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Blazar

Not to be confused with Blazer or Blazor.
The elliptical galaxy M87 emitting a relativistic jet, as seen by the Hubble Space Telescope. An active galaxy is classified as a blazar when its jet is pointing close to the line of sight. In the case of M87, because the angle between the jet and the line of sight is not small, its nucleus is not classified as a blazar, but rather as radio galaxy.

A blazar is an active galactic nucleus (AGN) with a relativistic jet (a jet composed of ionized matter traveling at nearly the speed of light) directed very nearly towards an observer. Relativistic beaming of electromagnetic radiation from the jet makes blazars appear much brighter than they would be if the jet were pointed in a direction away from Earth.[1] Blazars are powerful sources of emission across the electromagnetic spectrum and are observed to be sources of high-energy gamma ray photons. Blazars are highly variable sources, often undergoing rapid and dramatic fluctuations in brightness on short timescales (hours to days). Some blazar jets appear to exhibit superluminal motion, another consequence of material in the jet traveling toward the observer at nearly the speed of light.

The blazar category includes BL Lac objects and optically violently variable (OVV) quasars. The generally accepted theory is that BL Lac objects are intrinsically low-power radio galaxies while OVV quasars are intrinsically powerful radio-loud quasars. The name "blazar" was coined in 1978 by astronomer Edward Spiegel to denote the combination of these two classes.[2]

In visible-wavelength images, most blazars appear compact and pointlike, but high-resolution images reveal that they are located at the centers of elliptical galaxies.[3]

Blazars are important topics of research in astronomy and high-energy astrophysics. 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.

In July 2018, the IceCube Neutrino Observatory team traced a neutrino that hit its Antarctica-based detector in September 2017 to its point of origin in a blazar 3.7 billion light-years away. This was the first time that a neutrino detector was used to locate an object in space.[4][5][6]

  1. ^ Urry, C. M.; Padovani, P. (1995). "Unified Schemes for Radio-Loud Active Galactic Nuclei". Publications of the Astronomical Society of the Pacific. 107: 803. arXiv:astro-ph/9506063. Bibcode:1995PASP..107..803U. doi:10.1086/133630. S2CID 17198955.
  2. ^ Kellermann, Kenneth (2 October 1992). "Variability of Blazars". Science. 258 (5079): 145–146. doi:10.1126/science.258.5079.145-a. PMID 17835899.
  3. ^ Urry, C. M.; Scarpa, R.; O'Dowd, M.; Falomo, R.; Pesce, J. E.; Treves, A. (2000). "The Hubble Space Telescope Survey of BL Lacertae Objects. II. Host Galaxies". The Astrophysical Journal. 532 (2): 816. arXiv:astro-ph/9911109. Bibcode:2000ApJ...532..816U. doi:10.1086/308616. S2CID 17721022.
  4. ^ Overbye, Dennis (12 July 2018). "It Came From a Black Hole, and Landed in Antarctica - For the first time, astronomers followed cosmic neutrinos into the fire-spitting heart of a supermassive blazar". The New York Times. Retrieved 13 July 2018.
  5. ^ "Neutrino that struck Antarctica traced to galaxy 3.7bn light years away". The Guardian. 12 July 2018. Retrieved 12 July 2018.
  6. ^ "Source of cosmic 'ghost' particle revealed". BBC. 12 July 2018. Retrieved 12 July 2018.[permanent dead link]

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