What is the primary energy source for a white dwarf once it has settled into its final state?

Answer

Residual, stored thermal energy.

Crucially, nuclear fusion shuts down in a white dwarf; it shines solely by slowly radiating away the heat it retained from its previous stellar phases.

What is the primary energy source for a white dwarf once it has settled into its final state?

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The Ultimate Guide to Star Types: Dwarfs, Giants & Supergiants

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