Active galaxies emit abnormally large amounts of energy from their central nuclei. Some active galaxies eject long jets of gas from their nuclei. The energy source for an active galaxy is a central supermassive black hole. Active galaxies emit abnormally large amounts of energy from their central nuclei. Intensity of the light peaks at visible wavelengths.
Light is distributed throughout the galaxy.
Intensity of the light peaks at radio wavelengths. The nucleus is highly luminous. The spectra of Seyfert galaxies are characterized by emission lines from highly ionized gas. Within the nuclei of Seyfert galaxies, then, there exists very hot gas which is swirling around very rapidly. The luminosity of the nucleus of a Seyfert galaxy can vary wildly on timescales of only a month.