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Cygnus A (3C 405) is a radio galaxy, and one of the strongest radio sources in the sky. It was discovered by Grote Reber in 1939. In 1951, Cygnus A, along with Cassiopeia A, and Puppis A were the first "radio stars" identified with an optical source. Of these, Cygnus A became the first radio galaxy; the other two being nebulae inside the Milky Way.〔Astrophysical Journal, "Identification of the Radio Sources in Cassiopeia (A), Cygnus A, and Puppis A", Baade, W.; Minkowski, R., vol. 119, p.206, ''January 1954'', , 〕 In 1953 Roger Jennison and M K Das Gupta showed it to be a double source. Like all radio galaxies, it contains an active galactic nucleus. Images of the galaxy in the radio portion of the electromagnetic spectrum show two jets protruding in opposite directions from the galaxy's center. These jets extend many times the width of the portion of the host galaxy which emits radiation at visible wavelengths.〔(【引用サイトリンク】 title=The Radio Galaxy Cygnus "A" ) 〕 At the ends of the jets are two lobes with "hot spots" of more intense radiation at their edges. These hot spots are formed when material from the jets collides with the surrounding intergalactic medium. Cygnus A appears in Carl Sagan's ''Contact'' as the result of beings actively creating a galaxy. == References == 〔 * Harris, D. E.; Carilli, C. L.; Perley, R. A. (X-Ray Emission from the Radio Hotspots of Cygnus-A ), Nature Vol. 367, pp. 713, 1994 *(【引用サイトリンク】 work=SIMBAD Astronomical Database ) *(【引用サイトリンク】 title=The powerful radio galaxy Cygnus A ) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cygnus A」の詳細全文を読む スポンサード リンク
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