Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session P14: Numerical Simulations of Black Holes and Neutron Stars |
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Sponsoring Units: GGR Chair: Roland Haas, Georgia Institute of Technology Room: Washington 4 |
Monday, February 15, 2010 10:45AM - 10:57AM |
P14.00001: Exploring the Magnetic field and Black Hole Spin in Black Hole--Neutron star mergers Sarvnipun Chawla, Matthew Anderson, Luis Lehner, Steven Liebling, Miguel Megevand, Patrick Motl, David Neilsen, Carlos Palenzuela A sizable magnetic field in neutron star-black hole binaries can have a strong influence on the merger dynamics of the fluid by redistributing angular momentum through different mechanisms. The magnetic field can also be responsible for collimating jets. BH spin can increase the number of orbits before merger as compared to a binary with a non-spinning BH. The corresponding decrease in ISCO can alter the tidal disruption suffered by the NS. We present results of fully relativistic black hole--neutron star simulations proceeding from quasi-circular initial data generated with the Lorene libraries. We explore the effect of magnetic field and spin by evolving four sets of nearly identical initial data which differ in their magnetic field and spin values. We examine the gravitational wave signature through direct simulation. Finally, we compare the fluid structure and explore the magnetic field configuration in the post-merger remnant disk. [Preview Abstract] |
Monday, February 15, 2010 10:57AM - 11:09AM |
P14.00002: Merger of white dwarf-neutron star binaries: Prelude to hydrodynamic simulations in general relativity Vasileios Paschalidis, Morgan MacLeod, Thomas W. Baumgarte, Stuart L. Shapiro White dwarf-neutron star binaries generate detectable gravitational radiation. We construct Newtonian equilibrium models of corotational white dwarf-neutron star (WDNS) binaries in circular orbit and find that these models terminate at the Roche limit. At this point the binary will undergo either stable mass transfer (SMT) and evolve on a secular time scale, or unstable mass transfer (UMT), which results in the tidal disruption of the WD. The path a given binary will follow depends primarily on its mass ratio. We analyze the fate of known WDNS binaries and use population synthesis results to estimate the number of LISA-resolved galactic binaries that will undergo either SMT or UMT. We model the quasistationary SMT epoch by solving a set of simple ordinary differential equations and compute the corresponding gravitational waveforms. Finally, we discuss in general terms the possible fate of binaries that undergo UMT. If sufficient WD debris lands on the NS, the remnant may collapse, whereby the gravitational waves from the inspiral, merger, and collapse phases will sweep from LISA through LIGO frequency bands. If the debris forms a disk about the NS, it may fragment and form planets. [Preview Abstract] |
Monday, February 15, 2010 11:09AM - 11:21AM |
P14.00003: Gravitational Waves from Magnetized Binary Neutron Star Mergers Bruno Giacomazzo, Luciano Rezzolla, Luca Baiotti Binary neutron stars are among the most important sources of gravitational waves which are expected to be detected by the current or next generation of gravitational wave detectors, such as LIGO and Virgo, and they are also thought to be at the origin of very important astrophysical phenomena, such as short gamma-ray bursts. In order to describe the dynamics of these events one needs to solve the full set of general relativistic magnetohydrodynamics equations through the use of parallel numerical codes. I will report on some recent results obtained with the use of the fully general relativistic magnetohydrodynamic code Whisky in simulating binary neutron stars which inspiral and merge forming an hypermassive neutron star which eventually collapses to form a black hole surrounded by a torus. I will in particular describe how the magnetic fields can affect the dynamics and consequently the gravitational waves emitted by these systems and discuss about their detectability by current and future gravitational-wave detectors. [Preview Abstract] |
Monday, February 15, 2010 11:21AM - 11:33AM |
P14.00004: Simulations of Black Hole-Neutron Star Binaries Francois Foucart, Matthew Duez, Lawrence Kidder, Saul Teukolsky We present simulations of black hole-neutron star binaries aimed at the determination of the relative importance of different initial parameters. Keeping a constant mass ratio of 1:3, we vary the radius of the star, the stiffness of the equation of state, and the magnitude and orientation of the black hole spin. We discuss differences in the tidal interactions and the characteristics of the long-lived accretion disk which eventually forms, and we describe how these differences influence the gravitational waves emitted by the system. Using eccentricity removal techniques, we also assess the effect of small deviations from circular orbits due to imperfections in the initial data. [Preview Abstract] |
Monday, February 15, 2010 11:33AM - 11:45AM |
P14.00005: Simulations of Neutron-Star Binaries using the Spectral Einstein Code (SpEC) Jeffrey Kaplan, Christian Ott, Curran Muhlberger, Matthew Duez, Francois Foucart, Mark Scheel Since the first successful fully general-relativistic simulations of coalescing neutron-star binaries, researchers have steadily improved the quality of their neutron-star binary evolutions with the goal of drawing connections between neutron-star physics (such as the NS equation of state, magnetic fields, etc.) and astrophysical observables (in the form of gravitational waves and the electromagnetic signature of short gamma-ray bursts). We present the progress of the Caltech-Cornell numerical relativity collaboration in simulating the merger of neutron star binaries. Our simulations employ a two-grid approach: on one grid we evolve the Einstein equations in the generalized harmonic formulation using pseudospectral methods, and on the other we solve the relativistic fluid equations using high-resolution shock-capturing techniques. In our presentation, we focus on results of long-term simulations of the coalescence, merger, and post-merger evolution of equal mass neutron-star binaries using a simple gamma law equation of state and discuss preliminary results from work towards including a microphysical finite-temperature nuclear equation of state and neutrino cooling. [Preview Abstract] |
Monday, February 15, 2010 11:45AM - 11:57AM |
P14.00006: Neutron Star-Spinning Black Hole Binary Mergers: Simulations in Full General Relativity 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, February 15, 2010 11:57AM - 12:09PM |
P14.00007: Constructing initial data for magnetized rotating and binary compact objects Charalampos Markakis, Koji Uryu, Eric Gourgoulhon We report work in progress towards a relativistic formulation for constructing magnetized rotating or binary neutron star initial data, in an ideal MHD approximation. The formulation involves a self-consistent scheme for solving the Einstein-Maxwell and MHD-Euler equations for systems with an approximate helical symmetry. Numerical codes based on this scheme are expected to model magnetars with non-axisymmetric magnetic fields as well as magnetized binary neutron star systems in quasi-equilibrium. [Preview Abstract] |
Monday, February 15, 2010 12:09PM - 12:21PM |
P14.00008: Near-extremal-spin Black Hole: New Initial Data and Evolution Yuk Tung Liu, Zachariah Etienne, Stuart Shapiro We present new initial data for rapidly spinning black holes (BHs) that can be evolved using the standard moving puncture technique. Unlike conformally-flat initial data, our initial data can produce a BH spin very close to the extreme Kerr limit. In addition, our initial data do not contain spurious gravitational waves for an isolated, spinning BH. We demonstrate that we can evolve both a stationary and boosted BH stably and accurately with a spin parameter as high as $a/M$=0.99. Initial data for compact binaries containing rapidly spinning BHs may be constructed using our proposed metric for the background conformal metric. Our simulations for single BHs suggest that such binary initial data can be evolved successfully by the moving puncture technique. [Preview Abstract] |
Monday, February 15, 2010 12:21PM - 12:33PM |
P14.00009: Extreme Black-Hole Binaries Yosef Zlochower, Carlos Lousto, Manuela Campanelli In this talk I will show recent results obtained by the RIT group from simulations of highly-spinning binaries, including new data that gives near maximal spins, and high-mass ratio binaries. Simulations in both of these regimes are numerically challenging. However, as astrophysical binaries are expected to be highly-spinning and have high mass ratios, accurate simulations in these regimes are crucial for understanding the dynamics of realistic binaries. [Preview Abstract] |
Monday, February 15, 2010 12:33PM - 12:45PM |
P14.00010: Looking at Black Holes Mathematically James Graber I will briefly discuss a mathematically exact relationship between the impact parameter at infinity and the photon orbit in the equatorial plane of the Kerr metric., originally derived by Bardeen in the early 1970s. Next I will present a mathematical generalization of this formula, and apply it to slightly perturbed Kerr metrics. If time permits I will compare the computed results with recent observations of Sgr A* performed by Doeleman \textit{et al}. [Preview Abstract] |
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