  The collapse time for a cluster of equal-mass stars is usually stated to be
either 330 central relaxation times ($\trc$) or 12--19 half-mass relaxation
times ($\trh$). But the first of these times applies only to the late stages of
core collapse, and the second only to low-concentration clusters. To clarify
how the time depends on the mass distribution, the Fokker-Planck equation is
solved for the evolution of a variety of isotropic cluster models, including
King models, models with power-law density cusps of $\rho\sim r^{-\gamma}$, and
models with nuclei. High-concentration King models collapse faster than
low-concentration models if the time is measured in units of $\trh$, but slower
if it is measured in units of $\trc$. Models with cusps evolve faster than King
models, but not all of them collapse: those with $0<\gamma<2$ expand because
they start with a temperature inversion. Models with nuclei collapse or expand
as the nuclei would in isolation if their central relaxation times are short;
otherwise their evolution is more complicated. Suggestions are made for how the
results can be applied to globular clusters, galaxies, and hypothetical
clusters of dark stars in the centers of galaxies.
