Is there a Size Difference between Red and Blue Globular Clusters?
  Blue (metal-poor) globular clusters are observed to have half-light radii
that are ~20% larger than their red (metal-rich) counterparts. The origin of
this enhancement is not clear and differences in either the luminosity function
or in the actual size of the clusters have been proposed. I analyze a set of
dynamically self-consistent Monte Carlo globular cluster simulations to
determine the origin of this enhancement. I find that my simulated blue
clusters have larger half-light radii due to differences in the luminosity
functions of metal-poor and metal-rich stars. I find that the blue clusters can
also be physically larger, but only if they have a substantial number of black
holes heating their central regions. In this case the difference between
half-light radii is significantly larger than observed. I conclude that the
observed difference in half-light radii between red and blue globular clusters
is due to differences in their luminosity functions and that half-light radius
is not a reliable proxy for cluster size.
