BL Lacertae object

In contrast to other types of active galactic nuclei, BL Lacs are characterized by rapid and large-amplitude flux variability and significant optical polarization.

All known BL Lacs are associated with core dominated radio sources, many of them exhibiting apparent superluminal motion.

[3] The blazar category encompasses all quasars oriented with the relativistic jet directed at the observer giving a unique radio emission spectrum.

First images of the BL Lac object PKS 0548-322 by Michael John Disney in 1974 in various filters found it to be composed by a giant elliptical galaxy with a bright nucleus.

The data concluded that in two-thirds of the BLL images taken, host galaxies are detected, including in nearly all with redshift z < 0.5.

[6] John L. Schmitt first noticed the peculiar nature of BL Lac in 1968 when he matched it with a radio object, VRO 42.22.01.

[9] In 2017, a very high energy neutrino was detected by the IceCube project apparently coming from BL Lac object TXS 0506+056.