BL Lacertae object

Last updated
BL Lacertae (center) is the prototype of BL Lacertae objects, with the surrounding host elliptical galaxy visible. The bright object at its left is a foreground star, while pixelated smudges are effects of data processing. BL Lacertae Pan-STARRS DR1.jpg
BL Lacertae (center) is the prototype of BL Lacertae objects, with the surrounding host elliptical galaxy visible. The bright object at its left is a foreground star, while pixelated smudges are effects of data processing.
The optical spectrum of the BL Lac object PG 1553+11 Fig1553.jpg
The optical spectrum of the BL Lac object PG 1553+11

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]

Contents

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.

Host galaxies

Centaurus A, the closest BL Lac object to the Milky Way. ESO Centaurus A LABOCA.jpg
Centaurus A, the closest BL Lac object to the Milky Way.

Soon after the discovery of this unusual class of objects it was noted that the sources were surrounded by a faint nebulosity. In the late 1970s the use of modern detectors (such as CCD) allowed observers to probe with better accuracy the nature of the nebulosity. 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.

Extensive surveys taken with the Hubble Space Telescope of 132 BL Lac objects comprising seven complete radio, X-ray, and optically selected samples in 2000 studied the morphologies of possible BL Lac host galaxies. 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. BL Lac objects are luminous enough that only one quarter (6/22) of the images taken with z > 0.5 were resolved because of relatively short exposure times. [6] A de Vaucouleurs profile [7] looks to be a significantly preferred brightness profile for 58 of the 72 resolved host galaxies at over ~99% confidence. The results of this survey conclude that there is an 8% limit to the number of disk systems in BL Lac objects and is therefore consistent with the assumption that all BL Lac host galaxies could be elliptical. These ellipticals are very luminous with a median absolute K-corrected magnitude of mag (rms dispersion). This is comparable to the brightest cluster galaxies. [6]

History

The BL Lac object H 0323+022 (z=0.147) imaged at ESO NTT (R filter). The host galaxy and close companions are visible. H0323bl2.gif
The BL Lac object H 0323+022 (z=0.147) imaged at ESO NTT (R filter). The host galaxy and close companions are visible.

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. [8]

Within a year others observed that the radio flux varied, and that light was polarized. Peter Albert Strittmatter proposed the class of object in 1972 and added four objects. By 1976 there were 30 known objects. [9]

In 2017, a very high energy neutrino was detected by the IceCube project apparently coming from BL Lac object TXS 0506+056. [10]

Related Research Articles

<span class="mw-page-title-main">Quasar</span> Active galactic nucleus containing a supermassive black hole

A quasar is an extremely luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Quasars are usually categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.

An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such excess, non-stellar emissions have been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an active galaxy. The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.

<span class="mw-page-title-main">3C 273</span> Brightest quasar from Earth located in the constellation Virgo

3C 273 is a quasar located at the center of a giant elliptical galaxy in the constellation of Virgo. It was the first quasar ever to be identified and is the visually brightest quasar in the sky as seen from Earth, with an apparent visual magnitude of 12.9. The derived distance to this object is 749 megaparsecs. The mass of its central supermassive black hole is approximately 886 million times the mass of the Sun.

<span class="mw-page-title-main">Seyfert galaxy</span> Class of active galaxies with very bright nuclei

Seyfert galaxies are one of the two largest groups of active galaxies, along with quasar host galaxies. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.

<span class="mw-page-title-main">Blazar</span> Very compact quasi-stellar radio source

A blazar is an active galactic nucleus (AGN) with a relativistic jet 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. 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. 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.

<span class="mw-page-title-main">BL Lacertae</span> Active galaxy in the constellation Lacerta

BL Lacertae or BL Lac is a highly variable, extragalactic active galactic nucleus. It was first discovered by Cuno Hoffmeister in 1929, but was originally thought to be an irregular variable star in the Milky Way galaxy and so was given a variable star designation. In 1968, the "star" was identified by John Schmitt at the David Dunlap Observatory as a bright, variable radio source. A faint trace of a host galaxy was also found. In 1974, Oke and Gunn measured the redshift of BL Lacertae as z = 0.07, corresponding to a recession velocity of 21,000 km/s with respect to the Milky Way. The redshift figure implies that the object lies at a distance of 900 million light years.

<span class="mw-page-title-main">OVV quasar</span> Type of highly variable quasar or subtype of blazar

An optically violent variable quasar is a type of highly variable quasar. It is a subtype of blazar that consists of a few rare, bright radio galaxies, whose visible light output can change by 50% in a day. OVV quasars have essentially become unified with highly polarized quasars (HPQ), core-dominated quasars (CDQ), and flat-spectrum radio quasars (FSRQ). Different terms are used but the term FSRQ is gaining popularity effectively making the other terms archaic.

<span class="mw-page-title-main">Low-ionization nuclear emission-line region</span> Type of galactic nucleus

A low-ionization nuclear emission-line region (LINER) is a type of galactic nucleus that is defined by its spectral line emission. The spectra typically include line emission from weakly ionized or neutral atoms, such as O, O+, N+, and S+. Conversely, the spectral line emission from strongly ionized atoms, such as O++, Ne++, and He+, is relatively weak. The class of galactic nuclei was first identified by Timothy Heckman in the third of a series of papers on the spectra of galactic nuclei that were published in 1980.

The Whole Earth Blazar Telescope (WEBT) is an international consortium of astronomers created in 1997, with the aim to study a particular category of Active Galactic Nuclei (AGN) called blazars, which are characterized by strong and fast brightness variability, on time scales down to hours or less.

<span class="mw-page-title-main">S5 0014+81</span> Black Hole in the constellation Cepheus

S5 0014+81 is a distant, compact, hyperluminous, broad-absorption-line quasar, or blazar, located near the high declination region of the constellation Cepheus, near the North Equatorial Pole.

The Parkes Catalogue of Radio Sources, also known as the Parkes Southern Radio Source Catalog, consists of 8264 astronomical radio sources, mostly south of declination +27. The catalogue was mostly compiled by John Bolton and his colleagues for 20 years. Both the Molonglo 408-MHz survey and the 80-MHz Culgoora measurements of Slee et al have contributed to the usefulness of the catalogue. For now, the catalogue only contains sources originally found in the Parkes 2700-MHz survey. The catalogue contains radio sources that have a frequency range of 80 - 22,000 MHz.

<span class="mw-page-title-main">AP Librae</span> Active galactic nucleus in the constellation Libra

AP Librae is a BL Lacertae object located at a distance of 700 million light years in the southern constellation of Libra. In the visual band it is one of the most active blazars known. AP Lib is surrounded by an extended source with a spectrum characteristic of a red-shifted giant elliptical galaxy. The derived visual magnitude of this region is 15.0, and it follows a radially decreasing brightness that is characteristic of an elliptical. Seven fainter galaxies are visible within an angular radius of 9′, suggesting it is the brightest member of a galactic cluster.

<span class="mw-page-title-main">PKS 2131-021</span> Quasar in the constellation Aquarius

PKS 2131-021 is quasar and a BL Lacerate object, producing an astrophysical jet. lt is located in the constellation Aquarius and classified as a blazar, a type of active galactic nucleus whose relativistic jet points in the direction towards Earth.

<span class="mw-page-title-main">PKS 0537-286</span> Quasar in the constellation Columba

PKS 0537-286, also known as QSO B0537-286, is a quasar located in the constellation Columba. With a redshift of 3.104, the object is located 11.4 billion light years away and belongs to the flat spectrum radio quasar blazar subclass (FSQR). It is one of the most luminous known high-redshift quasars.

<span class="mw-page-title-main">PKS 2126-158</span> Quasar in the constellation Capricornus

PKS 2126-158, also known as PKS 2126-15, is a quasar located in Capricornus. It has a redshift of 3.268000, which corresponds to the distance of 11.5 billion light years. It is classified as a gigahertz peaked-spectrum quasar (GPS) with a flat-spectrum radio source and a blazar, a type of active galaxy shooting an astrophysical jet towards Earth.

<span class="mw-page-title-main">PKS 0226-559</span>

PKS 0226-559 known as PMN J0228-5546 is a quasar located in the constellation Horologium. At the redshift of 2.464, the object is roughly 10.6 billion light-years from Earth.

<span class="mw-page-title-main">PKS 1144-379</span> Quasar in the constellation Centaurus

PKS 1144-379 also known as PKS B1144-379, is a quasar located in the constellation of Centaurus. At the redshift of 1.048, the object is located nearly 8 billion light-years from Earth.

<span class="mw-page-title-main">PKS 1402-012</span> Quasar in the constellation of Virgo

PKS 1402-012, also known as UM 632, is a quasar located in the constellation of Virgo. With a redshift of 2.51, the object is located 10.7 billion light-years from Earth.

<span class="mw-page-title-main">PKS 1402+044</span> Quasar in the constellation of Virgo

PKS 1402+044 is a quasar located in the constellation of Virgo. It has a redshift of 3.207, estimating the object to be located 11.3 billion light-years away from Earth.

<span class="mw-page-title-main">PKS 0805-07</span> Quasar in the constellation of Monoceros

PKS 0805-07 also known as PMN J0808-0751 and 4FGL J0808.2-0751, is a quasar located in the constellation of Monoceros. With a redshift of 1.83, light has taken at least 10 billion light-years to reach Earth.

References

  1. ↑ 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 .
  2. 1 2 Falomo, 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.
  3. ↑ 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.
  4. ↑ 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.
  5. ↑ Chiaberge, M.; Capetti, A.; Celotti, A. (2001). "The BL Lac heart of Centaurus A". Monthly Notices of the Royal Astronomical Society. 324 (4): L33–L37. arXiv: astro-ph/0105159 . Bibcode:2001MNRAS.324L..33C. doi: 10.1046/j.1365-8711.2001.04642.x .
  6. 1 2 Urry, Megan (2000). "The Hubble Space Telescope Survey of BL Lacertae Objects". The Astrophysical Journal. 523 (2): 816–829. arXiv: astro-ph/9911109 . Bibcode:2000ApJ...532..816U. doi:10.1086/308616.
  7. ↑ Sparke, L. S.; Gallagher, J. S. III (2007). Galaxies in the Universe: An Introduction. Cambridge University: Cambridge University Press. p. 244. ISBN   978-0-521-67186-6.
  8. ↑ Schmitt, John L. (May 1968). "BL Lac identified as a Radio Source". Nature. 218 (5142): 663. Bibcode:1968Natur.218..663S. doi: 10.1038/218663a0 .
  9. ↑ Stein, W. A.; O'Dell, S. L.; Strittmatter, P. A. (September 1976). "The BL Lacertae Objects" (PDF). Annual Review of Astronomy and Astrophysics. 14: 173–195. Bibcode:1976ARA&A..14..173S. doi:10.1146/annurev.aa.14.090176.001133.
  10. ↑ Overbye, Dennis (12 July 2018). "It Came From a Black Hole, and Landed in Antarctica". NY Times. Retrieved 2018-07-16.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.