A Carbon Flash

Now one would expect that a carbon flash will happen. However this is not the case. The star expels its outer layers. When the Sun becomes an AGB star, its outer layer will engulf the terrestrial planets—the Earth would move in the atmosphere of the Sun. Because of g = GM/r, the acceleration due to gravity at the surface of a star with a mass of one solar mass and a radius of 100 R is only 1/10000 as strong as the gravity at the surface of the Sun. Such an object is quite unstable. The instability of such stars of such stars is enhanced by the strong dependence of the triple alpha process (conversion of three He into carbon) on temperature. Episodes of rapid energy release may occur and the star looses up to 30% of its initial mass. 

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This occurs suddenly, and is observed as a carbon flash. Figure 17.1. The star then either continues to bum carbon, or explodes (a supernova) with destmction of most of the star. 

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