Dense Quark Matter in Compact Stars

According to quantum chromodynamics (QCD), matter at ultra-high densities will take the form of a color-superconducting quark liquid, in which there is a condensate of Cooper pairs of quarks near the Fermi surface. I present a review of the physics of color superconductivity, and discuss possible signatures by which it might be detected in compact stars. I give a detailed discussion of the effects of color superconductivity on the mass-radius relationship of compact stars, showing that one would have to fix the bag constant by other measurements in order to see the effects of color superconductivity. An additional parameter in the quark matter equation of state connected with perturbative corrections allows quark matter to imitate nuclear matter over the relevant density range, so that hybrid stars can show a mass-radius relationship very similar to that of nuclear matter, and their masses can reach 1.9 M_⊙.