Like cosmic bumper cars, four galaxies are ramming into each other in one of the biggest collisions ever recorded. The quartet will ultimately merge into a single galaxy that may be several times as massive as the Milky Way.
Kenneth Rines of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and his colleagues spotted a fan-shaped plume of stars, 150,000 light-years long, spilling from a compact group of four galaxies in a cluster known as CL0958+4702. The cluster lies 5 billion light-years from Earth. Three of the galaxies weigh about the same as the Milky Way, while the fourth is about three times as massive.