Warm–hot intergalactic medium
The warm–hot intergalactic medium (WHIM) refers to a sparse, warm-to-hot (105 to 107 K) plasma that cosmologists believe to exist in the spaces between galaxies and to contain 40–50% of the baryons (that is, 'normal matter' which exists as plasma or as atoms and molecules, in contrast to dark matter) in the universe at the current epoch. Because of the high temperature of the medium, it is more readily observed from the ultraviolet and low energy X-ray emission. This was detected in the 0.4–0.6 keV energy band as of 2010 using the orbiting XMM-Newton observatory. This emission forms 12% ± 5% of the diffuse X-ray background radiation.
Within the WHIM, gas shocks are created as a result of active galactic nuclei, along with the gravitationally-driven processes of merging and accretion. Part of the gravitational energy supplied by these effects is converted into thermal emissions of the matter by collisionless shock heating.
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- Bykov, A. M.; Paerels, F. B. S.; Petrosian, V. (February 2008), "Equilibration Processes in the Warm-Hot Intergalactic Medium", Space Science Reviews 134 (1–4): 141–153, arXiv:0801.1008, Bibcode:2008SSRv..134..141B, doi:10.1007/s11214-008-9309-4
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- Gupta, Anjali; Galeazzi, M.; Ursino, E. (May 2010), "Detection and Characterization of the Warm-Hot Intergalactic Medium", Bulletin of the American Astronomical Society 41: 908, Bibcode:2010AAS...21631808G
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