Nuclear and Hybrid Equations of State in Light of the Low-Mass Compact Star in HESS J1731-347

TL;DR

This study evaluates over 500 nuclear equations of state against recent low-mass compact star measurements, revealing challenges in reconciling nuclear models with astrophysical data and suggesting hybrid models with quark cores are promising.

Contribution

It systematically tests a large set of nuclear models against new stellar constraints and highlights the potential of hybrid quark matter models to satisfy these constraints.

Findings

None of the nuclear models meet all constraints at 68% credibility.

Hybrid equations of state with quark cores can meet the constraints.

There is a tension between nuclear theory and astrophysical observations.

Abstract

We sample over $500$ relativistic mean-field theories constrained by chiral effective field theory and properties of isospin-symmetric nuclear matter and test them against known stellar structure constraints. This includes a recent mass and radius measurement of a compact object in supernova remnant HESS J1731-347, with an unusually low mass of $M=0.77^{+0.20}_{-0.17}\,M_{\odot}$ and a compact radius of $R=10.4^{+0.86}_{-0.78}$ km. We show that none of the sampled nuclear models meet all constraints at the $68\,\%$ credibility level, but that hybrid equations of state with a quark matter inner core and nuclear outer core easily can. This indicates a tension between astrophysical constraints and low-energy nuclear theory.