Galaxy cluster MACS J0717, composite image. This massive galaxy cluster was formed when four separate galaxy clusters collided. The hot gases in this image are colourcoded to show temperature, red gases are coolest, purple are hotter and blue are the hottest. The collisions are a result of a 13 million light year long stream of galaxies and other matter flowing into an already crowded region. The galaxy cluster is located 5.4 billion light years from Earth in the constellation Auriga. Image obtained by combining data from the Advanced CCD Imaging Spectrometer on the Chandra Xray Observatory and the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) on the Hubble Space Telescope.