D galaxy
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
- ↑ a b daviddarling.info: D galaxy , accessed on August 18, 2018
- ^ 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 .
- ^ 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 .
- ^ 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 .
- ↑ 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.
- ↑ 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 .