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helium flashThe explosive onset of helium burning (by the triple alpha process) in the degenerate core of an evolved star (a giant) when the core temperature reaches about 108 kelvin. The sudden increase in energy production causes a rapid rise in temperature, in turn increasing the reaction rate, but this runaway process eventually removes the degeneracy and the reaction once again becomes sensitive to the gas pressure. The helium flash occurs in stars of about one to two solar masses.
helium flash[′hē·lē·əm ‚flash]
The onset of runaway helium burning in the degenerate core of a red giant star and the resulting expansion of the core.