University of Virginia, College and Graduate School of Arts and Sciences

Building a Cluster of Galaxies - the Shocking Truth!

December 20, 2019

A group of astronomers, including U.Va.'s Craig Sarazin, have observed two groups of galaxies slamming into one another at a speed of about 4 million miles per hour.  The colliding groups will eventually merge and form a single cluster of galaxies; these are the largest objects in the Universe.  Clusters contain as much material as one million, billion stars.  This cosmic train wreck was observed with a number of space and ground-based observatories, including by U.Va. astronomers using the Apache Point Observatory (APO) in New Mexico.  U.Va. is a member of APO.  The picture above shows a composite of the X-ray and optical images of the merging groups.  These observations were the subject of an image press release by NASA's Chandra X-ray Observatory, which contains much more information and many more images.  There is also a video about this collision on YouTube at