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physical phenomena > energy source > exothermic fusion process > helium burning > helium flash

helium flash
subject			fact

helium flash	has minimum temperature 108 K
	has definition The onset of runaway helium burning under degenerate conditions. The helium flash occurs in the hydrogen-exhausted core of a star in the red-giant phase of evolution. When gravitational pressure has brought the degenerate core to a temperature of about 108 K, the helium nuclei can start to undergo thermonuclear reactions. Once the helium burning has started, the temperature builds up rapidly (without a cooling, stabilizing expansion), and the extreme sensitivity of the nuclear reaction rate to temperature causes the helium-burning process to accelerate. This in turn raises the temperature, which further accelerates the helium burning, until a point is reached where the thermal pressure expands the core and thus removes the degeneracy and limits the flash. The helium flash can only occur when the helium core is less than the 1.4 Msun Chandrasekhar mass limit and thus it is restricted to low-mass stars.
	is a kind of helium burning
helium burning	has duration 5 × 105 years
	has optimum density 700 g/cm3
	requires minimum mass at star birth 0.5 solar masses
	has optimum temperature 2 × 108 K
	has part product carbon
	has next higher temperature reaction carbon burning
	has product carbon, oxygen
	has reactant helium
exothermic fusion process	liberates energy
fusion	has antonym fission
	produces energy
	has reaction probability
	has catalyst
physical process	has domain physics

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