Quark deconfinement in neutron stars and astrophysical implications

We investigate the quark deconfinement phase transition in cold (T=0) and hot β-stable hadronic matter. Assuming a first-order phase transition, we calculate and compare the nucleation rate and the nucleation time due to quantum and thermal nucleation mechanisms. We show that above a threshold value of the central pressure a pure hadronic star (HS) (i.e. a compact star with no fraction of deconfined quark matter (QM)) is metastable to the conversion to a quark star (QS) (i.e. a hybrid star or a strange star). This process liberates a huge amount of energy, of the order of 1053 erg, which produces a powerful neutrino burst, likely accompanied by intense gravitational waves emission, and possibly by a second delayed (with respect to the supernova explosion forming the HS) explosion which could be the energy source of a powerful gamma-ray burst (GRB). This stellar conversion process populates the QS branch of compact stars, thus one has in the universe two coexisting families of compact stars: HSs and QSs. We introduce the concept of critical mass Mcr for cold HSs and proto-hadronic stars (PHSs), and the concept of limiting conversion temperature for PHSs. We show that PHSs with a mass M<Mcr could survive the early stages of their evolution without decaying to QSs. Finally, we discuss the possible evolutionary paths of PHSs.