From Quark Stars to Hybrid Stars

We show the possible existence of compact stars having a surface composed of a mixed phase of quarks and hadrons. This scenario can be realized both for self-bound stars, satisfying the so-called Witten-Bodmer hypothesis, and for gravitationally bound stars. This class of solutions of the Tolman-Oppenheimer-Volkoff equation can be obtained in all the models we discuss, within a physically acceptable range of values of the model parameters.