How does a star like a Red Dwarf ($0.1 M_{ ext{suns}}$) manage its extremely long main sequence life?
Answer
Its core remains cooler and dimmer, allowing it to sip fuel extremely slowly
Red dwarfs, characterized by very low masses around $0.1$ times that of the Sun, exhibit exceptional longevity on the main sequence precisely because of their low energy demands. Unlike massive stars, their cores operate at much lower temperatures and pressures, resulting in a dramatically reduced luminosity. This allows them to sustain hydrogen fusion at an incredibly frugal rate. They are so efficient and slow in their consumption that their predicted main sequence lifetimes extend into the hundreds of billions or even trillions of years, far surpassing the current age of the universe.
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