Hubble composite image showing the ring of dark matter in the galaxy cluster Cl 0024+17. The ring-like structure is evident in the blue map of the clusters dark matter distribution. The map was derived from Hubble observations of how the gravity of the cluster Cl 0024+17 distorts the light of more distant galaxies, an optical illusion called gravitational lensing. Although astronomers cannot see dark matter, they can infer its existence by mapping the distorted shapes of the background galaxies. astronomers dont know what dark matter is made of, they hypothesize that it is a type of elementary particle that pervades the universe. The map is superimposed on a Hubble Advanced Camera for Surveys image of the cluster taken in November 2004.