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 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 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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A galaxy in which a small, bright centre is caused by hot gas moving at high speed around a massive central object, possibly a black hole. Almost all Seyferts are spiral galaxies. They seem to be closely related to quasars, but are about 100 times fainter. They are named after their discoverer, US astronomer Carl Seyfert.
- superimposed ice
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- superior
- superior conjunction
- superior planet
- Superior-type granular iron formation
- SuperJANET
- superlattice
- superluminal velocity
- Supermalloy
- superman
- supermassive black hole
- supermassive star
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- supermembrane theory
- Supermendur
- supernatant
- supernatant liquid
- supernormal profit
- supernormal stimulus
- supernova
- Supernova 1987A
- supernova remnant