Musketball galaxy cluster. Composite image showing the Musketball cluster, where 700 million years previously a violent collision between two galaxy clusters wrenched 'normal' matter apart from dark matter. This cluster lies around 5.2 billion light years from Earth. Here, hot gas observed with NASA's Chandra X-ray Observatory is coloured red, whilst the galaxies in the optical image observed by the Hubble Space Telescope (HST) appear as mostly white and yellow. The location of the majority of the matter in the cluster (dominated by dark matter) is coloured blue. When the red and the blue regions overlap, the result is purple as seen in the image. The matter distribution is determined by using data from the Subaru Telescope, HST and the Mayall Telescope