For the first time, a team of astronomers has "observed" a filament of dark matter connecting two neighboring galaxy clusters. Dark matter is a type of matter that interacts only very weakly with light and itself. It's very nature is mysterious. Mapping the dark matter filament's gravity was the key to the breakthrough. The result is considered a crucial first step by scientists. It provides the first direct evidence that the universe is filled by a lacework of dark matter filaments, upon which the visible matter in the universe is distributed like small beads.
Jörg Dietrich of the physics department at the University of Michigan, together with his co-workers, examined gravitational lensing in the Abell 222 and 223 galaxy clusters. These clusters each have about 150 galaxies, are about 2.4 Gly (1 Gly being a gigalight-year, or 1 billion light-years) distant from Earth, and are separated by about 0.4 Gly. Earlier work by Dietrich's team using the 8.2 meter Subaru telescope on Mauna Kea, and the XMM-Newton x-ray space telescope discovered that these two clusters appear to be connected by a bridge of hot gas