The Phoenix galaxy cluster contains the first confirmed supermassive black hole that is unable to prevent large numbers of stars from forming in the core of the galaxy cluster where it resides. The Phoenix Cluster system has several distinct elements that help tell the story of its unusually high star formation. Data from NASA’s Chandra X-ray Observatory show that the coolest gas it can detect is located near the center of the cluster. In the absence of significant sources of heat, astronomers expect cooling to occur at the highest rates in a cluster’s center, where the densest gas is located.

The Phoenix Cluster (SPT-CL J2344-4243) is a massive, type I galaxy cluster located at its namesake constellation, the southern constellation of Phoenix. It was initially detected in 2010 using the Sunyaev–Zel’dovich effect by the South Pole Telescope collaboration. It is one of the most massive galaxy clusters known, with the mass on the order of 2×10¹⁵ M_☉. Most of the mass of the Phoenix Cluster is in the form of dark matter and its intracluster medium. The vast stellar halo of the Phoenix Cluster central galaxy extends to over 1.1 million light years from the center, making it one of the largest galaxies known. It is 22 times the diameter of our galaxy, and its starburst activity suggests that the galaxy is still growing larger.