The cluster CL0024+17, located in Pisces, is a galaxy cluster that is allowing astronomers to probe the distribution of dark matter in space. Dark matter does not reflect light and therefore cannot be seen. It is only detectable by the way its gravity affects the lights around it. Using gravitational lensing astronomers observe the distorted light around the dark matter and are able to tell where it is located within a cluster.
A dark matter ring found near the cluster’s center, by astronomers, provides some of the best evidence that dark matter actually exists.