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.