* Astronomy

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.

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