  We propose an approach to find out when a self-gravitating system is in a
quasi-equilibrium state. This approach is based on a comparison between two
quantities identifying behavior of the system: a measure of interactions
intensity and the area. Gravitational scattering cross section of the system,
defined by using the two-particle scattering cross section formula, is
considered as the measure of interactions intensity here. A quasi-equilibrium
state of such system is considered as a state when there is a balance between
these two quantities. As a result, we obtain an equation which relates density
and temperature for such a system in the non-relativistic classical limit. This
equation is consistent with the TOV equation as expected.
