Black hole-neutron star mergers using a survey of finite-temperature equations of state

Abstract

Each of the potential signals from a black hole–neutron star merger should contain an imprint of the neutron star equation of state: gravitational waves via its effect on tidal disruption, the kilonova via its effect on the ejecta, and the gamma-ray burst via its effect on the remnant disk. These effects have been studied by numerical simulations and quantified by semianalytic formulas. However, most of the simulations on which these formulas are based use equations of state without finite temperature and composition-dependent nuclear physics. In this paper, we simulate black hole–neutron star mergers varying both the neutron star mass and the equation of state, using three finite-temperature nuclear models of varying stiffness. Our simulations largely vindicate formulas for ejecta properties but do not find the expected dependence of disk mass on neutron star compaction. We track the early evolution of the accretion disk, largely driven by shocking and fallback inflow, and do find notable equation-of-state effects on the structure of this early-time, neutrino-bright disk.