Black hole-neutron star binary merger: Dependence on black hole spin orientation and equation of state

We systematically performed numerical-relativity simulations for black hole-neutron star (BH-NS) binary mergers with a variety of the BH spin orientation and nuclear-theory-based equations of state (EOS) of the NS. The initial misalignment angles of the BH spin measured from the direction of the orbital angular momentum are chosen in the range of itilt,0≈30°-90°. We employed four models of nuclear-theory-based zero-temperature EOS for the NS in which the compactness of the NS is in the range of C=MNS/RNS=0.138-0.180, where MNS and RNS are the mass and the radius of the NS, respectively. The mass ratio of the BH to the NS, Q=MBH/MNS, and the dimensionless spin parameter of the BH, χ, are chosen to be Q=5 and χ=0.75, together with MNS=1.35M so that the BH spin misalignment has a significant effect on tidal disruption of the NS. We obtain the following results: (i) The inclination angles of itilt,0<70° and itilt,0<50° are required for the formation of a remnant disk with its mass larger than 0.1M for the cases C=0.140 and C=0.160, respectively, while the disk mass is always smaller than 0.1M for C0.175. The ejecta with its mass larger than 0.01M is obtained for itilt,0<85° with C=0.140, for itilt,0<65° with C=0.160, and for itilt,0<30° with C=0.175. (ii) The rotational axis of the dense part of the remnant disk with its rest-mass density larger than 109g/cm3 is approximately aligned with the remnant BH spin for itilt,0≈30°. On the other hand, the disk axis is misaligned initially with ∼30° for itilt,0≈60°, and the alignment with the remnant BH spin is achieved at ∼50-60ms after the onset of merger. The accretion time scale of the remnant disk is typically ∼100ms and depends only weakly on the misalignment angle and the EOS. (iii) The ejecta velocity is typically ∼0.2-0.3c and depends only weakly on the misalignment angle and the EOS of the NS, while the morphology of the ejecta depends on its mass. (iv) The gravitational-wave spectra contains the information of the NS compactness in the cutoff frequency for itilt,0?60°.