RED-SUPERGIANT and SUPERNOVA RATE PROBLEMS: IMPLICATION for the RELIC SUPERNOVA NEUTRINO SPECTRUM

Direct observations of core-collapse supernovae (SNe) and their red supergiant (RSG) progenitors suggest that the upper mass limit of RSGs may be only about 16.5-18MȮ, while the standard theoretical value is as much as 25MȮ. We investigate the possibility that RSGs with m >16.5-18MȮ;end their lives as failed supernovae (fSNe) and analyze their contribution to the relic supernova neutrino spectrum. We show that adopting this mass limit simultaneously solves both the RSG problem and the supernova rate problem. In addition, energetic neutrinos that originated from fSNe are sensitive to the explosion mechanism, and in particular, to the nuclear equation of state (EOS). We show that this solution to the RSG problem might also be used to constrain the EOS for failed supernovae.