Scientists Spy Galactic “Traffic Jam"

Astronomers have spotted a rare, complex cosmic collision of four galaxy clusters 5.4 billion light-years from Earth. A spectacular composite image from NASA's Chandra X-Ray Observatory and Hubble Space Telescope revealed the pileup—and its likely source.

This composite image shows the massive galaxy cluster MACSJ0717.5+3745, where four separate galaxy clusters have been involved in a collision, the first time such a phenomenon has been documented. Hot gas is shown in an image from NASA's Chandra X-ray Observatory and galaxies are shown in an optical image from NASA's Hubble Space Telescope.
Credit: X-ray (NASA/CXC/IfA/C. Ma et al.); Optical (NASA/STScI/IfA/C. Ma et al.)

A nearby filament of galaxies is driving the pileup. The hot gas shows that the filament is falling into the clusters causing the collisions and driving the cluster's evolution.