Black hole-neutron star mergers with massive neutron stars in numerical relativity

Abstract

We study the merger of black hole-neutron star (BH-NS) binaries in numerical relativity, focusing on the properties of the remnant disk and the ejecta, varying the mass of compactness of the NS and the mass and spin of the BH. We find that within the precision of our numerical simulations, the remnant disk mass and ejecta mass normalized by the NS baryon mass (M^rem and M^eje, respectively), and the cutoff frequency fcut normalized by the initial total gravitational mass of the system at infinite separation approximately agree among the models with the same NS compactness CNS=MNS/RNS, mass ratio Q=MBH/MNS, and dimensionless BH spin χBH irrespective of the NS mass MNS in the range of 1.092−1.691M⊙. This result shows that the merger outcome depends sensitively on Q, χBH, and CNS but only weakly on MNS. This justifies the approach of studying the dependence of NS tidal disruptions on the NS compactness by fixing the NS mass but changing the EOS. We further perform simulations with massive NSs of MNS=1.8M⊙, and compare our results of M^rem and M^eje with those given by existing fitting formulas to test their robustness for more compact NSs. We find that the fitting formulas obtained in the previous studies are accurate within the numerical errors assumed, while our results also suggest that further improvement is possible by systematically performing more precise numerical simulations. Published by the American Physical Society 2024