A critical examination of constraints on the equation of state of dense matter obtained from GW170817

TL;DR

This paper critically examines constraints on the dense matter equation of state derived from GW170817, using models constrained by nuclear physics and exploring implications of phase transitions on neutron star properties.

Contribution

It introduces a comparison between a minimal smooth EOS model and a more general model allowing phase transitions, analyzing their impact on tidal polarizability predictions.

Findings

GW170817 does not significantly improve EOS constraints when models are limited to nuclear saturation density.

Predicted combined tidal polarizability range is narrower than LIGO-Virgo estimates.

Neutron star radius for 1.4 solar masses is constrained between 9.0 and 13.6 km.

Abstract

The correlation of the tidal polarizabilities $\Lambda_1$-$\Lambda_2$ for GW170817 is predicted by combining dense-matter equations of state (EOSs) that satisfy nuclear physics constraints with the chirp mass and mass asymmetry for this event. Our models are constrained by calculations of the neutron-matter EOS using chiral effective field theory Hamiltonians with reliable error estimates up to once or twice the nuclear saturation density. In the latter case, we find that GW170817 does not improve our understanding of the EOS. We contrast two distinct extrapolations to higher density: a minimal model (MM) which assumes that the EOS is a smooth function of density described by a Taylor expansion and a more general model parametrized by the speed of sound that admits phase transitions. This allows us to identify regions in the $\Lambda_1$-$\Lambda_2$ plots that could favor the existence of new phases of matter in neutron stars. We predict the combined tidal polarizability of the two neutron stars in GW170817 to be $80\le \tilde{\Lambda}\le 580$ ($280\le \tilde{\Lambda}\le 480$ for the MM), which is smaller than the range suggested by the LIGO-Virgo data analysis. Our analysis also shows that GW170817 requires a NS with $M=1.4M_\odot$ to have a radius $9.0<R_{1.4}<13.6$~km ($ 11.3 <R_{1.4}< 13.6$~km for the MM).