PROMPT SUBSIDENCE OF A PROTO-NEUTRON STAR INTO A BLACK-HOLE

A newly formed proto-neutron star, prior to the loss of neutrinos, will consist of a charge-neutral mixture of neutrons, protons, electrons, muons, and trapped neutrinos in the lowest energy state available under these circumstances. However, in a few seconds, the neutrino will escape, enabling the interior of the star to find a lower energy. We study two possibilities: (1) A significant number of baryons will, through the weak interaction, convert to hyperons. (2) Hadronic matter may convert to quark matter in the interior where the pressure is high. In either case, the resulting softer equation of state will not support as large a range of stars in either gravitational mass or baryon number. Therefore, beyond the baryon number of either of the above equilibrated sequences there is a significant range of proto-neutron stars that possess no hydrostatically stable configurations after neutrino loss. They will subside into a black hole on the timescale of neutrino loss, similar to 10 s and after the processed material of the presupernova star has been ejected. The uncertainty as to which of the two possibilities for the ground state actually holds is due mainly to the imperfect description available for the quark matter phase of cold charge-neutral baryonic matter. We discuss these mechanisms in connection with the apparent absence of a neutron star in SN 1987A and the possible deficit of neutron star-supernova associations.