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Core collapse supernovae are violent explosions of massive stars. Explaining these cataclysmic events requires expertise in many areas of science, with nuclear physics playing a major role. During the collapse, most of the energy radiated by the star is in the form of an immense burst of neutrinos, elusive elementary particles which pass through ordinary matter almost undisturbed. Knowledge of neutrino propagation in the hot, dense supernova environment is essential for translating the neutrino signal detected on Earth into information about the innermost regions of the explosions and about the properties of neutrinos themselves.
There are three types of neutrinos, and they continuously oscillate (morph) from one kind into another. The figure shows the neutrino oscillation probability as a function of neutrino energy and the direction of emission from the surface of a collapsing star. Such simulations, involving the solution of nearly one million coupled nonlinear differential equations, demonstrate that the mass ordering of neutrinos may be determined via observations of neutrinos from supernovae and that extremely weak interactions between neutrinos may alter explosion mechanisms.