A new study raises questions about the ring of dark matter reported to exist inside a galaxy cluster.
The cluster, called Cl0024+17, is actually thought to be two merging clusters, and some suggest that the ring was caused by their collision. To test the idea, John ZuHone, now at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and his colleagues simulated cluster collisions under varying conditions. They could not produce a ring unless the dark-matter particles had circular orbits.
Because such orbits are unlikely to occur in galaxy clusters, the results suggest that the ring report is questionable, says ZuHone.