| definition |
A member of an important class of active galaxies which are characterized by the presence
of an intensely bright nucleus in the optical wavelengths (10^9-10^12 L_sun) 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 (10^3 - 10^4 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.
|
|
