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 at the moment is currently fusing hydrogen in its core. This gives an outward pressure that prevents the Sun from shrinking due to gravity. At the moment it’s in balance with each other.

When the hydrogen at the core runs out fusion will slow and the outward pressure will drop. This will allow the Sun to shrink in size. This inward crushing pressure will raise the, well, pressure in the core and also the temperature. This will then allow elements beyond hydrogen to start to fuse. This will create more outward pressure than the fusing of hydrogen did and so the Sun will expand.