active galactic nucleus
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active galactic nucleus(AGN) See active galaxy.
active galactic nucleus[¦ak·tiv gə‚lak·tik ′nü·klē·əs]
A central region of a galaxy, a light-year or less in diameter, where violent and apparently explosive behavior is observed which is manifested in many ways, including the high-velocity outflow of gas, strong nonthermal radio emission, intense and often polarized and highly variable radiation over a wide range of wavelength bands, and ejection of jets of relativistic material.