Quote:
Originally Posted by Ken G
Let's look at that. I'd say that at any time about 1/100 of its internal energy is radiant, but the rest is related to gas pressure at a temperature of about 10 million K, which corresponds to protons moving at 1/1000 of the speed of light. So you have 100 times more energy in the proton motions, and 1 million times more energy in the proton rest mass than in their motions, so yes I get maybe 10-8 but that's not accurate enough to rule out 10-7.I think it would be fair to call this the "gravitational mass" of the Sun, for example. We are dropping factors of 2 and so forth right and left, but I think it's fair to say that up to 1 part in 10 or 100 million of the gravity that the Sun produces comes from the radiant energy in there at any moment.
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Hi Ken
Yes, the statement that the gravity comes from that energy is a nice way of putting it. 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.
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. 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. Of course there are some other processes after that, but I am guessing that the present rate of conversion is about an average for 10^10 years. That gave me an answer of 1.19*10^-7 which I figure is accurate to about 1 digit anyway.
Regards
Ray