Signatures of quark matter from neutron star mass-radius curve

Abstract

Signatures of the presence of quark matter inside neutron stars are obtained from the analysis of more than 250,000 mass-radius curves that describe nucleonic, hyperonic and hybrid stars, based on five different hadronic relativistic mean-field models and four different descriptions of quark matter. A radius maximum occurring above $1.7\,M_\odot$ strongly favors quark matter inside the star. A second criterion identifying the presence of quark matter is $X>-0.2$km, where X=[R(2.0)-R(1.6)]-[R(1.6)-R(1.4)] is obtained from the radius of stars with 2.0, 1.6 and 1.4 $M_\odot$. It is also shown that most of the hyperonic stars have a radius maximum that peaks around 1.5$M_\odot$ and compactness below 0.27 for the maximum-mass configuration, while for the nucleonic stars that have a radius maximum, this peaks below 1.3$M_\odot$ and the compactness of the maximum-mass configuration lies above 0.26.