XMM-Newton discovers part of the missing matter in the universe

The newly-detected bridge connecting Abell 222 and Abell 223 would be part of this missing baryonic matter. Matter in the Universe is distributed in a web-like structure, and clusters of galaxies are the dense nodes of this cosmic web [2]. For 10 years, astronomers suspected that the missing baryonic matter is hot gas at very low density permeating the filamentary structure of the cosmic web. Because of its low density, detecting this hot gas was a very challenging task. This discovery was made possible because of the very fortunate geometry of the two clusters. As seen from the Earth, the filament connecting the two clusters is aligned along our line-of-sight, so that the entire emission from the filament is concentrated in a small region of the sky, thereby making its detection possible. Previous observations, at a lower sensitivity level, only allowed astronomers to detect the clusters and some groups of galaxies, the dense knots of the web. The high-sensitivity level now achieved with in-depth XMM-Newton observations makes it possible to observe the connecting wires of the cosmic web. This discovery is a step toward understanding the distribution of the matter within the large-scale structure of the Universe.

[1] The team of astronomers includes N. Werner (SRON, Netherlands), A. Finoguenov, A. Simionescu, H. Böhringer (MPI, Germany), J. S. Kaastra (SRON and Utrecht University, Netherlands), J. P. Dietrich (ESO, Germany), J. Vink (Utrecht University, Netherlands).

[2] A movie with a flight through a cosmic web is available at http://www.mpa-garching.mpg.de/galform/data_vis/index.shtml#flying_filament.

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