What would be the approximate luminous lifetime of the Sun if it derived its energy entirely from gravitational contraction?

Question

Quizplus · Accepted Answer

If the Sun derived its energy entirely from gravitational contraction, its luminous lifetime would be approximately 100 million years. This is because the Sun's gravitational energy would be converted into heat energy, which would radiate away as light, gradually reducing the size and temperature of the Sun. However, this is not the actual source of the Sun's energy, which comes from fusion reactions in its core and is expected to last for another 5 billion years.

What Would Be the Approximate Luminous Lifetime of the Sun