Quasars and Active Galaxies

How many different kinds of active galaxies are there?

AGNs can occur in any type or shape of galaxy—spiral, elliptical, or irregular. Depending on exactly how the energy radiates from the AGNs, they can have very different appearances. This has led to a wide variety of types of AGN, such as Seyfert Type 1 and Seyfert Type 2 galaxies, radio galaxies, BL Lacertae objects, blazars, and radioloud and radio-quiet quasars. Sometimes, to simplify matters, astronomers refer to very luminous AGNs of all types as simply “quasars” or “quasi-stellar objects” (QSOs). AGNs are sometimes not particularly luminous, emitting substantially less light than the rest of their host galaxy. In these cases, they are called “low-luminosity AGNs” and, again, may have many different characteristics.


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