BLACK HOLE-NEUTRON STAR MERGERS WITH A HOT NUCLEAR EQUATION OF STATE: OUTFLOW AND NEUTRINO-COOLED DISK FOR A LOW-MASS, HIGH-SPIN CASE

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 M sub([middot in circle]) neutron star, 5.6 M sub([middot in circle]) black hole), high-spin (black hole J/M super(2) = 0.9) system with the K sub(0) = 220 MeV Lattimer-Swesty EOS. We find that about 0.08 M sub([middot in circle]) of nuclear matter is ejected from the system, while another 0.3 M sub([middot in circle]) 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 sub(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 (L sub([nu]) ~ 10 super(54) erg s super(-1)), but the neutrino luminosity decreases by an order of magnitude over 50 ms of post-merger evolution.