  We have found correlations between properties of the equation of state for
stellar matter with a phase transition at supernuclear densities and two
characteristic features of a "phase diagram" for rotating compact stars in the
angular velocity - baryon number plane: 1) the critical dividing line between
mono- and two-phase star configurations and 2) the maximum mass line. The
second line corresponds to the minimum mass function for black hole candidates
whereas the first one is observable by a population statistics, e.g. for
Z-sources in low-mass X-ray binaries. The observation of a population gap in
the mass distribution for the latter is suggested as an astrophysical
verification of the existence of a first order phase transition in QCD at high
densities such as the deconfinement.
