EQUILIBRIUM-CONFIGURATIONS FOR QUARK-DIQUARK STARS AND THE PROBLEM OFHER X-1 MASS

We report new calculations of the physical properties of a quark-diqua rk plasma. A vacuum contribution is taken into account and is responsi ble for the appearance of a stable state at zero pressure and at a bar yon density of about 2.2 times the nuclear matter density in this mode l. The resulting equation of state was used to integrate numerically t he Tolman-Oppenheimer-Volkoff equations. The mass-radius relationship has been derived from a series of equilibrium configurations constitut ed by a mixture of quarks and diquarks. These stellar models, which ar e representative of a whole class, may be helpful to understand the po ssible compactness of the X-ray source Her X-l and related objects.