Two distinct classes were identified by Ed Khachikian and Daniel Weedman on the basis of their emission lines. Class 1 Seyferts, such as NGC 5548, show broadening only of their hydrogen lines – those that can be associated with the highest gas densities. Class 2 Seyferts, such as NGC 1068 (the brightest known Seyfert), show broadening of all their lines. In both cases, the spectrum points to the presence of large amounts of very hot, fast-moving gas close to the galactic center that is being prevented from escaping by a large central mass.
Variations in brightness over periods of a few months exhibited by some Seyferts, for example NGC 4151, show that the bulk of the radiation comes from regions at most a few light-months across. Although the visual luminosity of Seyferts is not unusual for spirals, their total luminosity, including radio wave, X-ray, and, most significantly, infrared emission, is roughly 100 times normal. Taken as a whole, Seyferts display many of the properties of quasars and almost certainly produce the bulk of their energy output in the same way – through the gravitational influence of a supermassive black hole at the heart of an active galactic nucleus.
Related category GALAXIES
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