Introductory Astronomy: BL Lac Objects

BL Lac objects, like Seyferts, are galaxies without radio lobes but with extremely bright, tiny cores. However, BL Lac objects are the active cores of elliptical galaxies. These objects have no absorption nor emission lines in their cores. ALthough none have radio lobes, some have jets which are emitted directly from the active core.

It is thought that they are produced when we observe the active core of an elliptical galaxy almost directly through the central opening of the accretion disk. In other words, we are looking almost directly down the jet towards the central hole. This is why these objects appear so bright in radio light! Such relativistic jets have been clocked at about 48% of the speed of light in other objects!

BL Lac objects are much less common than Seyferts and therefore have been observed much less often. We do not have much detailed information about them.