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How are quasars related to active galactic nuclei?

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six quasar host galaxies — Quasar Six quasar host galaxies, as observed by the Hubble Space Telescope.
Shown are apparently normal, solitary galaxies (left), colliding galaxies (centre), and merging galaxies (right).

Quasars are a high-luminosity class of active galactic nuclei (AGN), which are small, energetic regions located at the centers of galaxies.12

The relationship between them is defined by their shared physical mechanism: both are powered by the accretion of matter onto a central supermassive black hole. While AGNs encompass a broader population of objects—including lower-luminosity Seyfert galaxies—quasars represent the most luminous variety within this group.132

The distinction between an active nucleus and a dormant one lies in the accretion rate; in a quasar, the black hole actively consumes matter at a high rate, generating immense radiation that can outshine the host galaxy itself. Astronomers believe that many galaxies currently harboring dormant black holes may have functioned as quasars in their early history. The intense energy output during this active phase, including radiation and particle jets, plays a critical role in the evolution of the host galaxy by influencing star formation and regulating the growth of the central black hole.134