What is the layered structure of an Asymptotic Giant Branch (AGB) star core post-helium exhaustion?
Answer
Inert carbon/oxygen core, surrounded by helium and hydrogen fusing shells.
When the helium fuel is completely exhausted from the core of a star that has completed its horizontal branch phase, the core becomes inert, consisting of carbon and oxygen. Fusion continues in two distinct shells surrounding this inert center: a layer immediately above the C/O core fuses helium into heavier elements, and an outer layer fuses hydrogen into helium. This dual-shell burning structure causes the star to expand dramatically again, even larger than its first red giant phase, placing it on the Asymptotic Giant Branch (AGB).
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