Sagittarius A

Sagittarius A
Strongest source of cosmic radio waves, lying in the direction of the constellation Sagittarius.

Discovered by Karl Jansky in 1932, it has been identified as the nucleus of the Milky Way Galaxy. The region is relatively small and constitutes an intense source of infrared radiation thought to be emitted partly by stars and partly by dust around them. Within the region is a much smaller radio source, Sagittarius (Sgr) A*, which appears to mark the centre of the Galaxy. Observations indicate that the galactic nucleus contains a black hole with a mass of one million to several million times that of the Sun; they also provide a strong case that Sgr A* is the black hole. The activity at the Galaxy's centre resembles that of an active galactic nucleus but on a much smaller scale.

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 strongest source of cosmic radio waves in the Milky Way Galaxy, originating from the direction of the constellation Sagittarius. One component of the source, known as Sagittarius A West, has been identified as coming from the direction of the nucleus of the Milky Way Galaxy. Most of the radio radiation is from a synchrotron mechanism, indicating the presence of free electrons and magnetic fields. A compact, extremely bright central point source is designated Sagittarius A*. X-ray, infrared (infrared radiation), spectroscopic, and radio interferometric investigations have indicated the very small dimensions of this region. Infrared observations of stars orbiting around the position of Sagittarius A* demonstrate the presence of a black hole with a mass equivalent to 4,310,000 Suns (Sun). These properties are similar to those of other galaxies with active nuclei (e.g., Seyfert galaxies (Seyfert galaxy)) but on a smaller scale.

Paul W. Hodge
 

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Universalium. 2010.

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  • Sagittarius A* — Photographie de Sagittarius A* (au centre) et de deux échos lumineux provenant d une explosion récente (entourés) Données d’observation (Époque J2000.0) Constellation …   Wikipédia en Français

  • Sagittarius — may refer to: *Sagittarius (astrology), an astrological sign *Sagittarius (constellation), a constellation *Sagittarius A, a complex radio source at the centre of the Milky Way *Sagittarius Dwarf Elliptical Galaxy *Sagittarius (band), a 60 s… …   Wikipedia

  • Sagittarius A — (ou Sgr A) est une source d émission radio complexe située au centre de notre Galaxie. Elle tire son nom de sa situation dans la constellation du Sagittaire. Elle est formée de trois composants : Sagittarius A Est, les restes d une supernova …   Wikipédia en Français

  • Sagittarius B2 — (Sgr B2) is a giant molecular cloud of gas and dust that is located about 120 parsecs from the center of the Milky Way. This complex is the largest molecular cloud in the vicinity of the core and one of the largest in the galaxy, spanning a… …   Wikipedia

  • Sagittarius — Sag it*ta ri*us, n. [L., literally, an archer, fr. sagittarius belonging to an arrow, fr. sagitta an arrow.] (Astron.) (a) The ninth of the twelve signs of the zodiac, which the sun enters about November 22, marked thus [[sagittarius]] in… …   The Collaborative International Dictionary of English

  • Sagittarius x-4 — Pour les articles homonymes, voir X 4. Sagittarius X 4, ou Sgr X 4 est une binaire X à faible masse situé au sein de l amas globulaire NGC 6624, dans la constellation du Sagittaire. Avec une période orbitale de seulement… …   Wikipédia en Français

  • Sagittarius — (Марина ди Рагуза,Италия) Категория отеля: Адрес: Via Pescara 30, 97010 Марина ди Рагуз …   Каталог отелей

  • Sagittarius A — Sagittarius A,   Abkürzung Sgr A, Radioquellengebiet im Zentralbereich des Milchstraßensystems mit der Quelle Sagittarius A* als eigentliches Zentrum (galaktisches Zentrum). Die Beobachtung des galaktischen Zentrums ist nur mit den Mitteln der… …   Universal-Lexikon

  • Sagittarius — constellation, late 14c., from L., lit. archer, properly pertaining to arrows, from sagitta arrow, which probably is from a pre Latin Mediterranean language. Meaning person born under Sagittarius (properly Sagittarian) is attested from 1940 …   Etymology dictionary

  • Sagittarius — [saj΄ə ter′ē əs] n. [ME < L sagittarius, archer < sagitta, arrow] 1. a large S constellation in the brightest part of the Milky Way, beyond which lies the center of our galaxy; the Archer 2. the ninth sign of the zodiac, entered by the sun… …   English World dictionary

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