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SAO Observers - Object: BL Lac

BL Lacertae objects (BL Lac for short) exhibit no absorption or emission lines but have a strong continuum stretching from radio through X-ray wavelengths. BL Lac is a galaxy that is the prototype of its class.

The name remains from an original mis-identification of BL Lac as a variable star. Only later was it realized that it was a distant galaxy with peculiar properties, but the name stuck to the class of objects exhibiting the same features. BL Lac objects, like Seyferts, are elliptical galaxies without radio lobes but with extremely bright, tiny cores. Although none have radio lobes, some have jets which are emitted directly from the active core. BL Lac objects are most likely produced when we view the active core of an elliptical galaxy almost directly through the central opening of the accretion disk. Hence we are viewing them almost directly along the line-of-sight of the jet towards the central blackhole.

Historically BL Lac has varied between m~13 and 15.5. (See the AAVSO Light Curve, below).

Coordinates, Finder Chart