Mass segregation was one of the early important results to emerge from computer N-body simulations of clusters with a few dozen members. The heavier stars would gradually settle towards the center, increasing their negative binding energy. Lighter stars would preferentially populate the halo, with reduced binding energy. Later, direct integrations using many hundreds of stars showed the same tendency, as did models which integrated the Fokker–Planck equation for many thousands of stars.

We would expect this behavior from the basic properties of gentle relaxation by two-body encounters. Equation (14.65) shows that the timescale for dynamical friction to significantly decrease the energy of a massive star of mass M0 is less than the relaxation timescale ρR for lighter stars of mass m(moving with the same velocity) by a factor m/M0. As massive stars in the outer regions of a cluster lose energy to the lighter ones, they fall toward the center and increase their velocity. The massive stars continue to lose the kinetic energy they gain by falling, and continue to fall. The lighter stars, on the other hand, increase their average total energy and move into the halo. As light stars rise through the system, their velocity decreases, altering the local relaxation time for remaining massive stars. The net relaxation for any individual star will therefore involve an average of τR over its orbit.