Primordial binaries and globular cluster evolution

MANYof the globular clusters in our Galaxy have probably undergone core collapse, and are currently re-expanding^1,2. This re-expansion requires a central energy source. Previously proposed mechanisms are either inefficient or may produce unacceptably bright cores³. Here we explore the most conservative solution to this problem. We suggest that primordial binaries, for which there is now direct evidence^4-6, could provide the necessary energy. We show that this mechanism leads to relatively large core sizes, containing ∼1% of the total cluster mass. Such a cluster would have a resolvable core (with a size of the order of arcseconds) which would consist mostly of binaries.