Phil Plait has a really neat post on the evolution of spiral galactic bulges by means of dwarf cannibalization here.

It really is a neat piece of work, in which the astronomers in question took a look at a galactic cluster called Terzan 5 and discovered that it contains two populations of stars, an outer shell of older (red) stars, and an inner core of newer (blue) stars. This is interesting, yet disturbing, because if Terzan 5 is the remnants of a galaxy, then it is one pretty messed up galaxy. Assuming it is a dwarf galaxy, we can rule out that it is not a dwarf irregular, since they have no distinct shape, and Terzan 5 is spherical. We can rule out that it is a dwarf spiral for the same shape mismatch reason, and we can rule out that it is a dwarf elliptical or dwarf spheroidal, since it shows evidence of recent star formation.

Terzan 5 is probably an ultra compact dwarf galaxy, yet is shows a unique feature not known (AFAIK) to UCDs. The newer core of stars surrounded by a shell of older stars. Although this is a relatively unknown area of study, I would presume that ultra compact galactic nuclei contain a heterogeneous mixture of old and new star populations due to stellar interactions throughout their rather small core. Dr. Plait argues that the dual star populations imply that Terzan 5 is a dwarf core galaxy, but I am of the opinion that the younger stars should be on the outside, not the inside.

The one thing we both agree on is that the fact that the iron in stars in Terzan 5 matches the amounts of iron in stars in our galactic bulge. This is indicative of interactions within the two objects, although I am not convinced that it is because the Milky Way stripped Terzan 5 of its outer stars and added them to the bulge. It is a tantalizing mystery, one that can only be sure to add to the mystique of galactic evolution.