Stable configurations of hybrid stars with color-flavor-locked core

Abstract

We construct static and mass-shedding limit sequences of hybrid stars, composed of a color flavour locked (CFL) quark matter core, for a set of equations of state (EOSs). The EOS for the hadronic matter is obtained using an appropriately calibrated, extended field theoretical based, relativistic mean-field model. The MIT bag model is employed to compute the EOSs of the CFL quark matter for different values of the CFL gap parameter in the range of 50–150 MeV with the deconfinement phase transition density ranging from $4{\rho }_0$ to $6{\rho }_0$ (${\rho }_0=0.16{\mathrm{fm}}^{-3}$). We find that, depending on the values of the CFL gap parameter and the deconfinement phase transition density, the sequences of stable configurations of hybrid stars either form third families of the compact stars or bifurcate from the hadronic sequence. The hybrid stars have masses $1.0–2.1M_{\odot }$ with radii 9–13.5 km. The maximum values of the mass-shedding limit frequency for such hybrid stars are 1–2 kHz. For the smaller values of the CFL gap parameter and the deconfinement phase transition density, mass-radius relationships are in harmony with those deduced by applying an improved hydrogen atmosphere model to fit the high quality spectra from compact star X7 in the globular cluster 47 Tucanae. We observed, for some cases, that the third family of compact stars exist in the static sequence but disappear from the mass-shedding limit sequence. Our investigation suggests that the third family of compact stars in the mass-shedding limit sequence is more likely to appear, provided these stars have maximum mass in the static limit higher than their second-family counterpart composed of pure hadronic matter.