How do Stars Shine?
The energy output of the Sun is 4x10
33
erg/s = 4x10
20
megawatts
If the Sun were burning coal or gasoline, it could last a few
thousand years (which used to be OK)
Gravitational contraction is an energy source (gravitational
potential energy can be quite potent): could last 10 million years
(this IS the source for young stars, brown dwarfs, or black holes)
The required shrinkage would be barely noticeable…
