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TOPIC: Coalescing Black Hole-Neutron Star Binaries

Blobrana

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Posts: 131433

Date: Apr 13 08:18 2013

Black Hole-Neutron Star Mergers	Permalink

Title: Black Hole-Neutron Star Mergers with a Hot Nuclear Equation of State: Outflow and Neutrino-Cooled Disk for a Low-Mass, High-Spin Case Authors: M. Brett Deaton, Matthew D. Duez, Francois Foucart, Evan O'Connor, Christian D. Ott, Lawrence E. Kidder, Curran D. Muhlberger, Mark A. Scheel, Bela Szilagyi Neutrino emission significantly affects the evolution of the accretion tori formed in black hole-neutron star mergers. It removes energy from the disk, alters its composition, and provides a potential power source for a gamma-ray burst. To study these effects, simulations in general relativity with a hot microphysical equation of state and neutrino feedback are needed. We present the first such simulation, using a neutrino leakage scheme for cooling to capture the most essential effects and considering a moderate mass (1.4 solar mass neutron star, 5.6 solar mass black hole), high spin (black hole J/M²=0.9) system with the K_0=220 MeV Lattimer-Swesty equation of state. We find that about 0.08 solar masses of nuclear matter is ejected from the system, while another 0.3 solar masses forms a hot, compact accretion disk. The primary effects of the escaping neutrinos are (i) to make the disk much denser and more compact, (ii) to cause the average electron fraction Y_e of the disk to rise to about 0.2 and then gradually decrease again, and (iii) to gradually cool the disk. The disk is initially hot (T~6 MeV) and luminous in neutrinos (L_{\nu}~10^{54} erg s^{-1}), but the neutrino luminosity decreases by an order of magnitude over 50 ms of post-merger evolution. Read more (628kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Oct 3 22:19 2012

Neutron Star - Black Hole Binaries	Permalink

Title: Periastron Advance in Neutron Star - Black Hole Binaries Authors: Manjari Bagchi As neutron star - black hole binaries are expected to be discovered through future pulsar surveys using upcoming facilities, it is necessary to understand various observable properties of such systems. In the present work, we study the advance of the periastron of such binaries under the post-Newtonian formalism over a wide range of parameters. We find that the first and second order post-Newtonian effects and the leading order spin-orbit coupling effects are significant for such binaries but higher order effects can be neglected. Read more (526kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Sep 2 10:58 2012

Coalescing Black Hole-Neutron Star Binaries	Permalink

Title: The Black Hole Remnant of Black Hole-Neutron Star Coalescing Binaries Authors: Francesco Pannarale We present a model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with parallel orbital angular momentum and initial black hole spin. This approach is based on the Buonanno, Kidder, and Lehner method for binary black holes and it is successfully tested against the results of numerical-relativity simulations: the dimensionless spin parameter is predicted with absolute error \lesssim 0.02, whereas the relative error on the final mass is \lesssim 2%, its distribution being pronouncedly peaked at 1%. Our approach and the fit to the torus remnant mass reported in Foucart (2012) thus constitute an easy-to-use analytical model that accurately describes the remnant of BH-NS mergers. We investigate the space of parameters consisting of the binary mass ratio, the initial black hole spin, and the neutron star mass and equation of state. We provide indirect support to the cosmic censorship conjecture for black hole remnants of black hole-neutron star mergers. We show that the presence of a neutron star affects the quasi-normal mode frequency of the black hole remnant, thus suggesting that the ringdown epoch of the gravitational wave signal may virtually be used to (1) distinguish binary black hole from black hole-neutron star mergers and to (2) constrain the neutron star equation of state. Read more (3243kb, PDF) __________________

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