Finding quark content of neutron stars in light of GW170817

TL;DR

This paper explores the presence of quark matter inside neutron stars using gravitational wave data from GW170817, showing phase transitions can reconcile models with observations and constrain neutron star radii.

Contribution

It demonstrates that nucleonic equations of state can be compatible with gravitational wave constraints when including quark phase transitions, and provides bounds on neutron star radii.

Findings

Nucleonic EOSs become consistent with GW data when phase transition to quark matter is included.

Some neutron stars may have small quark cores with mass up to 0.17 solar masses.

Upper limit on neutron star radius of 12.9 km for a 1.4 solar mass star.

Abstract

The detection of gravitational waves from GW170817 has provided a new opportunity to constrain the equation of state (EOS) of neutron stars. In this article, we investigate the possible existence of quarks inside the neutron star core in the context of GW170817. The nucleon phase is treated within the relativistic nuclear mean-field approach where we have employed a fully comprehensive set of available models, and the quark phase is described in the Bag model. We show that the nucleonic EOSs which are inconsistent with the tidal deformability bound become consistent when phase transition to quark matter via Gibbs construction is allowed. We find that several nucleonic EOSs support the presence of pure quark matter core with a small mass not more than $0.17M_\odot$ confined within a radius of 0.9 km. We also find that the strong correlation between tidal deformability and neutron star radii observed for pure nucleonic stars does persist even with a nucleon-quark phase transition and provides an upper limit on the radius of $R_{1.4} \lesssim 12.9$ km for a $1.4M_\odot$ neutron star.