Properties of quark matter and hybrid stars from a quasiparticle model

We investigate the global properties of hybrid stars and quark-matter cores by using a quasiparticle model that rules out the possibility of the existence of absolutely stable strange quark matter within the hybrid stars. Results from our study indicate that the coupling constant g can stiffen the equation of state of hybrid star matter and thus increase the hybrid star maximum mass and its tidal deformability, whereas it also decreases the mass and radius of the pure quark. By breaking the absolutely stable condition, we provide the maximum mass, minimum radius R-1.4, and minimum tidal deformation Lambda(1.4) of the hybrid stars as well as the maximum mass and radius of the quark-matter core with different g values within the allowable regions (the energy per nucleon of both u-d quark matter and strange quark matter must exceed 930 MeV) on the g-B-1/4 plane. In addition, we find that a step change of the sound velocity occurs in the hadron-quark mixed phase, and the approximate rule that the polytropic index gamma <= 1.75 can also be used as a criterion for separating hadronic from quark matter in our work. Our results also confirm that the sizable quark-matter cores (R-QC > 6.5 km) containing the mixed phase can appear in 2M(circle dot) massive stars.