Tidal Deformabilities and Radii of Neutron Stars from the Observation of GW170817

TL;DR

This paper uses gravitational-wave data from GW170817 to measure neutron star tidal deformabilities and radii, providing the first such constraints from gravitational waves with physical equation of state implications.

Contribution

It introduces a Bayesian analysis method that incorporates electromagnetic observations and assumptions about the equation of state to constrain neutron star properties from gravitational waves.

Findings

Tidal deformability rom GW170817 is ound to be inite with credible intervals.

Neutron star radii are constrained to all between 8.9 and 13.2 km.

First gravitational-wave-based lower bounds on neutron star deformability and radii.

Abstract

We use gravitational-wave observations of the binary neutron star merger GW170817 to explore the tidal deformabilities and radii of neutron stars. We perform Bayesian parameter estimation with the source location and distance informed by electromagnetic observations. We also assume that the two stars have the same equation of state; we demonstrate that for stars with masses comparable to the component masses of GW170817, this is effectively implemented by assuming that the stars' dimensionless tidal deformabilities are determined by the binary's mass ratio $q$ by $\Lambda_1/\Lambda_2 = q^6$. We investigate different choices of prior on the component masses of the neutron stars. We find that the tidal deformability and 90$\%$ credible interval is $\tilde{\Lambda}=222^{+420}_{-138}$ for a uniform component mass prior, $\tilde{\Lambda}=245^{+453}_{-151}$ for a component mass prior informed by radio observations of Galactic double neutron stars, and $\tilde{\Lambda}=233^{+448}_{-144}$ for a component mass prior informed by radio pulsars. We find a robust measurement of the common areal radius of the neutron stars across all mass priors of $8.9 \le \hat{R} \le 13.2$ km, with a mean value of $\langle \hat{R} \rangle = 10.8$ km. Our results are the first measurement of tidal deformability with a physical constraint on the star's equation of state and place the first lower bounds on the deformability and areal radii of neutron stars using gravitational waves.