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The optical spectrum of the BL Lac object PG 1553+11The BL Lac object H 0323+022 (z=0.147) imaged at ESO NTT (R filter). The host galaxy and close companions are visible.
A BL Lacertae object or BL Lac object is a type of active galactic nucleus (AGN) or a galaxy with such an AGN, named after its prototype, BL Lacertae. In contrast to other types of active galactic nuclei, BL Lacs are characterized by rapid and large-amplitude flux variability and significant optical polarization.[1] Because of these properties, the prototype of the class (BL Lac) was originally thought to be a variable star. When compared to the more luminous active nuclei (quasars) with strong emission lines, BL Lac objects have spectra dominated by a relatively featureless non-thermal emission continuum over the entire electromagnetic range.[2] This lack of spectral lines historically hindered identification of the nature and distance of such objects.[2]
In the unified scheme of radio-loud active galactic nuclei, the observed nuclear phenomenology of BL Lacs is interpreted as being due to the effects of the relativistic jet closely aligned to the line of sight of the observer. BL Lacs are thought to be intrinsically identical to low-power radio galaxies. These active nuclei appear to be hosted in massive elliptical galaxies. From the point of AGN classification, BL Lacs are a blazar subtype. 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. This includes BL Lacs as well as optically violent variable (OVV) quasars, however in general practice, "Blazar" and "BL Lac Object" are often used interchangeably. OVV quasars are generally more luminous and have stronger emission lines than BL Lac objects.[4]
Some examples of BL Lac objects are BL Lacertae itself, OJ 287, AP Librae, PKS 2155-304, PKS 0521-365, Markarian 421, 3C 371, W Comae Berenices, ON 325 and Markarian 501.
^Padovani, Paolo; Giommi, Paolo (15 December 1995). "A Sample-Oriented Catalogue of BL Lacertae Objects". Monthly Notices of the Royal Astronomical Society. 277 (4): 1477–1490. arXiv:astro-ph/9511065v1. Bibcode:1995MNRAS.277.1477P. doi:10.1093/mnras/277.4.1477.
^ abFalomo, Renato (2014). "An Optical View of BL Lacertae Objects". The Astronomy and Astrophysics Review. 22: 44. arXiv:1407.7615. Bibcode:2014A&ARv..22...73F. doi:10.1007/s00159-014-0073-z.
^Marscher, A. P.; et al. (24 April 2008). "The inner jet of an active galactic nucleus as revealed by a radio-to-gamma-ray outburst" (PDF). Nature. 452 (7190): 966–969. Bibcode:2008Natur.452..966M. doi:10.1038/nature06895. hdl:2027.42/62749. PMID 18432239.
^Urry, Megan (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.
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BLLacertae or BL Lac is a highly variable, extragalactic active galactic nucleus (AGN or active galaxy). It was first discovered by Cuno Hoffmeister...
a BLLacertaeobject (of lower luminosity than its surrounds) seen from a relatively large angle. Flux variations, characteristic of the BLLacertae objects...
BL Lac may refer to: BLLacertae, an active galaxy, prototype of the BLLacertaeobjectsBLLacertaeobject, a type of active galaxy, based on the prototype...
(though still too faint to see with the naked eye); and PKS 2155-304, a BLLacertaeobject that is one of the optically brightest blazars in the sky. Pisces...
class of galaxy: BLLacertae-type objects. This terminology was soon shortened to "BLLacertaeobject", "BL Lac object" or simply "BL Lac". (The latter...
stars. It also contains the prototypic blazar BLLacertae. Lacerta contains no Messier objects. Alpha Lacertae is a blue-white hued main-sequence star of...
AP Librae is a BLLacertaeobject located at a distance of 700 million light years in the southern constellation of Libra. In the visual band it is one...
; Dressel, Linda L.; Harms, Richard J. (1998). "M87: A Misaligned BLLacertaeObject?". The Astrophysical Journal. 493 (2): L83–L86. arXiv:astro-ph/9711241...
blazar located in the constellation Ursa Major. The object is an active galaxy and a BLLacertaeobject, and is a strong source of gamma rays. It is about...
OJ 287 is a BL Lac object 5 billion light-years from Earth that has produced quasi-periodic optical outbursts going back approximately 120 years, as first...
Bibcode:1968ApJ...151L..79U. doi:10.1086/180147. Wikisky image of 3C 371 New X-ray Jet in Nearby BLLacertaeObject 3C371 (Brandeis University Radio Astronomy)...
rays. It is a blazar or BL Lac object, which is an active galactic nucleus with a jet that is shooting towards the Earth. The object has a redshift of z =...
was originally designated a variable star and later found to be a BLLacertaeobject. As of 2009, it had the most intense gamma ray spectrum of the sixty...
Kolb, J.; Marchetti, E.; Tordo, S. (April 1, 2011). "The jet of the BLLacertaeobject PKS 2201+044: MAD near-IR adaptive optics observations and comparison...
Magellanic Cloud. Moreover, satellite galaxies are not the only astronomical objects that are gravitationally bound to larger host galaxies (see globular clusters)...
of Bright Quasars and BLLacertaeObjects Kitt Peak Quasar List (1975) VII/11 Revised and Updated Catalog of Quasi-stellar Objects (1993) VII/158 Portals:...
"something that none of us had even thought would be possible." WATGs are rare objects that are formed when jets of electrons from black holes, usually seen to...
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