helium shell flash
helium shell flashA violent outburst of energy that occurs periodically in a highly evolved giant star. The star is producing energy in a shell of hydrogen and in an inner shell of helium surrounding the inert dense core of carbon and oxygen. Helium shell burning is unstable, producing energy mainly in short intense flashes. After a shell flash, which causes the star to expand then cool, the convective region in the outer part of the star goes deeper and may dredge up carbon to the surface.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006