SGR 1806−20

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SGR 1806−20
SGR 1806-20 108685main SRB1806 20rev2.jpg
This is where SGR 1806-20 would appear in the sky if it were visible to human eyes.
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension 18h 08m 39.32s
Declination −20° 24' 39.5"'
Apparent magnitude (V) totally obscured
Distance50,000 ly
(14,500[citation needed] pc)
Other designations
GRB 790107, INTEGRAL1 84, AX 1805.7-2025 GRB 970912, INTREF 882, CXOU J180839.3-202439, HETE Trigger 1566, KONUS 07.01.79, EQ 1805.7-2025, HETE Trigger 3801, PSR J1808−2024, GBS 1806-20, HETE Trigger 3800, RX J1808.6−2024
Database references

SGR 1806−20 is a magnetar, a type of neutron star with a very powerful magnetic field, that was discovered in 1979 and 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 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, SGR 1806-20 is the most highly magnetized object ever observed, with a magnetic field over 1015 gauss (G) (1011 tesla) in intensity[1] (compared to the Sun's 1–5 G and Earth's 0.25–0.65 G).


Artists impression of the surrounding cloud bubble
Artist rendering of central neutron star

Fifty thousand years after a starquake occurred on the surface of SGR 1806-20, the radiation from the resultant explosion reached Earth on December 27, 2004 (GRB 041227).[2] 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 (1.0×1040 J) than the Sun releases in 150,000 years (4×1026 W × 4.8×1012 s = 1.85×1039 J).[3] Such a burst is thought to be the largest explosion observed in this galaxy by humans since the SN 1604 supernova observed by Johannes Kepler in 1604. The gamma rays struck Earth's 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 be similar in effect to a 12-kiloton nuclear blast at 7.5 kilometers. 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.

See also[edit]


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


  1. ^ "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.
  2. ^ "Cosmic Explosion Among the Brightest in Recorded History". NASA, Goddard Space Flight Center. 2005-02-18. Retrieved 2011-12-29.
  3. ^ NASA - Cosmic Explosion Among the Brightest in Recorded History

External links[edit]

Coordinates: Sky map 18h 08m 39.32s, −20° 24′ 39.5″