This composite image shows the massive galaxy cluster MACS J0717, where four separate galaxy clusters have been involved in a collision. This is 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. The hot gas is color-coded to show temperature, where the coolest gas is reddish purple, the hottest gas is blue, and the temperatures in between are purple. This galaxy cluster is located approximately 5.4 billion light-years from Earth.