SGR 1806−20
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SGR 1806−20 is a
magnetar A magnetar is a type of neutron star with an extremely powerful magnetic field (~109 to 1011 T, ~1013 to 1015 G). The magnetic-field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays.Ward; Br ...
, a type of
neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
with a very powerful magnetic field, that was discovered in 1979 and identified as a soft gamma repeater. SGR 1806−20 is located about 13
kiloparsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, a ...
s (42,000
light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...
s) from Earth on the far side of the
Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
in the
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...
of Sagittarius. It has a
diameter In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...
of no more than and rotates on its axis every 7.5 seconds ( rotation speed at the equator on the surface). , SGR 1806-20 is the most highly magnetized object ever observed, with a magnetic field of over 1015
gauss Johann Carl Friedrich Gauss (; ; ; 30 April 177723 February 1855) was a German mathematician, astronomer, Geodesy, geodesist, and physicist, who contributed to many fields in mathematics and science. He was director of the Göttingen Observat ...
(G) (1011 tesla) intensity (compared to the Sun's 1–5 G and Earth's 0.25–0.65 G).


Explosion

Forty-two 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). In terms of gamma rays, the burst had an absolute magnitude of around −29. It was the brightest event known to have been sighted on this planet from an origin outside the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...
until GRB 080319B. The magnetar released more energy in one-tenth of a second (1.0 J) than the Sun releases in 150,000 years (4 W × 4.8 s = 1.85 J). Such a burst is thought to be the largest explosion observed in this galaxy by humans since the
SN 1604 SN 1604, also known as Kepler's Supernova, Kepler's Nova or Kepler's Star, was a Type Ia supernova that occurred in the Milky Way, in the constellation Ophiuchus. Appearing in 1604, it is the most recent supernova in the Milky Way galaxy to have ...
, a supernova observed by
Johannes Kepler Johannes Kepler (27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, Natural philosophy, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best know ...
in 1604. The gamma rays struck Earth's
ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...
and created more ionization, which briefly expanded the ionosphere. The quake was equivalent to a magnitude 32 on the
Richter scale The Richter scale (), also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale, is a measure of the strength of earthquakes, developed by Charles Richter in collaboration with Beno Gutenberg, and pr ...
. A similar blast within 3 parsecs (10 light years) of Earth would severely affect the atmosphere, by destroying the
ozone layer The ozone layer or ozone shield is a region of Earth's stratosphere that absorption (electromagnetic radiation), absorbs most of the Sun's ultraviolet radiation. It contains a high concentration of ozone (O3) in relation to other parts of the a ...
and causing mass extinction, and be similar in effect to a 12-
kiloton TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. A ton of TNT equivalent is a unit of energy defined by convention to be (). It is the approximate energy released in the det ...
nuclear blast at . The nearest known magnetar to Earth is 1E 1048.1-5937, located 9,000 light-years away in the constellation Carina.


Location

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 star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectroscopy, spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very ...
s (WC9d and WCL), two blue hypergiants, and LBV 1806-20, one of the brightest/most massive stars in the galaxy.


Planetary system

A 2024 paper posited that periodic gamma-ray and x-ray bursts from the pulsar are caused by a planet orbiting SGR 1806-20. This SGR 1806-20 b would be some kind of rocky world with a mass between 10-18 Earth masses with an orbital period of 398 days and a semi-major axis of 1.18 astronomical units. SGR 1806-20 b is notable for its eccentricity of 0.994, which would make it the most eccentric exoplanet known.


See also

* LBV 1806−20luminous blue variable


Notes


References


External links


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 Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...
'')
Huge 'star-quake' rocks Milky Way
2005-02-18, (
BBC News Online BBC News Online is the website of BBC News, the division of the BBC responsible for newsgathering and production. It is one of the most popular news websites, with 1.2 billion website visits in April 2021, as well as being used by 60% of the U ...
)
Brightest galactic flash ever detected hits Earth
2005-02-18 (
space.com Space.com is an online publication focused on outer space, space exploration, astronomy, skywatching and entertainment, with editorial teams based in the United States and United Kingdom. Launched on July 20, 1999, the website offers live coverag ...
)

2005-02-20 (''
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'') Registration required.
Huge quake cracks star
2005-09-27 (space.com)

(''SpaceDaily'') April 26, 2006 {{DEFAULTSORT:SGR 1806-20 Soft gamma repeaters Sagittarius (constellation) Astronomical objects discovered in 1979 Magnetars Hypothetical planetary systems