Cosmology, Page 99: [Previous Page] [Next Page] [Class Home Page] Textbook pages 453 - 459

Unified Theory for Active Galaxies

The basic idea behind Unified Models of Active Galaxies is that all of the active galaxies which we observe have the same internal structure in their nucleus. All the differences that we see are caused by the angle of the system as seen in our direction.

When we see the system edge-on, the central region (the black hole, the central accretion disk, and much of the broadline region) is obscured. However we do see the molecular torus, and JETS! Objects: Seyfert 2s, Narrow Line Radio Galaxies When we see the system at a 45 degree angle, we start to see the central region. We now see both broad emission lines as well as narrow emission lines, and some direct, VERY HOT emission from the central accretion disk. Objects: Seyfert 1s, Broad Line Radio Galaxies, Type 1 Quasars Take a Quasar Tour.

For the VERY special case that we are seeing the system right down the center, we are looking right INTO the Jet! Because matter in the jet is moving at velocities close to the speed of light, that radiation has extremely high luminosities and can vary over short timescales. This jet emission is so strong, we hardly see the Broadline or Narrowline regions, so no emission lines. Objects: BL Lacertae (also called Blazars). Take the Active Galaxies Quiz!