Active Galactic Nuclei
From Slackerpedia Galactica
Active galactic nuclei refer to galaxies with some kind of anomalous (i.e. non-stellar) emission in their centers. The activity is usually ascribed to the presence of a supermassive black hole, having millions or billions of times the mass of Sun. "Active Galactic Nuclei" is a generic term for this phenomenon; other, more specific terms like Seyfert galaxy or quasar refer to specific manifestations of AGNs. For example, Seyfert Galaxies are spiral galaxies with bright, point-like nuclei; quasars are AGN oriented along our line of sight such that we can see directly into the nucleus; blazars are quasars whose jets are pointed right at us.
The energy source for AGN is a supermassive black hole at the center of the galaxy. This black hole accretes all the gas, dust, and even whole stars at the centers of these galaxies. In the process, lots of energy gets released, making these objects shine very brightly. Because the accretion process is so energetic, AGN radiate at nearly all wavelengths of light, from radio waves to gamma rays.
