Compact stars with color superconducting quark matter

We study compact stars that contain quark matter. We look at the effect of color superconductivity in the quark matter on the nuclear-quark matter transition density, mass-radius relationship, and the density discontinuity at the boundary between nuclear and quark matter. We find that color superconducting quark matter will occur in compact stars at values of the bag constant where ordinary quark matter would not be allowed. We are able to construct ``hybrid'' stars with a color superconducting quark matter interior and nuclear matter surface, with masses in the range $1.3--{1.6M}_{\ensuremath{\bigodot}}$ and radii 8--11 km. Our results are consistent with recent mass-radius limits based on absorption lines from EXO0748-676.