Constraining the dense matter equation of state with joint analysis of NICER and LIGO/Virgo measurements

TL;DR

This paper combines X-ray and gravitational wave data to better constrain the dense matter equation of state, incorporating recent measurements and exploring different merger scenarios to improve understanding of neutron star properties.

Contribution

It extends previous EOS constraints by integrating NICER and LIGO/Virgo data, including the possibility of neutron star-black hole mergers, providing a more comprehensive analysis.

Findings

Increased constraints on the EOS from combined data

Inclusion of the 2.14 solar mass pulsar measurement improves constraints

Neutron star-black hole merger scenario yields weaker EOS constraints

Abstract

The NICER collaboration recently published a joint estimate of the mass and the radius of PSR J0030+0451, derived via X-ray pulse-profile modeling. Raaijmakers et al. (2019) explored the implications of this measurement for the dense matter equation of state (EOS) using two parameterizations of the high-density EOS: a piecewise-polytropic model, and a model based on the speed of sound in neutron stars. In this work we obtain further constraints on the EOS following this approach, but we also include information about the tidal deformability of neutron stars from the gravitational wave signal of the compact binary merger GW170817. We compare the constraints on the EOS to those set by the recent measurement of a 2.14 solar mass pulsar, included as a likelihood function approximated by a Gaussian, and find a small increase in information gain. To show the flexibility of our method, we also explore the possibility that GW170817 was a neutron star-black hole merger, which yields weaker constraints on the EOS.