Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session G14: Simulations of Binary Neutron Star and Black Hole - Neutron Star Mergers |
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Sponsoring Units: GGR Chair: Andrew MacFadyen, New York University, New York Room: Plaza Court 3 |
Sunday, April 14, 2013 8:30AM - 8:42AM |
G14.00001: General relativistic simulations of black hole-neutron star mergers: Effects of tilted magnetic fields Zachariah Etienne, Vasileios Paschalidis, Stuart Shapiro Black hole--neutron star (BHNS) binary mergers can form disks in which magnetorotational instability (MRI)-induced turbulence may drive accretion onto the remnant BH, supporting relativistic jets and providing the engine for a short-hard gamma-ray burst (SGRB). Our earlier magnetized BHNS simulations showed that tidal disruption winds the NS internal magnetic fields into a toroidal configuration, with poloidal fields so weak that capturing MRI with full-disk simulations would require $\sim$10$^8$ CPU-hours. In that study we imposed equatorial symmetry, suppressing poloidal magnetic fields that might be generated from plasma crossing the orbital plane. Here we show that tilting the initial poloidal magnetic fields in the NS generates much stronger poloidal fields in the disk, indicating that asymmetric initial conditions may be necessary for establishing BHNS mergers as SGRB progenitors via fully general relativistic MHD simulations. We demonstrate that BHNS mergers may form an SGRB engine when the remnant disk from an unmagnetized BHNS simulation is seeded with purely poloidal fields dynamically unimportant initially, but strong enough to resolve MRI. Magnetic turbulence occurs in the disk, driving accretion and supporting Poynting-dominated jet outflows sufficent to power an SGRB. [Preview Abstract] |
Sunday, April 14, 2013 8:42AM - 8:54AM |
G14.00002: Black hole-neutron star mergers at realistic mass ratios Francois Foucart, Brett Deaton, Matthew Duez, Lawrence Kidder, Ilana MacDonald, Christian Ott, Harald Pfeiffer, Mark Scheel, Bela Szilagyi, Saul Teukolsky Black hole-neutron star mergers resulting in the disruption of the neutron star and the formation of an accretion disk and/or the ejection of unbound material are prime candidates for the joint detection of gravitational-wave and electromagnetic signals. Whether the disruption of the neutron star occurs or not depends on the parameters of the binary, and particularly on the mass ratio, the black hole spin, and the neutron star equation of state. The characteristics of the merger remnant, and thus of any post-merger electromagnetic signal, also vary widely with the parameters of the binary. Numerical simulations of black hole-neutron star mergers have generally considered fairly low mass black holes (M$<$7M$_{sun}$), even though higher masses are favored by both population synthesis models and observations of X-ray binaries. In this talk, we will discuss numerical results for higher mass black holes (M$\sim$10M$_{sun}$), and in particular the conditions under which the neutron star disrupts, the ejection of unbound material, and the effects of both the neutron star radius and the black hole spin on the gravitational wave signal and the characteristics of the post-merger remnant. [Preview Abstract] |
Sunday, April 14, 2013 8:54AM - 9:06AM |
G14.00003: Neutrino Energetics of Black Hole--Neutron Star Mergers M. Brett Deaton We present simulations of black hole--neutron star mergers solving the coupled Einstein-hydrodynamics equations, including radiative cooling and chemical evolution. To this end we have added a leakage approximation to the Spectral Einstein Code (SpEC). The nuclear matter is modeled by the Lattimer \& Swesty equation of state. This first in a set of binary configurations uses a low mass ratio ($q=4$) and high spin ($a=0.9$). Our choice of parameters is astrophysically optimistic and provides an approximate upper bound on radiation energetics due to the large (initial mass $\sim 0.15 M_\odot$), long-lived ($>150$ ms) disk. We examine the energy of neutrino radiation, the dynamics of the remnant disk, and the characteristics of the tidally ejected fluid. [Preview Abstract] |
Sunday, April 14, 2013 9:06AM - 9:18AM |
G14.00004: Black hole - neutron star simulations with Bowen-York type data Pablo Laguna, Michael Clark, Tanja Bode, Deirdre Shoemaker, Carl Rodriguez We introduce an approach for the construction of initial data representing black hole - neutron star binaries based on Bowen-York type solutions to the momentum constraint that account for the presence of matter sources. We demonstrate the effectiveness of this initial data approach with results from simulations of mixed binary systems that include estimates of gravitational wave emission. [Preview Abstract] |
Sunday, April 14, 2013 9:18AM - 9:30AM |
G14.00005: Initial Data for Binary Neutron Stars with Arbitrary Spin and Orbital Eccentricity Petr Tsatsin, Pedro Marronetti The starting point of any general relativistic numerical simulation is a solution of the Hamiltonian and momentum constraint. One characteristic of the Binary Neutron Star (BNS) initial data problem is that, unlike the case of binary black holes, there are no formalisms that permit the construction of initial data for stars with arbitrary spins. For many years, the only options available have been systems either with irrotational or corotating fluid. Ten years ago, Marronetti \& Shapiro (2003) introduced an approximation that would produce such arbitrarily spinning systems. More recently, Tichy (2012) presented a new formulation to do the same. However, all these data sets are bound to have a non-zero eccentricity that results from the fact the stars' velocity have initial null radial components. We present here a new approximation for BNS initial data for systems that possess arbitrary spins and arbitrary radial and tangential velocity components. The latter allows for the construction of data sets with arbitrary orbital eccentricity. Through the fine-tuning of the radial component, we were able to reduce the eccentricity by a factor of several compared to that of standard helical symmetry data sets such as those currently used in the scientific community. [Preview Abstract] |
Sunday, April 14, 2013 9:30AM - 9:42AM |
G14.00006: Binary NS simulations using SpEC Roland Haas, Jeffrey Kaplan, Bela Szilagyi, Curran Muhlberger, Francois Foucart, Jonas Lippuner, Mark Scheel, Matthew Duez, Christian Ott NSNS binaries are expected to be one of the major sources of gravitational radiation detectable by Advanced LIGO. Together with neutrinos, gravitational waves are our only means to learn about the processes deep within a merging pair of NS, shedding light on the as yet poorly understood, equation of state governing matter at nuclear densities and beyond. We report on binary neutron star simulations using the Spectral Einstein Code (SpEC) developed by the Caltech-Cornell-CITA-WSU collaboration. We simulate the inspiral through many orbits, follow the post-merger evolution, and compute the full gravitational wave signal. We provide estimates on the accuracy required for the LIGO scientific goals of constraining EOS parameters. [Preview Abstract] |
Sunday, April 14, 2013 9:42AM - 9:54AM |
G14.00007: Binary neutron stars with arbitrary spins in numerical relativity Nick Tacik, Francois Foucart, Harald Pfeiffer Among numerical relativity simulations of binary neutron star inspirals, spin remains one of the least explored parameters. The motivation for such simulations is presented, as well as results for the construction of initial data for neutron stars with arbitrary spins, including the measurement of the stars' intrinsic angular momenta. Preliminary results of the evolution of spinning binaries will also be discussed. [Preview Abstract] |
Sunday, April 14, 2013 9:54AM - 10:06AM |
G14.00008: Loud and Bright: Gravitational and possible electromagnetic signals induced by binary neutron star mergers Carlos Palenzuela, Luis Lehner, Marcelo Ponce, Chris Thompson, Steve Liebling, Dave Neilsen, Eric Hirschmann, Matt Anderson, Patrick Motl Our main goal is to investigate how the strongly gravitating and highly dynamical behavior of magnetized binary neutron stars can affect the plasma in the magnetosphere in such a way that powerful electromagnetic emissions can be induced, as well as stressing its connection with gravitational waves produced by the system. Such phenomena is a natural candidate for bright (EM) and loud (GW) emissions, as pulsars are strong electromagnetic emitters on one hand, and merging binary neutron stars are powerful sources of gravitational radiation. [Preview Abstract] |
Sunday, April 14, 2013 10:06AM - 10:18AM |
G14.00009: Importance of cooling in triggering the collapse of hypermassive neutron stars Vasileios Paschalidis, Zachariah Etienne, Stuart Shapiro The inspiral and merger of a binary neutron star (NSNS) can lead to the formation of a hypermassive neutron star (HMNS). As the HMNS loses thermal pressure due to neutrino cooling and/or centrifugal support due to gravitational wave (GW) emission, and/or magnetic breaking of differential rotation it will collapse to a black hole. To assess the importance of shock-induced thermal pressure and cooling, we adopt an idealized equation of state and perform NSNS simulations in full GR through late inspiral, merger, and HMNS formation, accounting for cooling. We show that thermal pressure contributes significantly to the support of the HMNS against collapse and that thermal cooling accelerates its ``delayed'' collapse. Our simulations demonstrate explicitly that cooling can induce the catastrophic collapse of a hot hypermassive neutron star formed following the merger of binary neutron stars. Thus, cooling physics is important to include in NSNS merger calculations to accurately determine the lifetime of the HMNS remnant and to extract information about the NS equation of state, cooling mechanisms, bar instabilities and B-fields from the GWs emitted during the transient phase prior to BH formation. [Preview Abstract] |
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