Concept information
Preferred term
Active galactic nuclei
Definition
- A central region of an active galaxy, which is a light-year or less in diameter and has an abnormally high luminosity. The nucleus emits high energy radiation (gamma rays, X-rays, ultraviolet) and shows variability over various time-scales, sometimes very short (hours to weeks). Emission line spectra reveal high velocity motions up to 10^4 km s^-1. AGNs are divided into two main types. Type I refers to an AGN whose nucleus is visible (the spectra has both narrow and broad emission lines), while in type II AGN, the broad line region (BLR) is obscured and the lines are very narrow. This may be due either to the viewing angle or some intrinsic difference in structure. (en)
Broader concept
- Active galaxies (en)
- Galaxy nuclei (en)
- High energy astrophysics (en)
Narrower concepts
- Blazars (en)
- High-luminosity active galactic nuclei (en)
- Low-luminosity active galactic nuclei (en)
- Quasars (en)
- Radio active galactic nuclei (en)
- Radio cores (en)
- Radio hot spots (en)
- Radio jets (en)
- Radio lobes (en)
- Radio plumes (en)
- Relativistic disks (en)
- X-ray active galactic nuclei (en)
Entry terms
- AGN (en)
- AGNs (en)
Contributor
Editorial note
URI
http://astrothesaurus.org/uat/16
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