Effects of the microphysical Equation of State in the mergers of magnetized Neutron Stars With Neutrino Cooling

TL;DR

This study investigates how different microphysical nuclear equations of state influence neutron star mergers, affecting gravitational waves, ejecta properties, and neutrino production, with implications for kilonova observations and heavy element synthesis.

Contribution

It provides a detailed analysis of the impact of various realistic equations of state, magnetic fields, and neutrino cooling on merger outcomes and observable signatures.

Findings

Soft equations of state produce more neutron-rich ejecta.

Magnetic fields have subtle effects on post-merger dynamics.

Ejecta composition aligns with kilonova observations.

Abstract

We study the merger of binary neutron stars using different realistic, microphysical nuclear equations of state, as well as incorporating magnetic field and neutrino cooling effects. In particular, we concentrate on the influence of the equation of state on the gravitational wave signature and also on its role, in combination with cooling and electromagnetic effects, in determining the properties of the hypermassive neutron star resulting from the merger, the production of neutrinos, and the characteristics of ejecta from the system. The ejecta we find are consistent with other recent studies that find soft equations of state produce more ejecta than stiffer equations of state. Moreover, the degree of neutron richness increases for softer equations of state. In light of reported kilonova observations (associated to GRB~130603B and GRB~060614) and the discovery of relatively low abundances of heavy, radioactive elements in deep sea deposits (with respect to possible production via supernovae), we speculate that a soft EoS might be preferred---because of its significant production of sufficiently neutron rich ejecta---if such events are driven by binary neutron star mergers. We also find that realistic magnetic field strengths, obtained with a sub-grid model tuned to capture magnetic amplification via the Kelvin-Helmholtz instability at merger, are generally too weak to affect the gravitational wave signature post-merger within a time scale of $\approx 10$~ms but can have subtle effects on the post-merger dynamics.