The Virial Theorem

The Kelvin-Helmholtz timescale discussed in the left frame is a special case of a more general relation called the Virial Theorem. This powerful mathematical theorem governs how the gravitational energy and heat energy of a star must be related.

The Virial Theorem involves theoretical ideas that go beyond the scope of our discussion, so we will not describe it. However, various things that we discuss will in fact depend implicitly on this theorem. Examples include the collapse timescales discussed in the left panel and determination of the mass present in the center of large galaxies.