Eli5. Our sun will expand to an orange giant in the future. Why is that?

Question

I have read that it has something to do with the depletion of fuel. Seems like the star would collapse rather than shrink.

In: 105

Answer 1

The sun is a gigantic explosion contained by it’s own gravity. Less mass means bigger blast size due to less gravity pull. Afterwards less fuel will be minor blast and will get the mass to contract in itself shrinking. We are talking about millions of years though.

I’m not astrophysics, just how I understand it.