Because the time it takes such an 'n-body' system to collapse is measured in 10s of billions of years. A globular cluster is dynamically unstable because the core is gradually shrinking over time as stars are ejected from the core region into the halo of the system, and then lost from the cluster because of the tidal gravitational field of the Milky Way. 2 and 3 body encounters among stars in the core over time, cause most of the potential energy of the cluster to get locked up into a hand full of compact binary stars. This is called the gravito-thermal catastrophy. By the time this happens, most of the stars have been ejected from the cluster as they have picked up additional kinetic energy from the encounters with other stars in the core of the cluster. Eventually the number of stars, over tens of billions of years decreases from 100,000 to a few thousand, and by then you hardly notice the globular cluster at all.
Copyright 1997 Dr. Sten Odenwald
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