Hybrid stars with large strange quark cores constrained by GW170817

Abstract

We analyze the impact of several multi-quark interaction channels on the properties of hybrid stars. Four and eight vector interactions were included in the $SU(3)$ NJL model to describe the quark matter, and all vector like interactions were investigated. The hybrid stars were built starting from an hadronic EoS that satisfy presently accepted nuclear matter properties and considering the quark model constrained by the vacuum properties of several light mesons. The interplay between the 8-quark vector interaction and the 4-quark isovector-vector interaction determine the size of the quark core and its strangeness content. The inclusion of a isovector-vector interaction is essential to obtain large $s$-quark contents and a smaller central speed of sound, although this interaction pushes the onset of quarks to larger densities. It is observed that low mass stars, with a mass below 1.4$M_\odot$ may contain a quark core but with small strangeness content. It is shown that the presently existing mass and tidal deformability constraints from NS observations allow for the existence of hybrid stars with a large strangeness content and large quark cores for binary mass ratios $q=M_2/M_1\gtrsim 0.85$.