The center of a galaxy, usually small, very bright, and containing a high density of stars and other objects.♦ An active galactic nucleus is a nucleus that emits more radiation than can be explained in terms of stars alone. Blazars and quasars are thought to be active galactic nuclei; the nuclei of Seyfert galaxies are also active, and are thought to contain an extremely massive black hole.
Active galactic nucleus – Wikipedia
What are Active Galactic Nuclei? – Universe Today
Galactic Nuclei | COSMOS
Active Galactic Nuclei | COSMOS
Resolved structure of a galactic active nucleus – Resonance Science
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