Discriminating Strange Star Mergers from Neutron Star Mergers by Gravitational-Wave Measurements

TL;DR

This study uses relativistic hydrodynamical simulations to identify gravitational-wave features that can distinguish strange star mergers from neutron star mergers, potentially confirming the strange matter hypothesis.

Contribution

It demonstrates that gravitational-wave signals have distinct signatures for strange star mergers, providing a new method to test the existence of strange quark matter in compact stars.

Findings

Strange star mergers produce higher characteristic frequencies in GW signals.

Distinct remnant structures differentiate SS mergers from NS mergers.

Thermal effects significantly influence merger dynamics and GW signatures.

Abstract

We perform three-dimensional relativistic hydrodynamical simulations of the coalescence of strange stars (SSs) and explore the possibility to decide on the strange matter hypothesis by means of gravitational-wave (GW) measurements. Selfbinding of strange quark matter (SQM) and the generally more compact stars yield features that clearly distinguish SS from neutron star (NS) mergers, e.g. hampering tidal disruption during the plunge of quark stars. Furthermore, instead of forming dilute halos around the remnant as in the case of NS mergers, the coalescence of SSs results in a differentially rotating hypermassive object with a sharp surface layer surrounded by a geometrically thin, clumpy high-density SQM disk. We also investigate the importance of including non-zero temperature equations of state (EoSs) in NS and SS merger simulations. In both cases we find a crucial sensitivity of the dynamics and outcome of the coalescence to thermal effects, which, e.g., determine the outer remnant structure and the delay time of the dense remnant core to black hole collapse. For comparing and classifying the GW signals, we use a number of characteristic quantities like the maximum frequency during inspiral or the dominant frequency of oscillations of the postmerger remnant. In general, these frequencies are higher for SS mergers. If not, additional features of the GW luminosity spectrum may help to discriminate coalescence events of the different types. Future GW measurements may thus help to decide on the existence of SQM stars. (abridged)