MASS SEGREGATION RELAXATION, AND THE COULOMB LOGARITHM IN N-BODY SYSTEMS (AGAIN)

The question of the upper cutoff b(max) in the ''Coulomb logarithm'' for self-gravitating N-body systems has been reexamined, based on both large-scale mass segregation and cumulative squared changes in orbital energies as measures of relaxation. Simulations of greater scope than those of an earlier study of the authors, together with a more sophisticated statistical procedure for estimating b(max), unequivocally support the conclusion of that study-namely, b(max) has a roughly constant value comparable to the half-mass radius R, rather than a value is similar to N-1/3 R representative of the mean interparticle spacing that decreases with N. The ratios of the relaxation times observed in simulations using different softening lengths for the gravitational potential exhibit an N-dependence that agrees quantitatively with the postulate b(max) almost-equal-to R, but is conspicuously inconsistent with b(max) almost-equal-to N-1/3 R. These findings do not corroborate those of Smith (1992).