Thermal behavior as indicator for hyperons in binary neutron star merger remnants

TL;DR

This study investigates how hyperons affect the thermal behavior and gravitational-wave signals of neutron star merger remnants, providing a potential observational signature for hyperonic matter in high-density astrophysical objects.

Contribution

It offers the first comprehensive analysis of hyperons in neutron star mergers, linking thermal effects to measurable gravitational-wave frequency shifts, and proposes a new observational method to detect hyperons.

Findings

Hyperons increase postmerger gravitational-wave frequency by up to 150 Hz.

Finite temperature enhances hyperon production, reducing pressure in merger remnants.

The gravitational-wave frequency shift due to hyperons is potentially measurable.

Abstract

We provide the first comprehensive study of hyperons in neutron star mergers and quantify their specific impact. We discuss the thermal behavior of hyperonic equations of state~(EoSs) as a distinguishing feature from purely nucleonic models in the remnants of binary mergers using a large set of numerical simulations. Finite temperature enhances the production of hyperons, which leads to a reduced pressure as highly degenerate nucleons are depopulated. This results in a characteristic increase of the dominant postmerger gravitational-wave frequency by up to $\sim150$~Hz compared to purely nucleonic EoS models. By our comparative approach we can directly link this effect to the occurrence of hyperons. Although this feature is generally weak, it is in principle measurable if the EoS and stellar parameters of cold neutron stars are sufficiently well determined. Considering that the mass-radius relations of purely nucleonic and hyperonic EoSs may be indistinguishable and the overall challenge to infer the presence of hyperons in neutron stars, these findings are important as a new route to answer the outstanding question about hyperonic degrees of freedom in high-density matter.