|BL Lac object|
|an extremely compact violently variable form of active galaxy|
|[C20: named after BL Lacertae, first identified example found in the constellation Lacerta and originally thought to be a variable star]|
|BL Lac object (bē'ěl' läk') Pronunciation Key
A distant radio galaxy with an intensely bright active galactic nucleus that emits a jet of material directly toward the Earth. BL Lac objects may be a class of blazar, though there is evidence that they are an optical effect caused by gravitational lensing of some other bright object by an intervening galaxy. Also known as BL Lacertae objects.