Hadron-Quark Crossover and Hot Neutron Stars at Birth

TL;DR

This paper develops a new finite-temperature equation of state incorporating hadron-quark crossover and analyzes its impact on the structure and evolution of hot neutron stars at birth.

Contribution

It introduces a novel isentropic EOS with hadron-quark crossover and applies it to study hot neutron star properties at birth.

Findings

Hot neutron stars with crossover have lower core temperature and density.

Energy release during contraction to cold neutron stars is about 0.04 solar masses.

Spin-up rate during contraction is approximately 14%.

Abstract

We construct a new isentropic equation of state (EOS) at finite temperature "CRover" on the basis of the hadron-quark crossover at high density. By using the new EOS, we study the structure of hot neutron stars at birth with the typical lepton fraction ($Y_l=0.3-0.4$) and the typical entropy per baryon ($S=1-2$). Due to the gradual appearance of quark degrees of freedom at high density, the temperature T and the baryon density at the center of the hot neutron stars with the hadron-quark crossover are found to be smaller than those without the crossover by a factor of 2 or more. Typical energy release due to the contraction of a hot neutron star to a cold neutron star with 1.4 solarmass is shown to be about 0.04 solarmass with the spin-up rate about 14%.