Subgiant - Subgiant, Red Giant, Supergiant All through the...

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Subgiant, Red Giant, Supergiant All through the long main sequence stage, the relentless compression of gravity is balanced by the outward pressure from the nuclear fusion reactions in the core. Eventually the hydrogen in the core is all converted to helium and the nuclear reactions stop. Gravity takes over and the core shrinks. The layers outside the core collapse too, the ones closer to the center collapse quicker than the ones near the surface. As the layers collapses, the gas compresses and heats up. Eventually, the layer just outside the core called the "shell layer" gets hot and dense enough for fusion to start. The fusion in the layer just outside the core is called shell burning . This fusion is very rapid because the shell layer is still compressing and increasing in temperature. The luminosity of the star increases from its main sequence value. The gas envelope surrounding the core puffs outward under the action of the extra outward pressure. As the star begins to expand it becomes a
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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Subgiant - Subgiant, Red Giant, Supergiant All through the...

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