Composition and stability of hybrid stars with hyperons and quark color-superconductivity

TL;DR

This paper explores whether hyperons and quark matter can exist in massive neutron stars by modeling their equation of state, showing that stable stars with hyperons and color-superconducting quark matter are possible if certain conditions are met.

Contribution

It introduces a combined equation of state using hyper-nuclear density functional and the Nambu-Jona-Lasinio model to explain massive stars with hyperons and quark matter.

Findings

Stable stars with mass ≥ 1.97 solar masses can contain hyperons and quark matter.

A stiff nuclear matter equation of state is necessary above saturation density.

Quark matter transition occurs at a few times nuclear saturation density.

Abstract

The recent measurement of a $1.97\pm 0.04$ solar-mass pulsar places a stringent lower bound on the maximum mass of compact stars and therefore challenges the existence of any agents that soften the equation of state of ultra-dense matter. We investigate whether hyperons and/or quark matter can be accommodated in massive compact stars by constructing an equation of state based on a combination of phenomenological relativistic hyper-nuclear density functional and an effective model of quantum chromodynamics (the Nambu-Jona-Lasinio model). Stable configurations are obtained with $M \ge 1.97 M_{\sun}$ featuring hyper-nuclear and quark matter in color superconducting state if the equation of state of nuclear matter is stiff above the saturation density, the transition to quark matter takes place at a few times the nuclear saturation density, and the repulsive vector interactions in quark matter are substantial.