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active galactic nucleus (AGN) |
 | | AGN are found at the heart of active galaxies, including quasars, Seyfert galaxies, blazars, and radio galaxies. |
 | | Since a fl hole, by definition, emits nothing, the radiation from an AGN is believed to come from material heated to several million degrees in an accretion disk before tumbling into the fl hole or, in some cases, being shot away in twin jets along the central engine’s spin axis. |
 | | Within each is a broad range of luminosity, from AGN so weak that they are barely detectable against the light from the central stars of their host galaxy to quasars that are more than 100 times brighter than all the stars in their hosts put together. |
| www.daviddarling.info /encyclopedia/A/AGN.html (738 words) |
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