Maximum mass of compact stars from gravitational wave events with finite-temperature equations of state

TL;DR

This paper establishes universal relations for hot, fast-rotating compact stars and uses gravitational wave data to set new upper limits on the maximum mass of cold neutron stars, considering finite-temperature effects.

Contribution

It introduces universal relations between global parameters of hot, rotating compact stars and applies them to GW170817 to refine maximum mass constraints.

Findings

Upper limit on static neutron star mass: 2.15-2.24 solar masses.

Finite temperature effects relax previous mass constraints.

Universal relations connect hot and cold star configurations.

Abstract

We conjecture and verify a set of universal relations between global parameters of hot and fast-rotating compact stars, including a relation connecting the masses of the mass-shedding (Kepler) and static configurations. We apply these relations to the GW170817 event by adopting the scenario in which a hypermassive compact star remnant formed in a merger evolves into a supramassive compact star that collapses into a black hole once the stability line for such stars is crossed. We deduce an upper limit on the maximum mass of static, cold neutron stars $ 2.15^{+0.10}_{-0.07}\le M^\star_{\mathrm{TOV}} \le 2.24^{+0.12}_{-0.10} $ for the typical range of entropy per baryon $2 \le S/A \le 3$ and electron fraction $Y_e = 0.1$ characterizing the hot hypermassive star. Our result implies that accounting for the finite temperature of the merger remnant relaxes previously derived constraints on the value of the maximum mass of a cold, static compact star.