Immense numbers (1057) of extremely energetic neutrinos are emitted in just 10 seconds by type II supernovae when the highly compressed iron-56 core of a large and spent star can no longer support itself against the crush of gravity, and collapses. The electrons of the iron are forcibly captured by the protons, transmuting them into neutrons and releasing neutrinos, a process of forced electron capture. A neutron star with a diameter of just 10 - 30km is born. Ten times more energy is emitted as neutrinos than photons. The iron-56 outer layers of the star are ejected by the blast. Some of the emitted neutrinos are absorbed by the ejected iron-56 to form first cobalt-56 then nickel-56. This process is the reverse of inverse beta decay. The newly created nickel-56 then decays back into cobalt-56 by inverse beta decay, emitting positrons, with a halflife of 6 days. The cobalt-56, itself a positron emitter, decays by inverse beta decay back into iron-56 with a halflife of 77 days and is responsible for the characteristic 77 day decay in luminosity of type II supernovae. It should also be noted, that because a supernova explosion converts stable iron-56 to inverse beta decaying nickel-56, that supernovas afterwards emit immense numbers of anti-electrons, or positrons, the intensity of which follows the same characteristic 77 day exponential reduction in intensity..

The emitted ultra high energy electron neutrinos (or -neutrinos) can be detected in real time on Earth yielding energy and directional information. The neutrinos interact with matter producing electrons (or muons, heavy electrons), which, in traversing a transparent medium (sea water or glacier ice have been used) faster than can light (which in water travels at 0.75c), emit shock-wave cones of blue light (Cerenkov radiation) which are detected by photomultipliers. The threshold neutrino energy for this reaction is 7.5MeV. 26 such neutrinos were detected from supernova SN1987A in 1987. The neutrinos produced in a supernova explosion are generated before the light is, so detecting the neutrinos gives optical astronomers about an hours warning to observe the explosion.