Equations of state and stability of color-superconducting quark matter cores in hybrid stars

The stable configurations of nonrotating and rotating hybrid stars composed of color-superconducting quark matter cores are constructed using several equations of state (EOSs). We use a set of diverse EOSs for the nuclear matter which represents the low density phase. The EOSs at higher densities correspond to the quark matter in the color-superconducting phase and are computed within the Nambu-Jona-Lasinio-like model for different values of the scalar diquark and vector current couplings strengths. The phase transition to the quark matter is computed by a Maxwell construction. We find that the stability of the hybrid stars are mainly governed by the behavior of the EOSs for the color-superconducting quark matter. However the compositions of hybrid stars are sensitive to the EOS of the nuclear matter. The value of the critical rotation frequency for the hybrid star depends strongly on the EOS of the nuclear matter as well as that for the color-superconducting quark matter. Our results indicate that the EOS for the color-superconducting quark matter can be obtained, by adjusting the parameters of the Nambu-Jona-Lasinio model, to yield the stable configurations of the hybrid star having the maximum mass ∼1.5M· in the nonrotating limit and the critical rotation frequency ∼1 kHz.