Hybrid Stars in the Framework of different NJL Models

TL;DR

This paper models the equation of state for hybrid stars using various NJL models, analyzing how different phase transition constructions affect the stability and structure of high-mass neutron stars with quark cores.

Contribution

It compares local and non-local NJL models with different phase transition methods to understand their impact on hybrid star properties.

Findings

Hybrid stars with quark cores can reach up to 2.4 solar masses.

Gibbs construction allows stable mixed phases in high-mass stars.

Maxwell construction often destabilizes stars or results in short hybrid branches.

Abstract

We compute models for the equation of state (EoS) of the matter in the cores of hybrid stars. Hadronic matter is treated in the non-linear relativistic mean-field approximation, and quark matter is modeled by three-flavor local and non-local Nambu$-$Jona-Lasinio (NJL) models with repulsive vector interactions. The transition from hadronic to quark matter is constructed by considering either a soft phase transition (Gibbs construction) or a sharp phase transition (Maxwell construction). We find that high-mass neutron stars with masses up to $2.1-2.4 M_\odot$ may contain a mixed phase with hadrons and quarks in their cores, if global charge conservation is imposed via the Gibbs conditions. However, if the Maxwell conditions is considered, the appearance of a pure quark matter core either destabilizes the star immediately (commonly for non-local NJL models) or leads to a very short hybrid star branch in the mass-radius relation (generally for local NJL models).