Quark deconfinement in compact stars and astrophysical implications

We explore some of the astrophysical consequences of the hadron-quark phase transition in compact stars. In particular, we describe a new model which is able to explain how a gamma-ray burst (GRB) can take place days or years after a supernova explosion. We show that above a threshold value of the gravitational mass a pure hadronic star ("neutron star") is metastable to the conversion into a quark star (hybrid star or strange star), i.e. a star made at least in part of deconfined quark matter. The stellar conversion process can be delayed if finite size effects at the interface between hadronic and deconfined quark matter phases are taken into account. A huge amount of energy, on the order of 10(52) - 10(53) ergs, is released during the conversion process and can produce a powerful gamma-ray burst. The delay between the supernova explosion generating the metastable neutron star and the Dew collapse can explain the delay inferred in GRB 990705 and in GRB 011211. Next, we explore the consequences of the metastability of "massive" neutron stars and of the existence of stable compact quark stars on the concept of limiting mass of compact stars