Cosmic Separation of Phases: the microsecond universe and the neutron star
It is entirely plausible under reasonable condition, that a first order QCD phase transition occurred from quarks to hadrons when the universe was about a microsecond old. Relics, if there be any, after the quark hadron phase transition are the most deciding signatures of the phase transition. It is shown in this paper that the quark nuggets, possible relics of first order QCD phase transitions with baryon number larger than $10^{43}$ will survive the entire history of the universe uptil now and can be considered as candidates for the cold dark matter. The spin down core of the neutron star on the high density low temperature end of the phase diagramme initiates transition from hadrons to quarks. As the star spins down, the size of the core goes on increasing. Recently discovered massive Pulsar PSRJ 1614-2230 with a mass of 1.97$\pm$0.04 $M_{\odot}$ most likely has a strongly interacting quark core. What possible observables can there be from these neutron stars?