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Originally Posted by rtomes
I am also interested in the question of what proportion of the gravitational energy also comes from kinetic energy due to motion of matter (i.e relativistic mass increase). If I remember when I worked this out once before it was small compared with the radiant energy, but it would be nice to have this confirmed.
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No, the heat in the gas is about 100 times more than the radiant energy, so it will also contribute similarly more to the gravitational mass.
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Just to confirm how I got 10^-7, I assumed that the life of the Sun is about 10^10 years and that it converts 0.7% of its mass to radiant energy (although I suppose some goes to neutrinos) as a result of H --> He fusion.
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That might be a factor of 3 or something too high-- not all the H goes to He, only the H in the core.
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I used the 170,000 years to work out what proportion of the energy is in the Sun at any one time, surprisingly 0.0017% of what it ever produces.
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That's valid for a rough estimate. It's probably just a little high overall, but my calculation was also rough so it could easily be between the two.