Dark matter’s filamentary structure observed for the first time

Nature : Researchers have used gravitational lensing to infer the presence of a dark-matter filament connecting the galaxy clusters Abell 222 and Abell 223. They chose to look between the clusters because the filament that is presumed to connect them is particularly massive and oriented “so that most of its mass lies along the line of sight to Earth, enhancing the lensing effect,” said Jörg Dietrich, a cosmologist at the University Observatory Munich and one of the authors of the paper published yesterday in Nature. By examining both x rays from plasma in the filament and the distortion of the light traveling from the more than 40 000 background galaxies lying behind the filament, the researchers determined that the bulk of it must be composed of dark matter. Refining the technique could help astrophysicists understand the structure of the universe and shed light on what dark matter is made of.