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Blazar in galaxy Markarian 501

Submitter: Albert van Duin
Description: A blazar is a very compact and highly variable energy source associated with a supermassive black hole at the center of a host galaxy. Blazars are among the most violent phenomena in the universe and are an important topic in extragalactic astronomy.

Blazars are members of a larger group of active galaxies, also termed active galactic nuclei (AGN). However, blazars are not a homogeneous group and can be divided into two: highly variable quasars, sometimes called Optically Violent Variable (OVV) quasars (these are a small subset of all quasars) and BL Lacertae objects ("BL Lac objects" or simply "BL Lacs"). A few rare objects may be "intermediate blazars" that appear to have a mixture of properties from both OVV quasars and BL Lac objects. The name "blazar" was originally coined in 1978 by astronomer Ed Spiegel to denote the combination of these two classes.

Blazars are AGN with a relativistic jet that is pointing in the general direction of the Earth. We observe "down" the jet, or nearly so, and this accounts for the rapid variability and compact features of both types of blazars. Many blazars have apparent superluminal features within the first few parsecs of their jets, probably due to relativistic shock fronts.

The generally accepted picture is that OVV quasars are intrinsically powerful radio galaxies while BL Lac objects are intrinsically weak radio galaxies. In both cases the host galaxies are giant ellipticals.

(From Wikipedia, the free encyclopedia)

This image is galaxy Markarian 501 (hosting a blazar) in the constellation of Hercules. The designation of the radio source is 1652+398. It is a single 5 minute exposure with my 20cm Astrograph and a modified Canon 40D digital camera from my back garden in Beilen on July 4, 2008. The galaxy is the fuzzy star in the middle of the picture.
Copyright: Albert van Duin
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