Seyfert galaxies

Seyfert galaxies are a class of galaxies with nuclei that produce spectral line emission from highly ionized gas, named after Carl Keenan Seyfert, the astronomer who first identified the class in 1943<ref name="seyfert1943>. They are a subclass of active galactic nuclei (AGN), and are thought to contain supermassive black holes.
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A specific class of galaxies which have active galactic nuclei. These can be spiral galaxies or barred spiral galaxies which have bright, compact galactic nuclei. The nuclei far outshine the spiral arms of the host galaxies and are far too bright to be composed only of stars. The electromagnetic radiation released by these Seyfert nuclei is not in the form of black body radiation, either, and hence cannot possibly be starlight. These observations have lead to the idea that there is something else, which is very energetic, in the nuclear region as well. The spectra of the nuclear regions contain spectral emission lines which suggest that hydrogen clouds are swirling around the active galactic nucleus at very high velocities. In many ways, Seyferts resemble quasars but are slightly less powerful and much closer to us. See also unified theory of active galaxies.