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

The stable configurations of non-rotating and rotating hybrid stars composed of colour superconducting quark matter core 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 colour superconducting phase and are computed within the NJL-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 behaviour of the EOSs for the colour superconducting quark matter. However the compositions of hybrid star 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 colour superconducting quark matter. Our results indicate that the EOS for the colour superconducting quark matter can be obtained, by adjusting the parameters of the NJL model, to yield the stable configurations of the hybrid star having the maximum mass $\sim 1.5M_\odot$ in the non-rotating limit and the critical rotation frequency $\sim 1$ kHz.