Astrophysical Implications of Neutron Star Inspiral and Coalescence

TL;DR

This paper reviews how gravitational wave and electromagnetic observations of neutron star mergers have advanced understanding of neutron star properties, element formation, and gamma-ray bursts.

Contribution

It synthesizes recent observational results and theoretical insights to constrain neutron star equations of state and related astrophysical phenomena.

Findings

Neutron star mergers provide key insights into the origin of heavy elements.

Observations constrain neutron star radii and maximum mass.

Post-merger oscillations offer future constraints on neutron star physics.

Abstract

The first inspiral of two neutron stars observed in gravitational waves was remarkably close, allowing the kind of simultaneous gravitational wave and electromagnetic observation that had not been expected for several years. Their merger, followed by a gamma-ray burst and a kilonova, was observed across the spectral bands of electromagnetic telescopes. These GW and electromagnetic observations have led to dramatic advances in understanding short gamma-ray bursts; determining the origin of the heaviest elements; and determining the maximum mass of neutron stars. From the imprint of tides on the gravitational waveforms and from observations of X-ray binaries, one can extract the radius and deformability of inspiraling neutron stars. Together, the radius, maximum mass, and causality constrain the neutron-star equation of state, and future constraints can come from observations of post-merger oscillations. We selectively review these results, filling in some of the physics with derivations and estimates.