Hadron-Quark Crossover and Massive Hybrid Stars

TL;DR

This paper proposes a new equation of state for neutron stars based on a hadron-quark crossover, showing that massive hybrid stars exceeding 2 solar masses are possible if the crossover occurs at high density and quark matter is strongly interacting.

Contribution

It introduces a novel EOS model based on a smooth hadron-quark crossover, challenging the traditional first-order transition approach and demonstrating conditions for massive neutron stars.

Findings

Maximum neutron star mass can exceed 2 solar masses.

Crossover at around three times nuclear density is crucial.

Strongly interacting quark matter leads to stiffer EOS.

Abstract

On the basis of the percolation picture from the hadronic phase with hyperons to the quark phase with strangeness, we construct a new equation of state (EOS) with the pressure interpolated as a function of the baryon density. The maximum mass of neutron stars can exceed $2M_{\odot}$ if the following two conditions are satisfied; (i) the crossover from the hadronic matter to the quark matter takes place at around three times the normal nuclear matter density, and (ii) the quark matter is strongly interacting in the crossover region and has stiff equation of state. This is in contrast to the conventional approach assuming the first order phase transition in which the EOS becomes always soft due to the presence of the quark matter at high density. Although the choice of the hadronic EOS does not affect the above conclusion on the maximum mass, the three-body force among nucleons and hyperons plays an essential role for the onset of the hyperon mixing and the cooling of neutron stars.