Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session T11: Neutron Star and Black Hole Binary Simulations |
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Sponsoring Units: GGR Chair: Steven Detweiler, University of Florida Room: Plaza Court 1 |
Monday, May 4, 2009 3:30PM - 3:42PM |
T11.00001: Black Hole - Neutron Star Binary Simulations at Georgia Tech Roland Haas Mixed compact object binaries consisting of a black hole and a neutron star are expected to be not only one of the primary sources of gravitational radiation to be observed by interferometric detectors but also the central engine of short gamma-ray bursts. We report on the status of our effort at Georgia Tech to model these mixed binary systems using the moving puncture method. The results are obtained with an enhanced version our vacuum MayaKranc code coupled to the hydrodynamics Whisky code. We present preliminary results of gravitational waveforms and the disruption of the neutron star for simple polytropic equations of state. [Preview Abstract] |
Monday, May 4, 2009 3:42PM - 3:54PM |
T11.00002: A new numerical method for the construction of binary neutron star initial data Wolfgang Tichy We present a new numerical method for the generation of binary neutron star initial data using the Wilson-Mathews or conformal thin sandwich approach. Our method uses six different computational domains, which include spatial infinity. Each domain has its own coordinates which are chosen such that the star surfaces always coincide with domain boundaries. We use an efficient pseudospectral method to solve the elliptic equations associated with the conformal thin sandwich approach. The main purpose is to introduce our new method and to present code tests for several different configurations. [Preview Abstract] |
Monday, May 4, 2009 3:54PM - 4:06PM |
T11.00003: Simulations of Black Hole-Neutron Star Binaries Francois Foucart, Matthew Duez, Lawrence Kidder, Harald Pfeiffer, Mark Scheel, Saul Teukolsky We present our latest simulations of the inspiral and merger of black hole-neutron star binaries. Our evolutions use the two-grid approach: the Einstein equations are solved in generalized harmonic coordinates using pseudospectral methods, while the relativistic fluid equations are evolved on a separate grid using shock-capturing finite difference techniques. We explore the effects of different mass ratios, black hole spins, and neutron star equations of state on the behavior of the binaries. We extract gravitational waveforms from the simulations and observe for some binary parameters the formation of a long-lived accretion disk. [Preview Abstract] |
Monday, May 4, 2009 4:06PM - 4:18PM |
T11.00004: Neutrino Transport in General Relativistic Neutron Star Evolutions Pedro Marronetti, Stephen Bruenn Binary neutron star and neutron star / black hole mergers will only be accurately modeled when all the key microphysics is included: magnetic fields, photon and neutrino radiation and nuclear networks, all of which should be implemented in a full GR algorithmic infrastructure. Great progress has been made recently with the addition of MHD to current numerical full-GR codes. On the other hand, the addition of neutrino transport to the simulations has yet to be explored. Neutrino radiation is an essential part of state-of-the-art core collapse supernovae simulations, where it has shown to have a preponderant role in the production of the corresponding explosions. While this seems to indicate that neutrino interactions might play an important role in compact object mergers too, this still remains poorly understood. I will report on progress made on the implementation of neutrino transport to our code GRHyd and the different approaches to the task. [Preview Abstract] |
Monday, May 4, 2009 4:18PM - 4:30PM |
T11.00005: Evolutions of Magnetized Neutron Stars Steven Liebling, Matthew Anderson, Eric Hirschmann, Luis Lehner, Patrick Motl, David Neilsen, Carlos Palenzuela, Joel Tohline Magnetized neutron stars, whether considered individually or within compact binary systems, demonstrate a number of interesting dynamical effects and may represent an important source of observable gravitational waves. In addition, isolated, rotating, magnetized stars serve as a good testbed for a necessarily complex, distributed adaptive mesh refinement (AMR) code. As initial data, we use fully consistent, magnetized, rotating stellar configurations generated with the Lorene toolkit. Here results are presented which (i) demonstrate convergence and stability of the code, (ii) show the evolution of stable and unstable magnetized stars, and (iii) study the effects of a scheme to track the leakage of neutrinos. [Preview Abstract] |
Monday, May 4, 2009 4:30PM - 4:42PM |
T11.00006: Magnetic field effects on non-vacuum binaries Matthew Anderson, Eric Hirschmann, Luis Lehner, Steven Liebling, Patrick Motl, David Neilsen, Carlos Palenzuela, Joel Tohline Observational evidence suggests that sizeable magnetic fields are present in a fair number of neutron star binaries and neutron star-black hole binaries. These magnetic fields can have a strong influence on the fluid's dynamics, the energetics of the system and even the production of gravitational radiation. We present results of non-vacuum binary neutron star and black hole- neutron star collisions and examine the influence of magnetic fields on the gravitational waves, fluid structure and dynamical behavior of the system. [Preview Abstract] |
Monday, May 4, 2009 4:42PM - 4:54PM |
T11.00007: General Relativistic Simulations of Black Hole-Neutron Star Mergers: Effects of Black-Hole Spin Zachariah Etienne, Yuk Tung Liu, Stuart Shapiro, Thomas Baumgarte Binary black hole-neutron star (BHNS) binary mergers are candidate engines for both short-hard gamma-ray bursts and detectable gravitational radiation. Using our most recent conformal thin-sandwich BHNS initial data and our fully GR hydrodynamics code, which is now AMR-capable, we are able to simulate these binaries accurately through inspiral, merger, and ringdown. We explore the effects of BH spin (aligned and anti-aligned with the orbital angular momentum) by evolving binaries with BH:NS mass ratio $q=3$ that are nearly identical, except the BH spin is varied between $a/M_{\rm BH}=-0.5$ (anti-aligned) to 0.75. The number of orbits before merger increases with $a/M_{\rm BH}$. We also study the nonspinning BH case in depth, varying $q$ between 1, 3, and 5. Gravitational waveforms are calculated and compared to binary BH waveforms. Only a small disk ($< 0.01M_{\odot}$) forms for the anti-aligned spin case ($a/M_{\rm BH}=-0.5$) and for the largest mass ratio case ($q=5$). By contrast, a massive ($M_{disk}\approx 0.2M_{\odot}$), hot disk forms in the rapidly spinning $a/M_{\rm BH}=0.75$ aligned BH case. Such a disk could drive a SGRB, possibly by, e.g., producing a copious flux of $\nu-\bar{\nu}$ pairs. [Preview Abstract] |
Monday, May 4, 2009 4:54PM - 5:06PM |
T11.00008: Multipolar analysis of a binary black hole merger Robert Owen A definition of source multipoles, applicable on dynamical horizons, is given and applied to studying the ringdown of the remnant of a binary black hole merger. With this method, it is shown in detail that the angular structure of the acquiescent hole is the same as that of a Kerr horizon of the same mass and spin. [Preview Abstract] |
Monday, May 4, 2009 5:06PM - 5:18PM |
T11.00009: Null Geodesics as a Tool to Analyze Properties of Spacetimes in Numerical Relativity Randy Wolfmeyer, Jian Tao, Hui-Min Zhang, Wai-mo Suen We analyze the properties of a spacetime in terms of measurable physical quantities through the construction of null geodesics. The technique enables the comparison of spacetimes independent of the choices of time slicings and spatial coordinates used in the numerical construction. We apply the technique to study the accuracy of the quasi-equilibrium approximation of neutron star binaries. The phase of the inspiraling binary as observed at infinity and the distance between the two stars are constructed with null geodesics. We determine the minimum separation required for the quasi-equilibrium conformally flat assumptions to yield astrophysically realistic initial data for irrotational binary neutron star systems. [Preview Abstract] |
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