If the gamma rays take 1 million years to get out, couldn the Sun have already burned out (i.e. fusion stopped) a long time ago?
We know that nuclear fusion is still going on quite healthily in the solar core because we see neutrinos coming from the Sun- neutrinos from the core just cruise right through the layers of the Sun and we can detect them in “real time”. Actually, for quite a while in the latter half of the last century there was a “solar neutrino problem”: fewer neutrinos were observed from the Sun than expected. Some people thought this might be because the Sun’s fusion was shutting down, and that we could be in trouble within a million years or so! But by about 2001 it was known that the reason for the apparent deficit is that neutrinos are changing (“oscillating”) into a type which is harder to observe. It was in fact the Sudbury Neutrino Observatory in Canada which showed definitively that the full expected flux of neutrinos from solar fusion is indeed coming out of the Sun.
