Active Galaxies

Some galaxies are classified as active galaxies because of the extraordinary variability and evidence of strong interactions in their galactic nuclei. Some examples are Seyfert galaxies, B. L. Lacertae objects, and quasars.

Active Galactic Nuclei

Compared to ordinary galaxies, some galactic nuclei have extraordinary luminosities and are called active galaxies. The most dramatic examples are the quasars. Other active galactic nuclei have unusually bright, starlike nuclei, or have strong emission lines, or show high variability. Some have streams or jets coming from their cores. One class of active galaxies is the Seyfert galaxies.

Because of the enormous energies coming from rather small volumes, it is often suggested that these nuclei have massive black holes at their centers as a source of energy for the extraordinary luminosity. To date, the active galaxy M87 seems to be the best candidate.