Astronomers have argued for years over whether massive galaxies form from scratch, or by chunking together smaller galaxies.
Lately, evidence is building for the latter theory, and a new study adds to the growing picture of galaxy formation as a clumpy affair. Using an array of both ground-based and space telescopes, including ESO's Very Large Telescope in Chile and the Hubble Space Telescope, a team of astronomers recently observed groups of huge galaxies in the process of merging, showing that large, established galaxies can still grow bigger
More: http://www.space.com/scienceastronomy/080915-mm-galaxy-formation.html