Two examples of galaxy pairs in the COSMOS survey. The Hubble Space Telescope images show galaxies undergoing a close encounter (shown in gold). X-rays, as detected by Chandra, indicate which of the two galaxies hosts an AGN. In addition, diffuse X-ray emission from hot gas is present thus highlighting that such galaxy associations tend to reside in galaxy groups, an environment of rapid galaxy and black hole growth. Credit: Chandra X-ray Center