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|- style="vertical-align: top;" | Distance | 50,000 light-years (14.5 kiloparsecs) SGR 1806-20 is a magnetar, a particular type of neutron star. It was discovered in 1979 and has been identified as a soft gamma repeater. SGR 1806-20 is located about 14.5 kiloparsecs (50,000 light-years) from Earth on the far side of our Milky Way galaxy in the constellation of Sagittarius. It has a diameter of no more than and rotates on its axis every 7.5 seconds (30,000 km/h rotation speed at the surface). , SGR 1806-20 is the most highly magnetized object ever observed, with a magnetic field over 1015 gauss (1011 tesla) in intensity (compared to the Sun's 1–5 gauss). SGR 1806-20 has a magnetic field that is 1-2 quadrillion (short scale) times stronger than that of the Earth. ==Explosion== A starquake occurred and the radiation from an explosion on the surface of SGR 1806-20 reached Earth on December 27, 2004 (GRB 041227). In terms of gamma rays, the burst had an absolute magnitude around −29. It was the brightest event known to have been sighted on this planet from an origin outside our solar system. The magnetar released more energy in one-tenth of a second (1.3×1039 J) than our sun has released in 100,000 years (4×1026 W × 3.2×1012 s = 1.3×1039 J). Such a burst is thought to be the largest explosion observed by humans in the galaxy since the SN 1604 supernova observed by Johannes Kepler in 1604. The gamma rays struck the Earth ionosphere and created more ionization, which briefly expanded the ionosphere. A similar blast within 3 parsecs (10 light years) of Earth would destroy the ozone layer and would be similar in effect to a 12 kt of TNT (50 TJ) nuclear blast at 7.5 km. The nearest known magnetar to earth is 1E 1048.1-5937, located 9,000 light-years away in the constellation Carina. 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「SGR 1806-20」の詳細全文を読む スポンサード リンク
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