Probing Extreme-Density Matter with Gravitational Wave Observations of Binary Neutron Star Merger Remnants

TL;DR

This study explores how gravitational wave signals from neutron star merger remnants can reveal the properties of matter at extreme densities, highlighting the potential for future detections to inform nuclear physics.

Contribution

It demonstrates, through numerical simulations, that postmerger gravitational wave signals encode information about the equation of state at high densities, which can be detected with advanced observatories.

Findings

EOS softening affects GW luminosity and phase

Detectable up to several Mpcs with advanced detectors

Postmerger signals require new modeling strategies

Abstract

We present a proof-of-concept study, based on numerical-relativity simulations, of how gravitational waves (GWs) from neutron star merger remnants can probe the nature of matter at extreme densities. Phase transitions and extra degrees of freedom can emerge at densities beyond those reached during the inspiral, and typically result in a softening of the equation of state (EOS). We show that such physical effects change the qualitative dynamics of the remnant evolution, but they are not identifiable as a signature in the GW frequency, with the exception of possible black-hole formation effects. The EOS softening is, instead, encoded in the GW luminosity and phase and is in principle detectable up to distances of the order of several Mpcs with advanced detectors and up to hundreds of Mpcs with third generation detectors. Probing extreme-density matter will require going beyond the current paradigm and developing a more holistic strategy for modeling and analyzing postmerger GW signals.