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What powers a star as it swells into a red giant after its core hydrogen runs out?

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  1. Hydrogen fusing in a shell around the core
  2. Iron fusing in the core
  3. Chemical burning of the outer layers

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References

  1. Astronomy 2e, 22.1 Evolution from the Main Sequence to Red Giants openstax.org/books/astronomy-2e/pages/22-1-evolution-from-the-main-sequence-to-red-giants Checked 2026-10-10.

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