Constraints on high density equation of state from maximum neutron star mass

TL;DR

This paper investigates how observations of neutron star maximum masses and gravitational wave data can constrain the high-density nuclear matter equation of state, revealing that maximum mass measurements are crucial for understanding matter at several times nuclear saturation density.

Contribution

It introduces a meta-modelling approach to generate diverse equations of state and demonstrates how gravitational wave data and maximum mass measurements can constrain high-density nuclear matter properties.

Findings

Nuclear matter properties below 2n0 do not distinguish different EOS.

Constraints from GW170817's tidal deformability are crucial.

Maximum mass measurements significantly impact high-density EOS constraints.

Abstract

The low density nuclear matter equation of state is strongly constrained by nuclear properties, however, for constraining the high density equation of state it is necessary to resort to indirect information obtained from the observation of neutron stars, compact objects that may have a central density several times nuclear matter saturation density, $n_0$. Taking a meta-modelling approach to generate a huge set of equation of state that satisfy nuclear matter properties close to $n_0$ and that do not contain a first order phase transition, the possibility of constraining the high density equation of state was investigated. The entire information obtained from the GW170817 event for the probability distribution of $\tilde{\Lambda}$ was used to make a probabilistic inference of the EOS, which goes beyond the constraints imposed by nuclear matter properties. Nuclear matter properties close to saturation, below $2n_0$, do not allow us to distinguish between equations of state that predict different neutron star (NS) maximum masses. This is, however, not true if the equation of state is constrained at low densities by the tidal deformability of the NS merger associated to GW170817. Above $3n_0$, differences may be large, for both approaches, and, in particular, the pressure and speed of sound of the sets studied do not overlap, showing that the knowledge of the NS maximum mass may give important information on the high density EOS. Narrowing the maximum mass uncertainty interval will have a sizeable effect on constraining the high density EOS.