Influence of stellar compactness on finite-temperature effects in neutron star merger simulations

TL;DR

This study investigates how the initial compactness of neutron stars affects the thermal properties and gravitational wave signals in neutron star merger simulations, highlighting the importance of the finite-temperature EoS and particle effective mass models.

Contribution

It introduces a phenomenological model of the particle effective mass to analyze the impact of thermal prescriptions on merger outcomes across different stellar compactness levels.

Findings

Peak gravitational wave frequencies vary by up to 190 Hz with different thermal models.

Total ejecta is generally weakly affected by thermal prescription, but specific parameter choices can enhance ejecta.

Initial stellar compactness influences the thermal properties and gravitational wave signatures in mergers.

Abstract

Binary neutron star mergers probe the dense-matter equation of state (EoS) across a wide range of densities and temperatures, from the cold conditions of the inspiral to the high-temperature matter of the massive neutron star remnant. In this paper, we explore the sensitivity of neutron star mergers to uncertainties in the finite-temperature part of the EoS with a series of merger simulations performed in full general relativity. We expand on our previous work to explore the interplay between the thermal prescription and the stiffness of the zero-temperature EoS, which determines the compactness of the initial neutron stars. Using a phenomenological model of the particle effective mass, $M^*$, to calculate the finite-temperature part of the EoS, we perform merger simulations for a range of thermal prescriptions, together with two cold EoSs that predict either compact or large-radius initial neutron stars. We report on how the choice of $M^*$-parameters influences the thermal properties of the post-merger remnant, and how this varies for stars with different initial stellar compactness. We characterize the post-merger gravitational wave signals, and find differences in the peak frequencies of up to 190 Hz depending on the choice of $M^*$-parameters. Finally, we find that the total dynamical ejecta is in general only weakly sensitive to the thermal prescription, but that a particular combination of $M^*$-parameters, together with a soft cold EoS, can lead to significant enhancements in the ejecta.