Hadron-Quark Crossover and Massive Hybrid Stars with Strangeness

TL;DR

This paper proposes that a smooth hadron-quark crossover at relatively low densities with strong interactions can produce massive hybrid neutron stars exceeding 2 solar masses, challenging traditional softening expectations.

Contribution

It introduces a model where a low-density crossover with strong interactions leads to more massive neutron stars with quark cores, contrary to conventional theories.

Findings

Maximum neutron star mass exceeds 2 solar masses.

Crossover at around 3 times nuclear density is crucial.

Results are robust against different hadronic equations of state.

Abstract

Using the idea of a smooth crossover from the hadronic matter with hyperons to quark matter with strangeness, we show that the maximum mass of neutron stars with quark matter core can be larger than those without quark matter core. This is in contrast to the conventional softening of equation of state due to exotic components at high density. Essential conditions to reach our conclusion are (i) the crossover takes place at relatively low densities, around 3 times the normal nuclear density, and (ii) the quark matter is strongly interacting in the crossover region. By these, the pressure of the system can be greater than that of purely hadronic matter in the crossover region and leads to the maximum mass greater than 2 solar mass. This conclusion is insensitive to the different choice of the hadronic equation of state with hyperons. Several implications of this result to the nuclear incompressibility, the hyperon mixing, and the neutrino cooling are also remarked.