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Kelvin-Helmholtz timescale

(KH timescale, KH time, τKH, Kelvin-Helmholtz time, thermal timescale)
(time that would radiate away a body's heat energy given its luminosity)

A body's Kelvin-Helmholtz timescale (aka KH timescale, Kelvin-Helmholtz time, KH time or τKH and sometimes the term thermal timescale is taken to mean the same) is a simplified (back-of-the-envelope) calculation of the time a body could continue to shine as it does given its potential energy and kinetic energy (i.e., through the Kelvin-Helmholtz mechanism), but varying definitions are used:

These are within the same order-of-magnitude, given the virial theorem. They do not take into account any luminosity variation.

 τKH = K/L = (-U/2)/L
or alternately:
 τKH = U/L
or treating the object as a uniform-density sphere:
 τKH = 3GM²/(5RL) ≈ GM² /(RL)

I've also seen the term thermal timescale used regarding a different process.

Further reading:

Referenced by pages:
Kelvin-Helmholtz mechanism