Metastability of protoneutron stars in the extended Zimanyi-Moszkowski model

We have investigated the protoneutron star (PNS) using the extended ZimanyiMoszkowski relativistic mean-…eld model of hadronic matter with and without antikaon condensation. The trapped neutrinos in PNS delay the appearance of negative-charged hadrons or K , and so its equation of state becomes rather sti¤er than neutrino-free neutron star (NS) at high baryon densities. As the results, the maximum gravitational and baryonic masses of PNS are larger than those of NS. Thus, there exists metastable PNS that might collapse to a low-mass black hole after deleptonization. However the careful analyses of hadron composition reveal that the central baryon density of the lightest metastable PNS is lower than the density above which the negative-charged hadrons appear. Consequently, the PNSs, in which the negative charges are carried by leptons only, can be also metastable. 1 Introduction The supernova explosion SN1987A [1] o¤ered a unique opportunity to verify for the …rst time our knowledge of astronomy and astrophysics using various detection techniques. It was con…rmed that the neutrino-trapped compact object, the protoneutron star (PNS), was initially produced and then cooled o¤ through the radiation of neutrinos. However there is no evidence until now [1] that the deleptonized cold neutron star (NS) is formed after neutrino burst. It was therefore suggested [2] that the delayed collapse of PNS to a low-mass black hole (BH) had happened. Such a possibility was also investigated by Bombaci [3] in terms of baryonic masses of PNS and NS because the baryon number is conserved in PNS during its cooling through deleptonization. It has been shown that the delayed collapse to BH cannot occur if the PNS and NS are composed of nucleons and leptons only. On the contrary, a lowmass BH will be formed if the negative charges in PNS and NS are carried by hadrons This paper is the revised version of mp_arc 05-243, whose programing code of numerical calculation unfortunately had a few bugs so that the spin degeneracy of neutrino was 2 rather than 1. Although the …gures in section 3 are modi…ed, our main results are not a¤ected.