What would happen, if I were to trap the Sun in an almost perfectly reflective spherical mirror? I'm assuming this would accelerate the life of the sun and reduce the timescale required to turn it into a dwarf. How could I roughly estimate this timescale speed-up, if one occurs?
I'm assuming, of course, that the mirror is large enough to fit the sun in any of its giant phases.
It would reduce the star's ability to cool off the heat it produces in its core, so the star would heat up. As the star heats up, it grows, becoming less dense in the process. The drop in density reduces the rate of fusion within the star's core.
As such, you would not destroy the star, but rather conserve it, since it now takes a longer time to burn through its fuel.
Actually, this reduction in fusion rate on expansion is precisely what makes stars self-controlled fusion reactors. If it were the other way round with fusion gaining speed as density decreases, stars would not be able to form in the first place. They would simply blow up once they are heavy enough to begin fusion.
