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This image from the Hubble Space Telescope shows the rich galaxy cluster Abell 3827. The strange blue structures surrounding the central galaxies are gravitationally lensed views of a much more distant galaxy behind the cluster. Observations of the central four merging galaxies have provided hints that the dark matter around one of the galaxies is not moving with the galaxy itself, possibly implying dark matter-dark matter interactions of an unknown nature are occuring. The dark matter is currently 5 000 light-years (50 000 million million kilometers) behind the galaxy – it would take NASA's Voyager spacecraft 90 million years to travel that far. Dark matter has never before been observed interacting in any way other than through the force of gravity.
Image Credit: ESO
Image enhancement: Jean-Baptiste Faure