testing general relativity and/or further restricting the parameter space of alternative theories from observational data. [Preview Abstract] |
Tuesday, April 16, 2013 3:06PM - 3:18PM |
Y14.00009: Stiffness effects on the dynamics of bar-mode instability in full General Relativity Frank L\"offler, Roberto De Pietri, Alessandra Feo, Luca Franci We present results on the effect of the stiffness of the equation of state on dynamical bar-mode instability in rapidly rotating polytropic models of neutron stars in full General Relativity. We determine the change on the threshold for the emergence of the instability when the adiabatic $\Gamma$ index is changed from 2 to 2.75 to mimic the behavior of realistic equation of state. We also extend the analysis to low value of the instability parameter $\beta$ to check for the presence of low-$\beta$ or shearing instabilities. [Preview Abstract] |
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