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 so near to each other, collisions are inevitable, which can disrupt the shapes of the galaxies and sometimes trigger bursts of new star formation as the gas clouds within the galaxies interact. One example is Stephan's Quintet, where the interaction between galaxies has created a long tail structure.

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

7. Resulting tail from galaxy collision