An extremely bright, starlike object characterized by rapid changes in luminosity and a flat spectrum. Originally thought to be ordinary irregular variable stars, their spectral properties now lead astronomers to consider blazars as a class of active galactic nuclei. Blazars emit radiation over a very wide range of frequencies, from radio to gamma rays, with their jets pointed at the observer. This orientation accounts for their peculiar properties, specifically the variability and intensity of their brightness, and it also distinguishes blazars from another class of active galactic nucleus, quasars.
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