How long can a red dwarf star, less massive than $0.25 M_ ext{Sun}$, potentially sustain hydrogen fusion?

Answer

About one trillion years

Red dwarfs are fully convective, allowing them to circulate nearly all their mass to the core for fusion, granting them lifespans significantly longer than the current age of the universe, estimated at about one trillion years.

How long can a red dwarf star, less massive than $0.25 M_	ext{Sun}$, potentially sustain hydrogen fusion?
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