When is a group of stars not a galaxy?

Omega Centauri is facing an identity crisis, as an online poll is set up to decide how to distinguish between dwarf galaxies and star clusters

URL: http://feeds.newscientist.com/c/749/f/10898/s/120c4685/l/0L0Snewscientist0N0Carticle0Cdn20A0A260Ewhen0Eis0Ea0Egroup0Eof0Estars0Enot0Ea0Egalaxy0Bhtml0DDCMP0FOTC0Erss0Gnsref0Fspace/story01.htm