This image of gravitationally magnified faint galaxies far in the distance behind a massive cluster of galaxies from the Hubble Space Telescope indicates that a huge ring of dark matter likely exists surrounding the center of galaxy cluster CL0024+17 that has no normal matter counterpart.
What is visible in the above image are spectacular galaxies that are part of CL0024+17 itself, typically appearing tan in color. Next, a close inspection of the cluster center shows several unusual and repeated galaxy shapes, typically more blue.
The computationally modeled dark matter ring spans about five million light years and been digitally superimposed to the image in diffuse blue. A hypothesis for the formation of the huge dark matter ring holds that it is a transient feature formed when galaxy cluster CL0024+17 collided with another cluster of galaxies about one billion years ago, "leaving a ring similar to when a rock is thrown in a pond" according to NASA experts.
Image credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)