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Seyfert galaxy

From Simple English Wikipedia, the free encyclopedia
The Circinus Galaxy, a Type II Seyfert galaxy
A diagram of an active galactic nucleus. The central black hole is surrounded by an accretion disc, which is surrounded by a torus. The broad line region and narrow line emission region are shown, as well as jets coming out of the nucleus

Seyfert galaxies are a type of galaxy. They are named after Carl Seyfert who first described them in 1943.[1]

These galaxies are one of the two main types of active galaxies. The other large group are quasars. Seyfert galaxies have quasar-like nuclei: they are very distant luminous sources of electromagnetic radiation. Their very high surface brightness has spectra with strong, high-ionisation emission lines.[2] However, unlike quasars, their host galaxies are clearly visible.[3]

Seyfert galaxies are about 10% of all galaxies,[4] and are some of the most intensely studied objects in astronomy. They are thought to be powered by the same phenomena as quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission lines and absorption lines are the best way to analyse the surrounding material.[5]

Seen in visible light, most Seyfert galaxies look like normal spiral galaxies. However, when studied under other wavelengths, it becomes clear that the luminosity of their cores is as big as the luminosity of whole galaxies the size of the Milky Way.[6]

Examples[change | change source]

Seyfert galaxy Messier 51
Seyfert galaxy Messier 87
Seyfert galaxy Centaurus A

Here are some notable examples of Seyfert galaxies:

References[change | change source]

  1. Seyfert, Carl K. 1943. Nuclear emission in spiral nebulae. The Astrophysical Journal. 97: 28–40. [1]
  2. Peterson, Bradley M. 1997. An introduction to active galactic nuclei. Cambridge University Press. ISBN 978-0-521-47911-0 [2]
  3. Petrov G.T. (ed) 2004. Active galaxy nuclei. Bulgarian Academy of Sciences/Institute of Astronomy [3].
  4. Maiolino R. & Rieke G.H. 1995. Low-luminosity and obscured Seyfert nuclei in nearby galaxies. The Astrophysical Journal. 454: 95–105. [4]
  5. Davidsen, Arthur F. 1993. Far-ultraviolet astronomy on the Astro-1 space shuttle mission. Science 259 (5093): 327–334. [5]
  6. Soper D.E. Seyfert galaxies. University of Oregon.
  7. Scalzi, John (2003). The Rough Guide to the Universe. Rough Guides. pp. 250. ISBN 1-85828-939-4.