Glossary term: Active Galactic Nucleus

Description: An active galactic nucleus (AGN) is a very luminous region at the center of a galaxy. It is thought to be powered by a supermassive black hole which accretes surrounding matter, forming an extremely hot accretion disk around it. AGNs have quite complex structures, with many different regions that emit light with different characteristics, and are often surrounded by a donut-shaped torus of dusty material. An AGN sometimes sends out jets of material in opposite directions. While many galaxies have a supermassive black hole in the center, not all are accreting matter and hence not all are AGN.

AGN is a general term that includes objects such as quasars, blazars, Seyfert galaxies, and radio galaxies. The different observational properties of these types of objects are thought to result in part from AGNs being viewed from different angles.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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