Astronomers have discovered a filament of gas connecting four galaxy clusters. At temperatures of more than 10 million degrees, the filament contains about 10 times the mass of the Milky Way and connects two galaxy clusters at one end with two at the other. All four are part of the Shapley Supercluster, a group of more than 8,000 galaxies that forms one of the most massive known cosmic structures. The filament stretches for 23 million light years and could contain as yet undetected matter, such as dark matter, which makes up 27% of the Universe, and to a lesser extent, normal matter, which represents 15%. Theoretical models suggest that this elusive matter could exist in long chains of gas—known as filaments—connecting dense pockets of space. Astronomers identified the filament by combining observations from the European Space Agency’s X-ray space telescope with readings from a counterpart operated by the Japan Aerospace Exploration Agency (ESA and Astronomy and Astrophysics, June 19).
