Hybrid equation of state approach in binary neutron-star merger simulations

TL;DR

This paper explores the effectiveness of hybrid equations of state with an approximate thermal treatment in simulating binary neutron-star mergers, comparing different models and identifying optimal parameters for realistic outcomes.

Contribution

It introduces a new finite-temperature equation of state and evaluates how different choices of the thermal adiabatic index influence simulation results.

Findings

Optimal thermal adiabatic index is approximately 1.7 for realistic simulations.

Hybrid equations of state can effectively approximate full finite-temperature models.

Differences between hybrid and full models impact gravitational-wave signals and remnant properties.

Abstract

We investigate the use of hybrid equations of state in binary neutron-star simulations in full general relativity, where thermal effects are included in an approximate way through the adiabatic index $\Gamma_{\rm{th}}$. We employ a newly developed finite-temperature equation of state derived in the Brueckner-Hartree-Fock approach and carry out comparisons with the corresponding hybrid versions of the same equation of state, investigating how different choices of $\Gamma_{\rm{th}}$ affect the gravitational-wave signal and the hydrodynamical properties of the remnant. We also perform comparisons with the widely used SFHo equation of state, detailing the differences between the two cases. Overall, we determine that when using a hybrid equation of state in binary neutron-star simulations, the value of thermal adiabatic index $\Gamma_{\rm{th}} \approx 1.7$ best approximates the dynamical and thermodynamical behaviour of matter computed using complete, finite-temperature equations of state.