Thermal evolution of hybrid stars within the framework of a nonlocal Nambu--Jona-Lasinio model

TL;DR

This paper investigates the thermal evolution of neutron stars with quark matter cores using a nonlocal Nambu-Jona-Lasinio model, revealing that high-mass stars may contain significant deconfined quark matter and match observed cooling data.

Contribution

It introduces a nonlocal extension of the NJL model with vector interactions to study quark-hybrid stars' thermal evolution, providing new insights into their composition and cooling behavior.

Findings

High-mass neutron stars may contain 35-40% deconfined quark matter.

Canonical 1.4 M_sun neutron stars likely lack deconfined quark matter.

Model matches observed cooling of Cas A with strong proton pairing.

Abstract

We study the thermal evolution of neutron stars containing deconfined quark matter in their core. Such objects are generally referred to as quark-hybrid stars. The confined hadronic matter in their core is described in the framework of non-linear relativistic nuclear field theory. For the quark phase we use a non-local extension of the SU(3) Nambu Jona-Lasinio model with vector interactions. The Gibbs condition is used to model phase equilibrium between confined hadronic matter and deconfined quark matter. Our study indicates that high-mass neutron stars may contain between 35 and 40 % deconfined quark-hybrid matter in their cores. Neutron stars with canonical masses of around $1.4\, M_\odot$ would not contain deconfined quark matter. The central proton fractions of the stars are found to be high, enabling them to cool rapidly. Very good agreement with the temperature evolution established for the neutron star in Cassiopeia A (Cas A) is obtained for one of our models (based on the popular NL3 nuclear parametrization), if the protons in the core of our stellar models are strongly paired, the repulsion among the quarks is mildly repulsive, and the mass of Cas A has a canonical value of $1.4\, M_\odot$.