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

TL;DR

This paper investigates black hole-neutron star mergers using finite-temperature nuclear equations of state, revealing effects on ejecta and early disk structure, with implications for gravitational wave and electromagnetic signals.

Contribution

It introduces simulations with finite-temperature, composition-dependent nuclear physics, expanding beyond previous models that used simpler equations of state.

Findings

Ejecta properties largely match existing semi-analytic formulae.

No clear dependence of disk mass on neutron star compaction was observed.

Finite-temperature effects influence early disk structure and neutrino emission.

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 semi-analytic formulae. However, most of the simulations on which these formulae 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 formulae 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.