Intergalactic medium

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As intergalactic medium (English: intergalactic medium - IGM , also intergalactic gas ) is called hydrogen - gas , which is not bound to individual galaxies , but fills the space between them. It consists mainly of ionized hydrogen gas / plasma (HII); neutral hydrogen (H or HI) only makes up about a millionth of the entire medium.

The IGM should not be confused with the interstellar medium that is found between the stars within a galaxy. However, the boundaries between intergalactic and interstellar medium are fluid.

Classification

Warm-Hot Intergalactic Medium (WHIM)

WHIM is the name given to the medium between individual galaxies. The Lyman-Alpha-Forest in the optical spectra of distant quasars or other active galaxy nuclei is evaluated as an indication of the intergalactic medium . The absorption lines are generated by the neutral hydrogen that collects in the cosmic filaments .

In 2001, signs of this Gunn-Peterson effect were discovered in a quasar . However, this gas would have to show up in the background radiation in the X-ray or possibly also in the gamma range . Observations from the X-ray satellite Chandra show, however, that at least 75% of the background radiation in the hard X-ray range can be resolved into quasars, Seyfert galaxies or active galaxy nuclei. This leaves little room for a general intergalactic medium.

Intracluster Medium (ICM)

The medium within galaxy clusters (clusters) is called intracluster medium . Because of its relatively high temperature of 10 7 to 10 8 K , the ICM can be observed through its X-ray radiation, which is produced as bremsstrahlung . The gas is completely ionized and makes up about 15% of the total mass of a heap. It is the dominant baryonic component in galaxy clusters.

Individual evidence

  1. ↑ Philip Richter: An overview of the field of work of astrophysics II at the University of Potsdam
  2. ↑ A. Unsöld and B. Baschek: The new cosmos p. 474 (7A)
  3. ↑ Peter Schneider : Introduction to Extragalactic Astronomy and Cosmology . Springer, December 2005, ISBN 3-540-25832-9