The ring of background galaxy images , defocused by dark matter's gravity into a light blue haze , is 2.6 million light-years across. It was found in the cluster CL0024+17, located five billion light-years from Earth. A member of the team that spotted the dark matter ring, said they unexpectedly found the ring while mapping the distribution of dark matter within the cluster, by observing how its gravity bends the light of more distant background galaxies. Computer simulations of the gravitatonal refraction reveal that as the clusters collide, the dark matter falls to the centre of the combined cluster and "sloshes" back out. As the dark matter moves out, it begins to slow under the pull of gravity and pile up into the ripple that left this distinct footprint. The report has been accepted for publication in Astrophysical Journal.