Estimate the gravitational energy in the Sun, using eqs. (22.1)

and (22.2)

assuming that the mass is distributed uniformly. Can you confirm the statement in the text that gravitational potential energy could only power the Sun at its present luminosity for ?10⁷ y?? At what rate would the radius of the Sun have to be decreasing (in, say, mm/s) if its luminosity came from gravitational potential energy?

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Мо — 1.989 х 1030 kg