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The article is using meteorites as an analogy; the model is of the Sun forming by gravitational contraction of a gas cloud, for which an r of infinity is approp

The article is using meteorites as an analogy; the model is of the Sun forming by gravitational contraction of a gas cloud, for which an r of infinity is appropriate. What's interesting is that the power available from solar fusion is of a similar order of magnitude to that available from gravitational contraction. But of course it must be, because if fusion was too powerful medium-mass stars wouldn't be able to form to provide light and heat to habitable worlds, and if it was too weak then giant stars wouldn't be able to overcome their gravitational binding energy in supernovae to disperse the elements that form habitable worlds.

pdonis 6y ago
> What's interesting is that the power available from solar fusion is of a similar order of magnitude to that available from gravitational contraction. No, it isn't; fusion provides much more energy per unit mass than gravitational contraction would for the Sun. As I calculated, gravitational contraction falling in from infinity to the current radius of the Sun provides about 2 x 10^11 Joules per kilogram. Fusion provides about 5 x 10^14 Joules per kilogram (the exact number depends on the particular fusion reaction).