SGR 1806-20

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In astronomy, SGR 1806-20 is a magnetar, a particular type of neutron star. It 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 20 kilometres (12 miles) and rotates on its axis every 7.5 seconds.

This is where SGR 1806-20 would appear in the sky if it were visible to human eyes.

On December 27, 2004, the radiation from an explosion on the surface of SGR 1806-20 reached Earth. In terms of gamma rays the burst was brighter than a full moon and had an absolute magnitude of around −29¹. It was the brightest event known to have impacted this planet from an origin outside our solar system. The gamma rays struck the ionosphere and created more ionization which briefly expanded the ionosphere. 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.

A similar blast within 3 parsecs (10 light years) of earth would destroy the ozone layer and would be similar to a 12 kt of TNT (50 TJ) nuclear blast at 7.5 km. Fortunately, the nearest known magnetar to earth is 1E 2259+586, 4 kiloparsecs (13,000 light years) away.

External links

[Huge 'star-quake' rocks Milky Way], 2005-02-18, (BBC News Online)
[Brightest galactic flash ever detected hits Earth] 2005-02-18 (space.com)
[link] 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) Apr 26, 2006

Notes

Note 1: As measured by various space-based and land-based astronomical observatories, including the Swift spacecraft.

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