Compact groups are small systems of 3-6 galaxies that are located very close together in space. These groups have existed for billions of years and may provide clues about how larger galaxy clusters form in the future as the galaxies in compact groups move even closer together over time. When galaxies are in such close proximity, they will eventually collide and merge together, disrupting the shapes of the original galaxies and sometimes triggering bursts of new star formation from the interacting gas clouds. One example is Stephan's Quintet, where evidence of a past galaxy collision can be seen in the long tail of material trailing from one of the galaxies.

1. The Universe's Good Neighbors: Compact Groups Ricardo Bilton and Kalei Sabaratnam

7. Resulting tail from galaxy collision