Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session K15: Numerical Relativity with Matter: Methods and Simulations I |
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Chair: Geoffrey Lovelace, California State University, Fullerton Room: 103 |
Sunday, April 6, 2014 1:30PM - 1:42PM |
K15.00001: Gravitational Waveforms in the Early Inspiral of Black Hole-Neutron Star Systems Kevin Barkett One of the target systems for gravitational wave detection by aLIGO is a black hole-neutron star (BHNS) binary. For moderate to large black-hole spins, different post-Newtonian approximants disagree for BHNS systems even early in the inspiral, necessitating accurate yet computationally expensive numerical relativity simulations that cover many orbits in the inspiral regime. Because matter and tidal effects are expected to influence the system only when the two bodies are extremely close together, I simulate binary black hole systems of mass ratio 7 as a proxy for BHNS systems during inspiral. I will carry out numerical relativity simulations, keeping the smaller (``neutron star'') object spinless testing various spins on the larger black hole. These waveforms will be compared with the post-Newtonian approximants to analyze the robustness of hybridizing long numerical relativity waveforms with post-Newtonian ones to generate long gravitational waveforms which cover the full aLIGO frequency band. [Preview Abstract] |
Sunday, April 6, 2014 1:42PM - 1:54PM |
K15.00002: Black hole-neutron star mergers with a hot equation of state and neutrino cooling Francois Foucart Black hole-neutron star (BHNS) and neutron star-neutron star mergers will be prime candidates for the joint detection of gravitational wave and electromagnetic (EM) signals once the Advanced LIGO/VIRGO/KAGRA detectors come online. For BHNS binaries, the result of the merger strongly depends on the parameters of the system. EM emissions from a post-merger disk (e.g. gamma-ray bursts) are only possible for low mass or high spin black holes. The amount of ejected neutron-rich material, which has important consequences for the emission of more isotropic EM signals and the production of r-process elements, can also vary by a few orders of magnitudes - with high mass, high spin black holes ejecting more than $0.1M_\odot$ of unbound material. I will describe recent simulations of BHNS mergers performed by the SXS collaboration, which explore the parameter space dependence of these mergers while using a hot nuclear equation of state (LS220) and approximate neutrino cooling of the post-merger accretion disk. I will discuss the qualitative differences between these mergers and earlier simulations performed with polytropic equations of state, as well as the effect of neutrino cooling on the post-merger evolution and the general properties of the neutrino radiation. [Preview Abstract] |
Sunday, April 6, 2014 1:54PM - 2:06PM |
K15.00003: Neutrino-Driven Outflows From Realistic Black Hole-Neutron Star Mergers M. Brett Deaton, Francois Foucart, Matthew D. Duez, Evan O'Connor, Christian D. Ott, Lawrence E. Kidder, Curran D. Muhlberger, Harald P. Pfeiffer, Mark A. Scheel, Bela Szilagyi A gamma ray burst requires a relativistic outflow of low-density plasma, a likely outcome of black hole-neutron star mergers with remnant disks. We continue our study into the neutrino-driven outflows from realistic merger scenarios (7 $M_{\odot}$-10 $M_{\odot}$ black holes with high spin) by examining disks formed in general relativistic simulations using the LS220 equation of state and neutrino leakage. I will focus on the neutrino radiation properties of the disks including luminosities, optical depths, and annihilation efficiencies. [Preview Abstract] |
Sunday, April 6, 2014 2:06PM - 2:18PM |
K15.00004: Mass ejection from black hole-neutron star binaries Koutarou Kyutoku, Kunihito Ioka, Masaru Shibata Black hole-neutron star binaries are ones of the most promising sources of gravitational waves for upcoming second-generation detectors. To confirm gravitational-wave detection and obtain as much information as possible, it is desirable to observe electromagnetic counterparts simultaneously. It has been pointed out by many authors that various electromagnetic signals are reasonably expected if substantial material is ejected during the binary merger. One plausible mechanism of mass ejection from black hole-neutron star binaries is tidal disruption of neutron stars by the tidal force exerted by black holes. A quantitative study of this dynamical mass ejection requires numerical-relativity simulations. We perform simulations of black hole-neutron star binaries focusing on the dynamical mass ejection for a range of binary parameters including equations of state of neutron star matter. We present important results such as masses and velocities of ejecta obtained by our simulations, and also discuss possible characteristics of electromagnetic counterparts to black hole-neutron star binaries. In particular, we focus on anisotropy and bulk velocity (i.e., the velocity component other than the expansion velocity) of the ejecta, and electromagnetic features resulting from them. [Preview Abstract] |
Sunday, April 6, 2014 2:18PM - 2:30PM |
K15.00005: GR simulations of binary black hole-neutron stars: Precursor electromagnetic signals Vasileios Paschalidis, Zachariah B. Etienne, Stuart L. Shapiro We present a new computational method for smoothly matching general relativistic ideal magnetohydrodynamics (MHD) to its force-free limit. The method is based on a flux-conservative formalism for MHD and its force-free limit, and a vector potential formulation for the induction equation to maintain the zero divergence constraint for the magnetic field. The force-free formulation evolves the magnetic field and the Poynting vector. Our force-free code passes a robust suite of tests, performed both in 1D flat spacetime and in 3D curved (black hole) spacetimes. Our matching technique successfully reproduces the aligned rotator force-free solution. As an application, we performed the first general relativistic, force-free simulations of neutron star (NS) magnetospheres in orbit about spinning and non-spinning black holes with BH:NS mass ratio 3:1. We find promising precursor EM emission: typical Poynting luminosities at, e.g., an orbital separation of 6.6 times the NS radius, are $L \sim 6 \times 10^{42}$erg/s for a $1.4M_\odot$ NS endowed with a dipolar magnetic field with polar strength $10^{13}$G. The Poynting flux peaks within a broad beam of ~40 degrees in the azimuthal direction, establishing a possible lighthouse effect. [Preview Abstract] |
Sunday, April 6, 2014 2:30PM - 2:42PM |
K15.00006: General relativistic corrections to the pulsar spin-down luminosity Milton Ruiz, Vasileios Paschalidis, Stuart Shapiro Pulsar magnetospheres are typically modeled in flat spacetime. Adopting our new method for smoothly matching general relativistic ideal magnetohydrodynamics to its force-free limit, we perform the first systematic study of pulsar magnetospheres in general relativity. We endow the neutron star with a general relativistic dipole magnetic field, and model the dense interior with ideal magnetohydrodynamics, and assume force-free electrodynamics in the exterior. Normalizing the spin-down luminosity by its corresponding Minkwoski value, we find that relativistic effects give rise to a modest enhancement: the maximum enhancement for $n=1$ polytropes is $\sim 23\%$, and for a rapidly rotating $n=0.5$ polytrope we find an enhancement of $\sim 35\%$. We expect stiffer equation of state and more rapidly rotating neutron stars to lead to even larger enhancements in the spin-down luminosity. [Preview Abstract] |
Sunday, April 6, 2014 2:42PM - 2:54PM |
K15.00007: Tidal disruption process for a Newtonian star and non-spinning black hole Roseanne Cheng, Tamara Bogdanovic In this study, we analyze the tidal process which disrupts a Newtonian star on a parabolic orbit about a non-spinning black hole and places the debris on bound and unbound trajectories. We implement a three dimensional hydrodynamics and self-gravity code which also calculates the relativistic tidal interaction in a local moving frame centered on a star. We characterize the mass tidally stripped from the star and estimate the orbital parameters of the debris by local to black hole frame transformations. We discuss the bound and unbound ``kicks'' to the star off of its initial orbit in weak and partially disruptive encounters. We show super-Eddington return rates of debris which closely follow the canonical $t^{-5/3}$ fall-off. We also show results of encounters very close to the black hole ($\alt 10M$) and discuss the relativistic effects early in the return rate. [Preview Abstract] |
Sunday, April 6, 2014 2:54PM - 3:06PM |
K15.00008: Simulating extreme-mass-ratio systems in full general relativity: tidal disruption events William East, Frans Pretorius Sparked by recent and anticipated observations, there is considerable interest in understanding events where a star is tidally disrupted by a massive black hole. Motivated by this and other applications, we introduce a new method for numerically evolving the full Einstein field equations in situations where the spacetime is dominated by a known background solution. The technique leverages the knowledge of the background solution to subtract off its contribution to the truncation error, thereby more efficiently achieving a desired level of accuracy. We demonstrate how the method can be applied to systems consisting of a solar-type star and a supermassive black hole with mass ratios $\geq 10^6$. The self-gravity of the star is thus consistently modelled within the context of general relativity, and the star's interaction with the black hole computed with moderate computational cost, despite the over five orders of magnitude difference in gravitational potential (as defined by the ratio of mass to radius). We study the tidal deformation of the star during infall, as well as the gravitational wave emission, and discuss ongoing work to understand the importance of strong-field gravity effects on tidal disruption events. [Preview Abstract] |
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