The dense stream of massless neutrinos flowing away from a collapsed supernova core disturb each other, giving rise to collective oscillatory effects. The importance of these nonlinear phenomena was only recently recognised and studied.
A supernova marks the end of a massive star's life. When a massive star dies, it makes a spectacular exit – the most powerful explosion known to occur in the Universe.
Further details: The neutrinos from core-collapse supernovae