Published on Mon Nov 08 2021

General-relativistic neutrino-radiation magnetohydrodynamics simulation of black hole-neutron star mergers for seconds

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Seconds-long numerical-relativity simulations for black hole-neutron star mergers are performed for the first time to obtain a self-consistent picture of the merger and post-merger evolution processes. To investigate the case that tidal disruption takes place, we choose the initial mass of the black hole to be or with the dimensionless spin of 0.75. The neutron-star mass is fixed to be . We find that after the tidal disruption, dynamical mass ejection takes place spending together with the formation of a massive accretion disk. Subsequently, the magnetic field in the disk is amplified by the magnetic winding and magnetorotational instability, establishing a turbulent state and inducing the angular momentum transport. The post-merger mass ejection by the magnetically-induced viscous effect sets in at - after the tidal disruption, at which the neutrino luminosity drops below , and continues for several hundreds ms. A magnetosphere near the rotational axis of the black hole is developed after the matter and magnetic flux fall into the black hole from the accretion disk, and high-intensity Poynting flux generation sets in at a few hundreds ms after the tidal disruption. The intensity of the Poynting flux becomes low after the significant post-merger mass ejection, because the opening angle of the magnetosphere increases. The lifetime for the stage with the strong Poynting flux is -, which agrees with the typical duration of short-hard gamma-ray bursts.