Phase Transitions In Compact Stars
  We report on a three--month research project for undergraduate students about the mass-radius relation of compact stars. The equation of state used is constrained at low densities by well-established equations of state of the nuclear phase (the solid crust) and then extended to higher densities with a phenomenological, parametric approach. A first order phase transition from hadronic matter to a phase of higher density, assumed to be quark matter is studied in addition. The mass-radius relation is obtained by solving numerically the Tolman-Oppenheimer-Volkoff equation. We derive some conditions for the existence of a third family of compact stars on the form of the equation of state and its different global properties. 
Jean Macher and Jurgen Schaffner-Bielich