Mayall II = G1 in M31: Giant Globular Cluster or Core of a Dwarf Elliptical Galaxy?

?????At the moment, only the anticorrelation of metallicity with age recently observed in ? Centauri suggests that this cluster enriched itself over a timescale of about 3?Gyr. This contradicts the general idea that all the stars in a globular cluster are coeval and may favor the origin of ? Centauri as being the remaining core of a larger entity, e.g., of a former nucleated dwarf elliptical galaxy. In any case, the very massive globular clusters, by the mere fact that their large masses imply complicated stellar and dynamical evolution, may blur the former clear (or simplistic) difference between globular clusters and dwarf galaxies.