So yeah, it's a beefy cluster. Like most big clusters, it has a big galaxy sitting in its center. It doesn't have an official name, but astronomers call it Abell 2261 BCG, for Brightest Cluster Galaxy. In general, galaxies in the centers of clusters are the biggest and brightest; they're literally at the bottom of the cluster's gravity well, and everything falls into them. Mergers with smaller galaxies are common, so the central galaxy usually grows huge. In this case, the central galaxy is over a million light years across, hugely dwarfing our own Milky Way (which is about 120,000 light years wide).