  Core radii of globular clusters in the Large and Small Magellanic Clouds show
an increasing trend with age. We propose that this trend is a dynamical effect
resulting from the accumulation of massive stars and stellar-mass black holes
at the cluster centers. The black holes are remnants of stars with initial
masses exceeding 20-25 solar masses; as their orbits decay by dynamical
friction, they heat the stellar background and create a core. Using analytical
estimates and N-body experiments, we show that the sizes of the cores so
produced and their growth rates are consistent with what is observed. We
propose that this mechanism is responsible for the formation of cores in all
globular clusters and possibly in other systems as well.
