  Utilizing a series of N-body simulations, we argue that gravitationally bound
stellar clusters of modest population evolve very differently from the picture
presented by classical dynamical relaxation theory. The system's most massive
stars rapidly sink towards the center and form binary systems. These binaries
efficiently heat the cluster, reversing any incipient core contraction and
driving a subsequent phase of global expansion. Most previous theoretical
studies demonstrating deep and persistent dynamical relaxation have either
conflated the process with mass segregation, ignored three-body interactions,
or else adopted the artificial assumption that all cluster members are single
stars of identical mass. In such a uniform-mass cluster, binary formation is
greatly delayed, as we confirm here both numerically and analytically. The
relative duration of core contraction and global expansion is effected by
stellar evolution, which causes the most massive stars to die out before they
form binaries. In clusters of higher N, the epoch of dynamical relaxation lasts
for progressively longer periods. By extrapolating our results to much larger
populations, we can understand, at least qualitatively, why some globular
clusters reach the point of true core collapse.
