# Constraints on the Neutron Star Equation of State from GW170817

## TL;DR

The paper reviews how the gravitational wave event GW170817 has been used to constrain the neutron star equation of state, revealing insights into neutron star radii, maximum mass, and the importance of disentangling thermal effects.

## Contribution

It provides a comprehensive review of constraints on the neutron star EOS from GW170817 and introduces new radius estimates based on the effective tidal deformability relationship.

## Key findings

- Neutron star radius from GW170817 is between 9.8 and 13.2 km.
- Maximum neutron star mass constrained to be less than 2.3 solar masses.
- Bayesian inference methods have been used to directly constrain the EOS.

## Abstract

The first detection of gravitational waves from a neutron star-neutron star merger, GW170817, has opened up a new avenue for constraining the ultradense-matter equation of state (EOS). The deviation of the observed waveform from a point-particle waveform is a sensitive probe of the EOS controlling the merging neutron stars' structure. In this topical review, I discuss the various constraints that have been made on the EOS in the year following the discovery of GW170817. In particular, I review the surprising relationship that has emerged between the effective tidal deformability of the binary system and the neutron star radius. I also report new results that make use of this relationship, finding that the radius inferred from GW170817 lies between 9.8 and 13.2 km at 90% confidence, with distinct likelihood peaks at 10.8 and 12.3 km. I compare these radii, as well as those inferred in the literature, to X-ray measurements of the neutron star radius. I also summarize the various maximum mass constraints, which point towards a maximum mass < 2.3 M_sun, depending on the fate of the remnant, and which can be used to additionally constrain the high-density EOS. I review the constraints on the EOS that have been performed directly, through Bayesian inference schemes. Finally, I comment on the importance of disentangling thermal effects in future EOS constraints from neutron star mergers.