Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session G8: General Relativistic Magnetohydrodynamical Simulations |
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Sponsoring Units: GGR DCOMP Chair: Joshua Faber, Rochester Institute of Technology Room: Embassy B |
Sunday, April 1, 2012 8:30AM - 9:06AM |
G8.00001: GRMHD Simulations of Astrophysical Phenomena Invited Speaker: Joshua Faber The field of numerical relativity has made great progress in the past several years, driven by advances in numerical techniques and computing resources. Here, we review progress made in general relativistic magnetohydrodynamics (GRMHD) simulations, which have been used to study merging binaries containing neutron stars, accretion disks around black holes and the production of jets, and stellar collapse, among other topics. We describe how GRMHD calculations have helped to reshape our understanding of the evolutionary progression of binary mergers and indicate why such sources are likely short gamma-ray burst candidates, how accretion disk models have shed light on many of the longstanding theoretical questions about such systems, and how collapse calculations have demonstrated the nature of the instabilities that lead to explosions. We also discuss the current state of the numerical techniques that have been created and implemented, and describe active research into expanding the science reach of numerical simulations, with an eye toward the next generation of numerical simulations that will incorporate physically realistic equations of states and nuclear models, as well as electromagnetic radiation and neutrino production. [Preview Abstract] |
Sunday, April 1, 2012 9:06AM - 9:18AM |
G8.00002: Magnetized Accretion onto Inspiraling Binary Black Holes: I. Spacetime Metric Bruno Mundim, Hiroyuki Nakano, Scott Noble, Manuela Campanelli, Yosef Zlochower, Julian Krolik, Nicolas Yunes Fully general relativistic numerical solutions to magnetized accretion onto black hole binaries are computationally very expensive. Current efforts are limited to very short binary separations. On the other extreme, however, point-particle Newtonian mechanics is used to accurately model accretion onto binaries with very large separations. In order to bridge the gap between these two extreme regimes, we construct a global time-dependent analytic approximation to the binary spacetime metric by asymptotically matching analytic metric approximations with different regions of validity. We apply black hole perturbation theory in the inner zone; 2.5 post-Newtonian theory in the near zone; and post-Minkowskian theory consistent with post-Newtonian theory in the far zone. In addition, we employ 3.5 post-Newtonian equations of motion to accurately describe the binary dynamics in its inspiral phase. We find the spacetime to be accurate to the expected leading post-Newtonian order, and demonstrate its reasonably small violations of the Hamiltonian and momentum constraints. [Preview Abstract] |
Sunday, April 1, 2012 9:18AM - 9:30AM |
G8.00003: Magnetized Accretion onto Inspiraling Binary Black Holes: II. Disk Dynamics Scott Noble, Bruno Mundim, Hiroyuki Nakano, Julian Krolik, Manuela Campanelli, Yosef Zlochower, Nicolas Yunes The coincident observation of electromagnetic and gravitational wave signals from supermassive black hole (BH) mergers would provide a bounty to physics: e.g., a new redshift-distance measurement, improved source localization, and tighter constraints on source parameters (e.g., BH masses, BH spins, disk characteristics). Previous simulation work has focused on the two extremes: very close to merger where numerical relativity is required, or at large binary separations where Newtonian gravity theory is accurate. Our work here investigates an intermediate regime, where the post-Newtonian (PN) approximation is valid yet close enough so that separation shrinkage timescale is comparable to matter inflow timescales. With our PN gravity model, we evolve a magnetized disk using a modern general relativistic magnetohydrodynamics code. We will show that many aspects of the disk follow the binary inward as its separation diminishes up until when the binary shrinkage timescale becomes smaller than the inflow timescale at the inner edge of the disk. We will also present predictions for the bolometric luminosity using our radiative cooling function as a proxy for emissivity. [Preview Abstract] |
Sunday, April 1, 2012 9:30AM - 9:42AM |
G8.00004: GR Simulations of Binary Black Hole Mergers in Magnetized Disks Brian Farris, Vasileios Paschalidis, Roman Gold, Stuart Shapiro Binary black hole mergers in circumbinary gaseous accretion disks are prime candidates for simultaneous observations of both gravitational and electromagnetic waves. We study such systems using our fully general relativistic magnetohydrodynamics code. We determine the quasi-equilibrium structure of a magnetized disk prior to binary-disk decoupling and track the dynamical evolution of the disk thereafter. We sketch recent developments in our study, which focuses on the final stages of binary black hole merger and the dynamical response of the disk. We discuss accretion onto the black holes during their late inspiral and merger and calculate the optically thin electromagnetic radiation as a perturbation. We identify characteristic, observable changes in the ``precursor'' and ``aftermath'' electromagnetic luminosity at merger. [Preview Abstract] |
Sunday, April 1, 2012 9:42AM - 9:54AM |
G8.00005: Supermassive Black Hole Mergers in Magnetized Hot Accretion Flows Tanja Bode, Pablo Laguna Electromagnetic emissions from gravitational wave sources such as supermassive black hole binaries will carry additional information of the environment in which the source is embedded. Using general relativistic simulations of tenuous gas on a supermassive binary's dynamic spacetime, we probe the regime where the strongest spacetime dynamics occur. Previous studies have shown supermassive black hole mergers in hot accretion flows to be accompanied by a robust pre-merger flare in bremsstrahlung emission, stemming from luminous density wakes and interbinary gas concentration, with an abrupt post-merger shut-off. Larger-scale simulations of galactic nuclei leave a gap in our understanding for the initial state of the gas several orbits before merger. We present results from the next step in the general relativistic study of electromagnetic counterparts to supermassive binary black hole mergers in hot accretion flows: binaries embedded in magnetized hot accretion flows. [Preview Abstract] |
Sunday, April 1, 2012 9:54AM - 10:06AM |
G8.00006: General Relativistic Simulations of Magnetized Plasmas around Merging Supermassive Black Holes Bruno Giacomazzo, John Baker, M. Coleman Miller, Christopher Reynolds, James van Meter Coalescing supermassive black hole binaries are produced by the mergers of galaxies and they are among the most powerful sources of gravitational waves that can be detected by space gravitational observatories. In many cases it is believed that the merger of supermassive black holes may happen in presence of matter and magnetic fields and in this case the gravitational wave signal may be accompanied by an electro-magnetic counterpart. We present the first general relativistic simulations of a magnetized plasma around merging supermassive black holes using the general relativistic magnetohydrodynamic code Whisky. By considering different magnetic field strengths, going from non-magnetically dominated to magnetically dominated regimes, we explore how magnetic fields affect the dynamics of the plasma and the possible emission of electromagnetic signals. [Preview Abstract] |
Sunday, April 1, 2012 10:06AM - 10:18AM |
G8.00007: Modeling the Electromagnetic and Gravitational Radiation from Neutron Stars Steven Liebling, Matthew Anderson, Eric Hirschmann, David Neilsen, Chad Hanna, Luis Lehner, Carlos Palenzuela, Christopher Thompson, Patrick Motl The dynamics of magnetized neutron stars both in binaries and in isolation are modeled with a novel numerical approach able to capture the dynamics of the star(s) and of the surrounding plasma. The stellar dynamics incorporate ideal MHD which appropriately models the regime in which the fluid pressure dominates that of the magnetic field, while the stellar exterior is modeled within the force free approach (magnetic pressure largely dominates that of the fluid). The approach is shown to approach certain known solutions. An intense electromagnetic outburst is observed for the collapsing, rotating star. The approach is also applied to the coalescence of a neutron star binary. [Preview Abstract] |
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