Neutrino emission from a supernova shock

In the shock resulting from the 'bounce' of a supernova, the neutrinos are prevented from leaving by the high neutrino opacity of the material just outside the shock, until the density of that material has decreased to less than 10 to the 11th g/cu cm. The number of neutrinos then emitted is moderate. Neutrino pairs are formed, mainly from electron pairs, and their emission again is limited by the opacity. The energy lost from the shock by neutrino pairs is estimated, and is from 20 to 50% for reasonable initial shock energies.