Free Astronomy Magazine July-August 2023

26 JULY-AUGUST 2023 ASTRO PUBLISHING weighs the galaxies themselves. Much of the physics of galaxy clus- ters is well understood; however, observations of the earliest phases of formation of the ICM remain scarce. Previously, the ICM had only been studied in fully-formed nearby galaxy clusters. Detecting the ICM in distant protoclusters — that is, still-forming galaxy clusters – would allow astronomers to catch these clusters in the early stages of for- mation. A team led by Luca Di Mas- colo, first author of the study and researcher at the University of Tri- este, Italy, were keen to detect the A vast reservoir of hot gas in the Spiderweb protocluster by ESO − Juan Carlos Muñoz Mateos G alaxy clusters, as the name suggests, host a large num- ber of galaxies — sometimes even thousands. They also contain a vast “intracluster medium” (ICM) of gas that permeates the space be- tween the galaxies in the cluster. This gas in fact considerably out-