This photo supplied by NASA-ESA shows a ring of what NASA says is dark matter, which measures 2.6 million light-years across, which was found in the cluster ZwCl0024+1652, located 5 billion light-years from Earth. An international team of astronomers using the Hubble Space Telescope has discovered the ghostly ring of dark matter that was formed long ago during a titanic collision between two massive galaxy clusters. It is the first time that a dark matter distribution has been found that differs substantially from the distribution of ordinary matter. Astronomers have long suspected the existence of the invisible substance of dark matter as the source of additional gravity that holds galaxy clusters together. Although astronomers don't know what dark matter is made of, they hypothesize that it is a type of elementary particle that pervades the Universe.