D galaxy

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The galaxy cluster Abell S0740 with dominant cD galaxy, recorded by the Hubble space telescope

A D galaxy (“D” for “ diffuse ”) is a special type of giant elliptical galaxy . It differs from an ordinary elliptical galaxy by its huge, diffuse halo .

The most important D galaxies can be found in the center of rich galaxy clusters, where they often appear individually or in pairs and reach enormous sizes with radii of up to 1 million light years . Such D galaxies are called cD galaxies (“c” denotes the luminosity class ).

The most famous example of a galaxy cluster with a central pair of cD galaxies is the relatively close Coma cluster with the two giant galaxies  NGC 4874 and  NGC 4884 . They are orbited by over 1000 individual star systems of normal size at intervals of up to around 20 mega parsecs , which, however, takes an enormous amount of time.

It is assumed that cD galaxies are formed by merging giant elliptical galaxies with other galaxies in the richly populated central area of ​​the clusters ( “galactic cannibalism” ). This is also indicated by the facts that many galaxies of this type have multiple nuclei and that almost all of them are powerful radio sources .

Individual evidence

  1. ↑ a b daviddarling.info: D galaxy , accessed on August 18, 2018
  2. ^ WW Morgan, DE Osterbrock: On the Classification of the Forms and the Stellar Content of Galaxies. In: The Astronomical Journal. 74, p. 515, doi : 10.1086 / 110828 .
  3. ^ CJ Conselice, JS Gallagher: Galaxy aggregates in the Coma cluster. In: Monthly Notices of the Royal Astronomical Society. 297, 1998, p. L34, doi : 10.1046 / j.1365-8711.1998.01717.x .
  4. ^ Hrant M. Tovmassian, Heinz Andernach: On the formation of cD galaxies and their parent clusters. In: Monthly Notices of the Royal Astronomical Society. 427, 2012, p. 2047, doi : 10.1111 / j.1365-2966.2012.22044.x .
  5. ↑ L. Tonry, John. (1987). Properties of cD Galaxies. Proceedings of the International Astronomical Union. 127. 89-96. 10.1007 / 978-94-009-3971-4_7.
  6. ↑ S. Giacintucci, T. Venturi, M. Murgia, D. Dallacasa, R. Athreya, S. Bardelli, P. Mazzotta, DJ Saikia: Radio morphology and spectral analysis of cD galaxies in rich and poor galaxy clusters. In: Astronomy & Astrophysics. 476, 2007, p. 99, doi : 10.1051 / 0004-6361: 20077918 .