Some criteria for mass ejection by stars undergoing gravitational collapse

Some criteria necessary for a gravitationally collapsing stellar core to eject its envelope in a supernovalike explosion are examined. In particular, neutrino transfer of momentum and energy from the core to the mantle is explored in detail. Necessary conditions for a core bounce to give a strong reflected shock are also discussed. In order for the neutrinos to be effective in ejecting material by momentum transfer, their luminosity must be greater than, or comparable to, the 'Eddington limit' for neutrinos, with neutrino energies not less than about 15 MeV. In order for neutrino energy transfer to be important, not only must the neutrino flux be high but also the neutrino energies must be at least around 26 MeV. A core bounce requires a large change in the adiabatic index. Comparisons with detailed model calculations are made which indicate that these suggested criteria are appropriate. Some implications of these results are discussed.