What event typically causes a star like our Sun to swell up and become much brighter late in its life cycle?

Answer

It exhausts its core hydrogen, leading to expansion as a red giant.

When a star shifts its life cycle after exhausting core hydrogen, it often expands dramatically, increasing its size and significantly inflating its luminosity, as seen when the Sun becomes a red giant.

What event typically causes a star like our Sun to swell up and become much brighter late in its life cycle?

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