BL Lac object

A BL Lac object is a quasar or other active galactic nucleus or active galaxy that shows substantial variation and some specific characteristics, showing rapid variation in radio, and showing polarization. They are thought to be AGNs with jets that are pointed at or near us. They are named for BL Lacertae, which was originally considered a variable star (thus given this variable star designation), and the progenitor of a variable-star type, but these were later determined to be AGNs. The term blazar may be considered a subtype of BL Lac object, but is also used virtually as a synonym. They are now among the AGN subtypes presumed explained by the unified model of AGNs.