Investigating the mass-ratio dependence of the prompt-collapse threshold with numerical-relativity simulations

TL;DR

This study uses relativistic simulations to explore how the mass ratio of binary neutron stars influences the threshold for prompt black hole formation, impacting merger dynamics and observable signals.

Contribution

It provides new empirical relations and models for the effect of mass ratio and equation of state on the prompt-collapse threshold and remnant properties.

Findings

Mass ratio significantly affects the prompt-collapse threshold.

Empirical relation for threshold mass based on collapse-time.

Modeling of tidal parameters influenced by mass ratio and EOS.

Abstract

The next observing runs of advanced gravitational-wave detectors will lead to a variety of binary neutron star detections and numerous possibilities for multi-messenger observations of binary neutron star systems. In this context a clear understanding of the merger process and the possibility of prompt black hole formation after merger is important, as the amount of ejected material strongly depends on the merger dynamics. These dynamics are primarily affected by the total mass of the binary, however, the mass ratio also influences the postmerger evolution. To determine the effect of the mass ratio, we investigate the parameter space around the prompt-collapse threshold with a new set of fully relativistic simulations. The simulations cover three equations of state and seven mass ratios in the range of $1.0 \leq q \leq 1.75$, with five to seven simulations of binary systems of different total mass in each case. The threshold mass is determined through an empirical relation based on the collapse-time, which allows us to investigate effects of the mass-ratio on the threshold mass and also on the properties of the remnant system. Furthermore, we model effects of mass ratio and equation of state on tidal parameters of threshold configurations.