Blazar
Blazars are highly variable sources, often undergoing rapid and dramatic fluctuations in brightness on short timescales (hours to days).
The blazar category includes BL Lac objects and optically violently variable (OVV) quasars.
Blazar research includes investigation of the properties of accretion disks and jets, the central supermassive black holes and surrounding host galaxies, and the emission of high-energy photons, cosmic rays, and neutrinos.
[4][5][6] Blazars, like all active galactic nuclei (AGN), are thought to be powered by material falling into a supermassive black hole in the core of the host galaxy.
Gas, dust and the occasional star are captured and spiral into this central black hole, creating a hot accretion disk which generates enormous amounts of energy in the form of photons, electrons, positrons and other elementary particles.
There is also a larger opaque toroid extending several parsecs from the black hole, containing a hot gas with embedded regions of higher density.
Perpendicular to the accretion disk, a pair of relativistic jets carries highly energetic plasma away from the AGN.
The jet is collimated by a combination of intense magnetic fields and powerful winds from the accretion disk and toroid.
All of these regions can produce a variety of observed energy, mostly in the form of a nonthermal spectrum ranging from very low-frequency radio to extremely energetic gamma rays, with a high polarization (typically a few percent) at some frequencies.
These blazars, like genuine irregular variable stars, changed in brightness on periods of days or years, but with no pattern.
In 1968, a similar connection was made between the "variable star" BL Lacertae and a powerful radio source VRO 42.22.01.
[7] BL Lacertae shows many of the characteristics of quasars, but the optical spectrum was devoid of the spectral lines used to determine redshift.
In 1972 a few variable optical and radio sources were grouped together and proposed as a new class of galaxy: BL Lacertae-type objects.
[8][9] Blazars are thought to be active galactic nuclei, with relativistic jets oriented close to the line of sight with the observer.
