Effects of nuclear matter properties in neutron star mergers

Abstract

The dynamics in mergers of binary neutron star (BNS) systems depend sensitively on the equation of state (EOS) of dense matter. This has profound implications on the emission of gravitational waves (GWs) and the ejection of matter in the merger and post-merger phases and is thus of high interest for multimessenger astronomy. Today, a variety of nuclear EOSs are available with various underlying microphysical models. This calls for a study to focus on EOS effects from different physical nuclear matter properties and their influence on BNS mergers. We perform simulations of equal-mass BNS mergers with a set of nine different EOSs based on Skyrme density functionals. In the models, we systematically vary the effective nucleon mass, incompressibility, and symmetry energy at saturation density. This allows us to investigate the influence of specific nuclear matter properties on the dynamics of BNS mergers. We analyse the impact of these properties on the merger dynamics, the fate of the remnant, disc formation, ejection of matter, and GW emission. Our results indicate that some aspects of the merger, such as the frequencies of the post-merger GW spectrum and the shock-heated ejecta mass, are sensitive to the EOS around saturation density while others, such as the contraction of the remnant and the tidal ejecta mass, are sensitive to the behaviour towards higher densities, e.g. characterized by the slope of the pressure versus density. The detailed density dependence of the EOS thus needs to be taken into account to describe its influence on BNS mergers.