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Epoch J2000 Equinox J2000
|Right ascension||18h 08m 39.32s|
|Declination||−20° 24' 39.5"'|
|Apparent magnitude (V)||totally obscured|
|Distance||50,000 light-years (14.5 kiloparsecs)|
|Luminosity||3000000 L☉|
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 the Milky Way galaxy in the constellation of Sagittarius. It has a diameter of no more than 20 kilometres (12 mi) and rotates on its axis every 7.5 seconds (30,000 km/h rotation speed at the surface). As of 2016[update], 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.
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 −291. It was the brightest event known to have been sighted on this planet from an origin outside the Solar System. The magnetar released more energy in one-tenth of a second (1.3×1039 J) than the 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 in the galaxy by humans 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.
SGR 1806-20 lies at the core of radio nebula G10.0-0.3 and is a member of an open cluster named after it, itself a component of W31, one of the largest H II regions in the Milky Way. Cluster 1806-20 is made up of some highly unusual stars, including at least two carbon-rich Wolf–Rayet stars (WC9d and WCL), two blue hypergiants, and LBV 1806-20, one of the brightest/most massive stars in the galaxy.
- "Top story – Scientists measure the most powerful magnet known". NASA, Goddard Space Flight Center. 2002-11-04. Archived from the original on 2010-04-28. Retrieved 2011-12-29.
- "Cosmic Explosion Among the Brightest in Recorded History". NASA, Goddard Space Flight Center. 2005-02-18. Retrieved 2011-12-29.
|Wikimedia Commons has media related to SGR 1806-20.|
- Anniversary of a Cosmic Blast (Phil Plait Dec. 27, 2012)
- An exceptionally bright flare from SGR 1806-20 and the origins of short-duration big gamma-ray bursts, 2005-04-28 (Nature)
- Huge 'star-quake' rocks Milky Way, 2005-02-18, (BBC News Online)
- Brightest galactic flash ever detected hits Earth 2005-02-18 (space.com)
-  2005-02-20 (The Age) Registration required.
- Huge quake cracks star 2005-09-27 (space.com)
- NASA Sees Hidden Structure Of Neutron Star In Starquake (SpaceDaily) April 26, 2006