X-ray and Optical Images of Galaxy Cluster Abell 644
Abell 644 is in the center of a galaxy cluster that lies about 920 million light years from Earth. At the center of this galaxy is a growing supermassive black hole, called an active galactic nucleus (AGN) by astronomers, which is pulling in large quantities of gas.
(Credit: X-ray: NASA/CXC/Northwestern Univ/D.Haggard et al, Optical: SDSS)

X-ray and Optical Images of Field Galaxy SDSS J1021+131
This is an isolated, or "field," galaxy named SDSS J1021+1312, which is located about 1.1 billion light years away A survey of these and hundreds of other galaxies tells scientists how often the biggest black holes in field galaxies like SDSS J1021+131 have been active over the last few billion years. This has important implications for how environment affects black hole growth.
(Credit: X-ray: NASA/CXC/Northwestern Univ/D.Haggard et al, Optical: SDSS)