Warm–hot intergalactic medium

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Computer simulation showing the distribution of warm-hot intergalactic gas

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%[1] 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.[2] It can be described as a web of hot, diffuse gas. Much of what is known about the warm-hot intergalactic medium comes from computer simulations of the cosmos.[3] The WHIM is expected to form a filamentary structure of tenuous, highly ionized baryons with a density of 1−10 particles per cubic meter.[4] 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.[1]

Because of the high temperature of the medium, the expectation is that it is most easily observed from the absorption or emission of ultraviolet and low energy X-ray radiation. To locate the WHIM, researchers examined X-ray observations of a rapidly growing super massive black hole known as an active galactic nucleus, or AGN. Oxygen atoms in the WHIM were seen to absorb X-rays passing through the medium.[5] In May 2010 a giant reservoir of WHIM was detected by the Chandra X-ray Observatory lying along the wall shaped structure of galaxies (Sculptor Wall) some 400 million light-years from Earth.[5][6]

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References[edit]

  1. ^ a b 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:0801.1008Freely accessible, Bibcode:2008SSRv..134..141B, doi:10.1007/s11214-008-9309-4 
  2. ^ Reimers, D. (2002), "Baryons in the diffuse intergalactic medium", Space Science Reviews, 100 (1/4): 89, Bibcode:2002SSRv..100...89R, doi:10.1023/A:1015861926654 
  3. ^ Ryden, Barbara; Pogge, Richard (June 2016), Interstellar and Intergalactic Medium, Ohio State Graduate Astrophysics Series, The Ohio State University, pp. 240−244, ISBN 978-1-914602-02-7 
  4. ^ Nicastro, Fabrizio; et al. (January 2008). "Missing Baryons and the Warm-Hot Intergalactic Medium". Science. 319 (5859): 55. arXiv:0712.2375Freely accessible. Bibcode:2008Sci...319...55N. doi:10.1126/science.1151400. 
  5. ^ a b "Huge Chunk of Universe's Missing Matter Found". Space.com. Retrieved 2016-12-05. 
  6. ^ "Last "Missing" Normal Matter Is Found - Sky & Telescope". 14 May 2010.