Seyfert galaxies are spiral-shaped galaxies characterized by an exceptionally bright nucleus that produce spectral line emission from highly ionized gas. Like the Milky Way, they consist of a central disk of stars with starry arms that extend outward and wrap around the disk like a pinwheel, but Seyfert galaxies display very faint arms and a very bright nucleus. The nuclei, in addition to emitting radiation in visible light wavelengths, also give off infrared radiation, radio waves, and X-rays. They contained very hot gases: hydrogen, ionized oxygen, nitrogen, neon, sulphur, iron, and argon. These gases are prone to explosions, which cause the nucleus to rotate much faster and more violently than the rest of the galaxy. Seyfert galaxies greatly outshine the other galaxies in a cluster. Some even approach the brightness of quasars, the brightest and most distant objects from Earth. The nuclei of Seyfert galaxies are also similar to quasars in that both types of objects emit radiation from all across the electromagnetic spectrum. This pattern has led some astronomers to theorize that the nuclei of Seyfert galaxies may be faint quasars. Another recent theory about Seyfert galaxies is that they are a stage of development through which all giant spirals pass. If this is true, our own Milky Way galaxy may spend 10 percent of its existence as a Seyfert galaxy.
Seyfert galaxies were named after Carl Keenan Seyfert, the astronomer who first identified the class in 1943.
