Black hole-neutron star mergers with a hot nuclear equation of state: Outflow and neutrino-cooled disk for a low-mass, high-spin case

Abstract

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 (EOS) 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 MO neutron star, 5.6 MO black hole), high-spin (black hole J/M 2 = 0.9) system with the K0 = 220 MeV Lattimer-Swesty EOS. We find that about 0.08 MO of nuclear matter is ejected from the system, while another 0.3 MO forms a hot, compact accretion disk. The primary effects of the escaping neutrinos are (1) to make the disk much denser and more compact, (2) to cause the average electron fraction Y e of the disk to rise to about 0.2 and then gradually decrease again, and (3) to gradually cool the disk. The disk is initially hot (T ∼ 6 MeV) and luminous in neutrinos (Lν ∼ 1054 erg s -1), but the neutrino luminosity decreases by an order of magnitude over 50 ms of post-merger evolution. © 2013. The American Astronomical Society. All rights reserved.