Record-breaking galactic tail discovered near doomed galaxy group.
Astronomers have discovered a gas tail stretching over a million light-years long behind galaxy group NGC 4839, which is merging with the much larger Coma Cluster. Using X-ray data from NASA's Chandra X-ray Observatory and optical data from the Sloan Digital Sky Survey, scientists measured the tail as NGC 4839 moved through the Coma Cluster. The tail is the longest such structure ever observed and is burning especially bright, giving astronomers a rare opportunity to study it in more detail and learn more about the mechanics of how galaxy clusters merge.