Seyfert Galaxies
These galaxies show an intense, point-like nucleus. Their Hubble types are dominated by early-type spirals (Sa and Sb, both barred and non-barred) and S0 systems. Spectra of Seyferts show normal lines from typical stars.

However, these galaxies really stand out, showing strong emission lines of Hydrogen and Helium in the nucleus. Moreover, these emission lines are incredibly broad, indicating velocities of thousands of km/s. Something quite unusual is occurring in these galaxies! Click here for a Seyfert 1 spectrum, and here for a Seyfert 2 spectrum.

Radio Galaxies
The image of Cygnus A shown below was taken at radio wavelengths. It shows the common morphology of radio 'lobed' radio galaxies. Click here to see its optical counterpart.

A compact radio source called the "core" coincides with the galactic nucleus. Most of the radio emission does not come from the well-collimated "jets", but from the broader "lobes" found around the jet paths. The plasma in the lobes is believed to have been supplied by the jets over millions of years. In the more powerful radio galaxies, there are usually small, bright radio "hot spots" near the boundaries of each lobe. These hot spots are thought to be where strong shocks form near the ends of the supersonic jet outflow.

What causes the radio emission?
The origin of the radio emission from radio galaxies is non-thermal, synchrotron emission. This light is produced by "relativistic" electrons, moving near the speed of light, spiraling around lines of magnetic force.