Institute for Advanced Study / Princeton University Joint Astrophysics Colloquium

Stars in nearly all globular clusters show complex relations among the abundances of light elements (up to Na).  Many also show anti-correlations of Mg and Al.  Until now, only one cluster (M15) conclusively showed any star-to-star variation in neutron-capture elements, like Eu.  Using a trick of stellar evolution, I show that these variations are primordial, not caused by external pollution.  Then, I show that M92 also has variations in barium and lanthanide abundances (but not first-peak r-process) among the first generation of stars but not the second.  The evidence points to a rare source of the "main" r-process that happened right at the start of the formation of the cluster.