Galaxy clusters can contain hundreds of galaxies, and the ones at their centers are the largest galaxies known to astronomers. These huge objects are the product of successive mergers between smaller galaxies, a process that has exhausted the raw materials for the formation of stars.
That is, in every case but one—a new set of observations have revealed one of the largest and hottest galaxy clusters yet seen, and its central galaxy has an unexpectedly high rate of star formation. This finding may provide new insights into the history of galaxy clusters, and the formation of structure in the Universe.