Active Galactic Nuclei

A blazar seen looking almost straight down its jet, so its light is dominated by the rapidly-variable, featureless glow of the jet itself rather than by emission lines — one of the most extreme, fast-varying kinds of active nucleus.

A galactic nucleus whose spectrum is dominated by emission from weakly-ionized gas. LINERs are the most common type of active nucleus, though whether they are all powered by a black hole or partly by hot old stars is still debated.

A galaxy — usually a giant elliptical — that pours enormous energy into twin jets and lobes of radio-emitting plasma, launched by its central black hole and reaching far beyond the visible galaxy. Centaurus A is the nearest.

A spiral galaxy with a bright, compact active nucleus whose spectrum shows broad or narrow emission lines from gas swirling near the central black hole — a relatively low-luminosity active galactic nucleus in an otherwise normal-looking galaxy.

The framework that the many types of active galactic nucleus — Seyferts, quasars, radio galaxies, blazars — are largely the same underlying object, a supermassive black hole accreting through a disk and torus, seen from different angles and at different luminosities. A model that explains the types, rather than a type itself.