The current and accepted theory of the life of our Sun is that it is about 4 or 5 billion years old. In about another 4 to 5 billion years time it will dramatically change.
As hydrogen fuel is consumed the Sun will expand and maybe engulf the Earth. It will eventually reach a point of maximum and then compact into a dwarf.
What is the physics behind the initial expansion?
Currently there is a balance that maintains the Sun's size. Without the huge energy output the Sun would collapse to a fraction of its current size under gravitational pressure. This is what confuses me. Once H2 becomes depleted I imagine the Sun would shrink but the converse is what scientists believe is to happen.
Why is it so?
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