What is the composition of the innermost structure of a Sun-like star immediately after the core helium burning phase is complete?
Answer
A degenerate carbon and oxygen core
Following the Helium Flash and the subsequent, shorter period of core helium burning, the fuel supply of helium is finally exhausted in the center of the star. The resulting stellar ash at the very heart of the star is composed of the products of that fusion: carbon and oxygen. This central region, which is now inert regarding helium fusion, becomes a degenerate carbon/oxygen core. Surrounding this core, the star maintains a complex, layered structure, including a shell of helium fusion converting He to C/O, which is itself surrounded by an outer shell still burning hydrogen into helium.
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