Active galactic nucleus

Hubble Space Telescope image of a 5000-light-year-long (1.5-kiloparsec-long) jet being ejected from the active nucleus of the active galaxy M87, a radio galaxy. The blue synchrotron radiation of the jet contrasts with the yellow starlight from the host galaxy.

An active galactic nucleus (AGN) is a compact region at the centre of a galaxy. This central region radiates huge luminosity over the electromagnetic spectrum. The radiation from an AGN is thought to be caused by mass dragged in by the gravitational pull of a supermassive black hole at the centre of the host galaxy.

This electromagnetic radiation is observed in the radio, microwaves, infrared, optical, ultra-violet, X-ray and gamma ray wavebands.

A galaxy hosting an AGN is called an active galaxy. AGN are the most luminous and persistent sources of electromagnetic radiation in the universe. They can be used to discover distant objects. All theories about the cosmos have to account for AGNs. They are one of the basic facts about the universe.

So-called relativistic jets are extremely powerful jets of plasma which come from some AGNs, notably radio galaxies and quasars.^[1] Their lengths can reach several thousand or even hundreds of thousands of light years.^[2]^[3]

Active Galactic Nucleus Media

Quasar 3C 273 observed by the Hubble Space Telescope. The relativistic jet of 3C 273 appears to the left of the bright quasar, and the four straight lines pointing outward from the central source are diffraction spikes caused by the telescope optics.
UGC 6093 is classified as an active galaxy, which means that it hosts an active galactic nucleus.
Unified model of AGN adapted from Urry & Padovani (1995). The thick arrows represent different viewing angles, and the observed object which results from them. Note the asymmetry of the diagram; this is to demonstrate the two different possibilities of radio loud/quiet and is not representative of a single object.

References

↑ Wehrle A.E.; et al. (2009). "What is the structure of relativistic jets in AGN on scales of light days?" (PDF). {{cite journal}}: Cite journal requires |journal= (help)
↑ Biretta J. 1999. Hubble detects faster-than-llight motion in Galaxy M87 (http://www.stsci.edu/ftp/science/m87/m87.html)
↑ Yale University - Office of Public Affairs 2006. Evidence for ultra-energetic particles in jet from black hole (https://web.archive.org/web/20080513034113/http://www.yale.edu/opa/newsr/06-06-20-01.all.html)

[1] Wehrle A.E.; et al. (2009). "What is the structure of relativistic jets in AGN on scales of light days?" (PDF). {{cite journal}}: Cite journal requires |journal= (help)

[2] Biretta J. 1999. Hubble detects faster-than-llight motion in Galaxy M87 (http://www.stsci.edu/ftp/science/m87/m87.html)

[3] Yale University - Office of Public Affairs 2006. Evidence for ultra-energetic particles in jet from black hole (https://web.archive.org/web/20080513034113/http://www.yale.edu/opa/newsr/06-06-20-01.all.html)

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