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 13 kiloparsecs (42,000 light-years)[1] 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 kilometres per hour (19,000 mph) rotation speed at the equator on the surface). As of 2016[update], SGR 1806-20 is the most highly magnetized object ever observed, with a magnetic field of over 1015 gauss (G) (1011 tesla) intensity[2] (compared to the Sun's 1–5 G and Earth's 0.25–0.65 G).
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 08m 39.32s |
| Declination | −20° 24' 39.5"' |
| Apparent magnitude (V) | totally obscured |
| Astrometry | |
| Distance | 42,000 ly (13,000[1] pc) |
| Details | |
| Rotation | 7.55592 s[1] |
| 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 | |
| SIMBAD | data |
Explosion
edit
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).[3] In terms of gamma rays, the burst had an absolute magnitude of around −29.[a] It was the brightest event known to have been sighted on this planet from an origin outside the Solar System until GRB 080319B. 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, a supernova observed by Johannes Kepler in 1604. The gamma rays struck Earth's ionosphere and created more ionization, which briefly expanded the ionosphere. The quake was equivalent to a magnitude 32 on the Richter scale.[4]
A similar blast within 3 parsecs (10 light years) of Earth would severely affect the atmosphere,[3] by destroying the ozone layer and causing mass extinction,[5][6] and be similar in effect to a 12-kiloton nuclear blast at 7.5 kilometres (4.7 mi).[citation needed] The nearest known magnetar to Earth is 1E 1048.1-5937, located 9,000 light-years away in the constellation Carina.
Location
editSGR 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.
Planetary system
editIn 2024, a candidate exoplanet was found orbiting SGR 1806-20. It was found using pulsar timing.
SGR 1806-20 b is 0.0569 Jupiter masses or 18.08 Earth masses. SGR 1806-20 b is probably a hot Neptune with an orbital period of 238 days and a semi-major axis of 0.85 astronomical units. SGR 1806-20 b is notable for its eccentricity of 0.992; it is the most eccentric exoplanet known.[7][8][9]
See also
editNotes
edit- ^ As measured by various space-based and land-based astronomical observatories, including the Swift spacecraft.
References
edit- ^ a b c Manchester, R. N.; Hobbs, G.B.; Teoh, A.; Hobbs, M. "PSR J1808-2024 in the ATNF Pulsar Database". atnf.csiro.edu. Australia Telescope National Facility. Retrieved 9 January 2022.
- ^ "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.
- ^ a b c "Cosmic Explosion Among the Brightest in Recorded History". NASA, Goddard Space Flight Center. 2005-02-18. Retrieved 2011-12-29.
- ^ Plait, Phil (2009-06-18). "OK, so maybe we can be a *little* frightened". Discover Magazine. Retrieved 2024-05-13.
- ^ Bob Berman (4 September 2015). "Weird Object: Magnetar SGR 1806-20". Astronomy.com. Retrieved 30 December 2020.
- ^ "Harvard-Smithsonian Center For Astrophysics: Blast Affected Earth From Halfway Across The Milky Way". ScienceDaily. 23 February 2005. Retrieved 30 December 2020.
- ^ https://exoplanet.eu/catalog/sgr_1806_20_b--10023/
- ^ https://arxiv.org/abs/2403.13333v1
- ^ https://www.aanda.org/articles/aa/full_html/2024/06/aa47828-23.html
External links
edit
- 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)
- [1] 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