Red Giant National Schools Observatory

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Wiki info

When the star exhausts the hydrogen fuel in its core, nuclear reactions can no longer continue and so the core begins to contract due to its own gravity. This brings additional hydrogen into a zone where the temperature and pressure are sufficient to cause fusion to resume in a shell around the core. The hydrogen-burning shell results in a situation that has been described as the mirror principle; when the core within the shell contracts, the layers of the star outside the shell must expand. The detailed physical processes that cause this are complex, but the behaviour is necessary to satisfy simultaneous conservation of gravitational and thermal energy in a star with the shell structure. The core contracts and heats up due to the lack of fusion, and so the outer layers of the star expand greatly, absorbing most of the extra energy from shell fusion. This process of cooling and expanding is the subgiant star. When the envelope of the star cools sufficiently it becomes convective, the star stops expanding, its luminosity starts to increase, and the star is ascending the red-giant branch of the Hertzsprung–Russell (H–R) diagram.


Red Giant National Schools Observatory
Red Giant National Schools Observatory
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Life Cycle of a Star National Schools Observatory
Life Cycle of a Star National Schools Observatory
Life Cycle of a Star National Schools Observatory
Life Cycle of a Star National Schools Observatory
Life Cycle of a Star National Schools Observatory
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Image of the Month May 2017 National Schools Observatory
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Life Cycle of a Star National Schools Observatory
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Life Cycle of a Star National Schools Observatory
Life Cycle of a Star National Schools Observatory
Life Cycle of a Star National Schools Observatory
Life Cycle of a Star National Schools Observatory
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Life Cycle of a Star National Schools Observatory
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Neutron Stars National Schools Observatory
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Life Cycle of a Star National Schools Observatory
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Life Cycle of a Star National Schools Observatory
Astronomy at Yale on Vimeo
Astronomy at Yale on Vimeo
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Star Sizes National Schools Observatory
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Life Cycle of a Star National Schools Observatory
Life Cycle of a Star National Schools Observatory
Life Cycle of a Star National Schools Observatory
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Life Cycle of a Star National Schools Observatory
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Pulsar National Schools Observatory
Pulsar National Schools Observatory