Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session Q12: Numerical Relativity: Black Holes, Neutron Stars and Accretion Disks |
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Sponsoring Units: GGR Chair: Pablo Laguna, Georgia Institute of Technology Room: Royal CD |
Monday, May 2, 2011 10:45AM - 10:57AM |
Q12.00001: Gravitational and Electromagnetic Signatures from the Tidal Disruption of a White Dwarf by an Intermediate Mass Black Hole Roland Haas, Tanja Bode, Roman Shcherbakov, Pablo Laguna Observations of the gravitational and electromagnetic radiation from the tidal disruption of a white dwarf by an intermediate mass black hole (IMBH) could provide evidence for the existence of IMBHs. During the inspiral and violent disruption of the star, the system will emit both gravitational waves and possibly X-ray radiation from the remnant accretion disk around the IMBH, which together will allow both the system's location and internal parameters to be measured. We present results for fully general relativistic hydrodynamics simulations of these encounters focusing on the electromagnetic signatures during the disruption and subsequent accretion. We also present preliminary results for the disruption of a single main sequence star by a black hole binary. [Preview Abstract] |
Monday, May 2, 2011 10:57AM - 11:09AM |
Q12.00002: Simulations of Eccentric Black Hole-Neutron Star Mergers in Full GR Branson Stephens, William East, Frans Pretorius Within the next few years, gravitational waves from merging black holes (BHs) and neutron stars (NSs) may be directly detected, making a thorough theoretical understanding of such systems a high priority. BH-NS mergers may also produce short duration gamma-ray bursts (SGRBs), whose origin represents an important unsolved problem in astrophysics. SGRB afterglow observations along with theoretical studies of globular cluster evolution suggest that some of these events arise from dynamically formed BH-NS binaries, which are likely to merge with non-negligible eccentricity. Motivated by these considerations, we perform simulations of BH-NS binaries with varying eccentricity to explore possible channels of disk formation and evolution following BH-NS mergers, and to look for signatures of the matter dynamics in the gravitational waveforms. [Preview Abstract] |
Monday, May 2, 2011 11:09AM - 11:21AM |
Q12.00003: Ultra Relativistic Fluid Collisions William East, Frans Pretorius, Branson Stephens We describe numerical simulations of the head-on collision of stars in the ultra relativistic regime. This work explores the idea that sufficiently boosted particles generically form black holes, as well as the competition between gravitational and hydro-dynamics. We investigate the degree to which the hoop conjecture describes the dynamics of black hole formation and the role of matter near the threshold for black hole formation. [Preview Abstract] |
Monday, May 2, 2011 11:21AM - 11:33AM |
Q12.00004: Relative stability of black hole threshold solutions in critical gravitational collapse Theodor Brasoveanu, Frans Pretorius We present numerical studies of the relative stability of Type I critical solutions in problems of gravitational collapse. These strong-field, non-trivially dynamic solutions to Einstein equations, initially discovered by M. Choptuik, arise at the threshold of black hole formation. We study the interaction between two different matter models in spherical symmetry (a boson star and a perturbing SU(2) Yang-Mills field) that exhibit the same type of threshold solution. Given the unstable nature of the critical solutions, the central question that we address is how does matter of one type behave in the presence of a critical solution of another type of matter. This question was investigated by Choptuik in the case of Type II collapsing systems, where the scalar field was found to dominate the dynamics of the combined system. Hereby we present results for Type I collapse, using adaptive grid techniques to solve Einstein equations coupled to matter. [Preview Abstract] |
Monday, May 2, 2011 11:33AM - 11:45AM |
Q12.00005: Equilibrium models of general relativistic magnetars Eric Hirschmann We consider equilibrium configurations of strongly magnetized neutron stars in general relativity. Working in axisymmetry but without circularity, we construct rigidly rotating magnetars with both poloidal and toroidal fields in the interior. Using a self-consistent field approach, we investigate the relative contributions from both poloidal and toroidal components. We sketch how our procedure can be extended to incorporate differential rotation and convective motions. [Preview Abstract] |
Monday, May 2, 2011 11:45AM - 11:57AM |
Q12.00006: Gravitational Collapse of k-essence David Garfinkle Numerical simulations are performed of the gravitational collapse of a k-essence scalar field. Under some circumstances black holes form, but under others the system becomes ill posed and the simulation terminates. The k-essence field allows superluminal motion so information can escape from the black hole. [Preview Abstract] |
Monday, May 2, 2011 11:57AM - 12:09PM |
Q12.00007: Super-Extremal Spinning Black Holes via Accretion Pablo Laguna, Tanja Bode, Richard Matzner A Kerr black hole with mass $M$ and angular momentum $J$ satisfies the extremality inequality $J \le M^2$. In the presence of matter and/or gravitational radiation, the bound needs to be reformulated in terms of local measurements of $M$ and $J$ directly associated with the black hole. The isolated and dynamical horizons framework provides such natural quasi-local characterization of $M$ and $J$, making possible in axi-symmetry to reformulate the extremality limit as $J \le 2\,M^2$, with $M$ the irreducible mass computed from the apparent horizon area and $J$ obtained using approximate rotational Killing vectors on the apparent horizon. This condition is also equivalent to requiring a non-negative black hole surface gravity. We present numerical experiments of an accreting black hole that temporarily violates this extremality inequality. [Preview Abstract] |
Monday, May 2, 2011 12:09PM - 12:21PM |
Q12.00008: Non-axisymmetric Instabilites in Thick Magnetised Tori Around Black Holes Tyler Landis, Peter Diener, Erik Schnetter, Burkhard Zink Accretion onto black holes is one of the most likely candidates for generating many high energy events observed in our universe, which include gamma ray bursts, active galactic nuclei, and X-ray binaries. With current computing power, we are now beginning to be able to model some of these potential sources in global three dimensional general relativistic magneto-hydrodynamic (GRMHD) simulations. This gives us the ability to study the nonlinear asymmetric dynamics of these systems. Here, I will present recent results studying the growth of non-axisymetric instabilities in several thick accretion tori models initially in equilibrium around a black hole on a fixed spacetime background focusing on the effects of the presence of a toroidal magnetic field. [Preview Abstract] |
Monday, May 2, 2011 12:21PM - 12:33PM |
Q12.00009: Exploring Stability of General Relativistic Accretion Disks Oleg Korobkin, Ernazar Abdikamalov, Erik Schnetter, Nikolaos Stergioulas, Burkhard Zink Self-gravitating relativistic disks around black holes can form as transient structures in a number of astrophysical scenarios, involving core collapse of massive stars and mergers of compact ob jects. I will present results on our recent study of the stability of such disks against runaway and non-axisymmetric instabilities, which we explore using three-dimensional hydrodynamics simulations in full general relativity. All of our models develop unstable non-axisymmetric modes on a dynamical timescale. We observe two distinct types of instabilities: the Papaloizou-Pringle and the so-called intermediate type instabilities. The development of the non-axisymmetric mode with azimuthal number $m=1$ is accompanied by an outspiraling motion of the black hole, which significantly amplifies the growth rate of the $m=1$ mode in some cases. We will discuss the types, growth rates and pattern speeds of the unstable modes, as well as the detectability of the gravitational waves from such objects. [Preview Abstract] |
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