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Seyfert galaxy
Seyfert galaxy A type of galaxy with a small, bright nucleus which shows broad, strong emission lines in its spectrum. The first galaxies of this type were described in 1943 by C. K.Seyfert. Nearly all known Seyfert galaxies are spirals or barred spirals, and Seyfert-type activity probably occurs in a small percentage of all spiral galaxies. Seyfert galaxies are classified according to the relative widths of the emission lines in their spectra. Type 1 Seyferts (such as NGC 5548) have broad emission lines of hydrogen but narrow forbidden lines of heavier elements. In Type 2 Seyferts (such as NGC 1068) the hydrogen lines and forbidden lines both have the same width, which is broader than the forbidden lines in Type 1 Seyferts but not as broad as the latter's hydrogen lines. Seyferts have active galactic nuclei that produce strong radiation, probably from an accretion disk around a massive black hole. The radiation excites gas around the central regions, giving rise to the observed emission lines. Seyferts are lower-luminosity examples of quasar activity.
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"Seyfert galaxy." A Dictionary of Astronomy. 1997. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "Seyfert galaxy." A Dictionary of Astronomy. 1997. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O80-Seyfertgalaxy.html "Seyfert galaxy." A Dictionary of Astronomy. 1997. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-Seyfertgalaxy.html |
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Seyfert galaxy
Seyfert galaxy Class of galaxies that have extremely bright, compact nuclei and whose spectra show strong emission lines. Most are spiral galaxies. About 1% of all galaxies are Seyferts. They emit strongly at ultraviolet and infrared wavelengths, and exhibit a degree of short-term variability. Sezession Radical movement (formed 1897) of young Austrian artists who organized their own exhibitions in defiance of the traditional organizations and aligned themselves with progressive European contemporaries. The first president was Gustav Klimt. Other members included Oskar Kokoschka and, later, Egon Schiele.
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Cite this article
"Seyfert galaxy." World Encyclopedia. 2005. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "Seyfert galaxy." World Encyclopedia. 2005. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O142-Seyfertgalaxy.html "Seyfert galaxy." World Encyclopedia. 2005. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-Seyfertgalaxy.html |
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