Probing Quarkyonic Matter in Neutron Stars with the Bayesian Nuclear-Physics Multi-Messenger Astrophysics Framework

TL;DR

This study uses a Bayesian multi-messenger astrophysics framework to investigate quarkyonic matter in neutron stars, finding significant quark content and specific radius estimates consistent with astrophysical observations.

Contribution

It introduces a novel application of the NMMA framework to constrain quarkyonic matter models using neutron star data, highlighting the potential for quark cores in massive neutron stars.

Findings

Up to 5.9% of neutron star mass can be quarks.

Predicted radius of a 1.4 solar mass neutron star is approximately 13.4 km.

Significant quark content exists in neutron star cores.

Abstract

The interior of neutron stars contains matter at the highest densities realized in our Universe. Interestingly, theoretical studies of dense matter, in combination with the existence of two solar mass neutron stars, indicate that the speed of sound $c_s$ has to increase to values well above the conformal limit ($c_s^2\sim 1/3$) before decreasing again at higher densities. The decrease could be explained by either a strong first-order phase transition or a cross-over transition from hadronic to quark matter. The latter scenario leads to a pronounced peak in the speed of sound reaching values above the conformal limit, naturally explaining the inferred behavior. In this work, we use the Nuclear-Physics Multi-Messenger Astrophysics framework \textsc{NMMA} to compare predictions of the quarkyonic matter model with astrophysical observations of neutron stars, with the goal of constraining model parameters. Assuming quarkyonic matter to be realized within neutron stars, we find that there can be a significant amount of quarks inside the core of neutron stars with masses in the two solar mass range, amounting to up to $\sim 0.13M_\odot$, contributing $\sim 5.9\%$ of the total mass. Furthermore, for the quarkyonic matter model investigated here, the radius of a $1.4M_\odot$ neutron star would be $13.44^{+1.69}_{-1.54} (13.54^{+1.02}_{-1.04})$ km, at $95\%$ credibility, without (with) the inclusion of AT2017gfo.