The galaxy on the left, Abell 644, is in the center of a cluster of galaxies. The right panel contains SDSS J1021+131, a so-called field galaxy because it is isolated. Both images are composites with data from Chandra (blue) and the Sloan Digital Sky Survey (red, green, blue). 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.