Kelvin–Helmholtz mechanism

Summary

The Kelvin–Helmholtz mechanism is the heating and shining of a star or planet caused by its slow gravitational contraction. As the body shrinks, its gravitational energy decreases. By the virial theorem, about half of the released energy heats the interior and the other half is radiated away. It powers stars before they start nuclear fusion, and it explains why Jupiter emits more heat than it receives from the Sun. In the nineteenth century it was proposed as the energy source of the Sun. But the lifetime it gives, the Kelvin–Helmholtz timescale, is far shorter than the age of the Earth.