Galactic train wreck

Situated 2.4 billion light-years from Earth San Francisco - Arabstoday It looks like classic Star Trek meets golden-era disco dance floor, but actually we're looking at a visualisation of the dark matter and hot gas at the core of the galaxy cluster Abell 520. Situated 2.4 billion light-years from Earth, Abell 520 was formed by the cosmic train wreck of several smaller galaxy clusters. In the debris of this collision, astronomers found a massive dark core devoid of bright galaxies and which challenged basic theories of dark matter. This composite image combines data from three sources - NASA's Hubble Space Telescope, the Canada-France-Hawaii Telescope atop Mauna Kea, Hawaii, and NASA's Chandra X-ray Observatory - and confirms previous mappings of Abell 520's dark-matter core. The natural colour of the galaxies has been superimposed with starlight in orange and greenish areas of hot gas left over from the collision. It is the central blue on this map that shows the location of most of Abell 520's mass, in an area with some gas but few galaxies. This dense dark-matter core shows that the galaxies are not anchored to dark matter, even in a collision, as previously predicted.