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6. BLAZARS

Besides for radio galaxies (DRAGNs), Seyfert galaxies, and quasars, astronomers have found it convenient to invent another term, Blazars, to describe the most luminous and violent active galactic nuclei. Blazars are also called BL Lac objects, or Optically Violent Variables. They have the following distinguishing characteristics:

they tend to be 10 - 100 times brighter than quasars seen at comparable redshifts;
their spectra tend to be dominated by continuum, with weak or no emission lines; and
they tend to radiate most of their power in the gamma ray band of the electromagnetic spectrum.

The image above is The Gamma Ray Sky as observed by the Compton Gamma Ray observatory. The bright sources above and below the Milky Way are blazars. For example, the brightest one, at about 1 o'clock, is the blazar 3C279. (Astronomers don't always distinguish blazars from quasars.) Its brightness can increase or decrease by factors of four in a few days, as you can see below.

A gamma ray (upper) and X-ray (lower) flare in the blazar 3C279. Source

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Last modified November 10, 2000
Copyright by Richard McCray