Kelvin-Helmholtz timescale

Kelvin–Helmholtz timescale

The time taken for a mass of gas to collapse under its own gravitation. It is given by
τKH = GM 2/RL
where G is the gravitational constant and M, R, and L are the mass, radius, and luminosity of the object. It is thought to describe the evolutionary timescale of a pre-main-sequence star. Such a collapse – known as the Kelvin–Helmholtz contraction – was proposed in the late 19th century as the source of the Sun's energy output. This theory was abandoned when the contraction timescale of only 107 years was shown to be too short. The energy source was subsequently shown to originate in nuclear-fusion reactions.