A member of an important class of → active galaxies
which are characterized by the presence
of an intensely bright nucleus in the optical wavelengths (109-1012Lsun) displaying emission spectral lines. The presence of these emission features,
which are not seen in the spectra of normal galaxies,
indicates a very high degree of ionization. Moreover, the nucleus
radiates → non-thermal → continuum emission
extending over the whole electromagnetic
spectrum. It is thought that a → massive black hole
in the nucleus of a galaxy accretes gas (→ accretion) from
its surrounding environment to power Seyfert galaxies. These galaxies
are divided into
two types according to the width of their spectral lines. Type 1 Seyfert (Sy 1) galaxies
have very broad emission lines (103- 104 km s-1), while
Type 2 Seyferts (Sy 2) show relatively narrow lines (several hundred km s-1).
These spectral differences may be the result of viewing the nucleus from different
angles. A Type 2 Seyfert galaxy may be a mostly edge-on view of matter spiraling in toward
the supermassive black hole, whereas a Type 1 Seyfert provides a more pole-on
view, allowing us to see the more turbulent region around the black hole.
See also: Named after Carl Keenan Seyfert (1911-1960), the American astronomer who first identified
this type of galaxies in 1943; → galaxy.
