Pre-Supernovae

Example data from Odrzywolek&Heger (2010)

Massive stars are probably the very next target for Galactic neutrino astronomy. Possibility of supernova prediction and monitoring of a star before, during and after explosion drives imagination.

After end of the core helium burning, massive star enters so-called neutrino-cooled stage. Because of groving temperatures tiny but essential fraction of positrons is established. Positrons are created as electron-positron pairs from high energy tail of thermal distribution. Usually, positrons immediately annihilate into photons, and energy is returned into thermal ensemble. Hovewer, in the standard model of electroweak interactions another annihilation product is possible: neutrino-antineutrino pair. In contrast to photons, neutrinos escape core of a star and energy is lost.

Detailed calculations show surprising efficiency of this pair-ahhihilation neutrino process. Actually, beginning with core carbon burning, neutrino luminosity is much larger than visible photon luminosity. During final stages of evolution, oxygen and silicon burning, neutrino luminosity exceed photon luminosity by many orders of magnitude. Visible in the electromagnetic radiation surface of a star provides negligible fraction of total radiation.

Pair-annihilation is prototype thermal neutrino cooling process. Three "classical" thermal processes are: pair, plasma and photo. Few other processes of minor importance, e.g. neutrino de-excitation of nuclei and brehmsstrahlung also do operate.

Beginning with oxygen burning, another class of neutrino cooling processes becomes progresively more important: weak nuclear transitions. Well known example of weak nuclear neutrinos is provided by the Sun . Usually, main sequence, He, C and Ne burning stars emit small amount of nuclear electron neutrinos. For example, solar neutrino flux is mere 2% of the photon luminosity. This is due to slowness of these weak processes.