Magnetar
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En magnetar (en slags "SGR", Soft gamma repeater eller "AXP", Anomalous X-ray Pulsar) er en speciel type af neutronstjerne som har et stærkt magnetfelt. Jordens magnetfelt varier mellem 30-60 mikrotesla, mens en magnetars magnetfelt er helt oppe på 100 milliarder tesla. Magnetfeltet om en magnetar er så kraftigt at det faktisk får stjernen til at rotere langsommere. Normale neutronstjerner roterer en gang om sig selv ca. hvert millisekund, en magnetar roterer en del langsommere pga. deres magnetfelt, de roterer en gang om sig selv hvert 10. sekund. I 2020 var den hurtigste roterende magnetar 1,4 sekunder om en hel omgang.[1]
Teorien omkring disse objekter blev formuleret af Robert Duncan og Christopher Thompson i 1987. Da de skulle præsentere deres idé på en videnskabelig konference i 1992, fik de kun tre minutters taletid. De blev siden gjort til grin af andre astrofysikere og blev henvist til fjerne hjørner af andre konferencer, indtil deres teori blev accepteret, efter at de første observationer blev gjort. Der er blevet observeret 12 magnetarkandidater i mælkevejen, vores egen galakse, samt den Store Magellanske Sky og den Lille Magellanske Sky, der begge ligger meget tæt på mælkevejen.
Det formodes, at hver tiende supernovaeksplosion resulterer i en magnetar i stedet for de mere almindelige neutronstjerner eller pulsarer.
Referencer
- ^ July 7, 2020, scitechdaily.com: Mysterious Spinning Neutron Star Detected in the Milky Way With Extraordinary Properties Citat: "...Spinning once every 1.4 seconds, it’s the fastest spinning magnetar known, and possibly one of the youngest neutron stars in the Milky Way. It also emits radio pulses like those seen from pulsars — another type of rotating neutron star in our galaxy. At the time of this detection, only four other radio-pulse-emitting magnetars were known, making Swift J1818.0–1607 an extremely rare discovery..."
- Powerful ancient explosions explain new class of supernovae. PHYS ORG
- NASA: "Magnetar" discovery solves 19-year-old mystery Arkiveret 11. marts 2009 hos Wayback Machine Citat: "...suggested a magnetic field strength of about 800 trillion Gauss...").
- Robert C. Duncan, University of Texas at Austin: 'Magnetars', Soft Gamma Repeaters & Very Strong Magnetic Fields Arkiveret 11. juni 2007 hos Wayback Machine
- NASA Astrophysics Data System (ADS): Duncan & Thompson, Ap.J. 392, L9) 1992
- NASA ADS, 1999: Discovery of a Magnetar Associated with the Soft Gamma Repeater SGR 1900+14
- Physics Web: January 2003: Strongest magnet in the cosmos Arkiveret 29. december 2003 hos Wayback Machine Citat: "...This discovery represents a new frontier in neutron-star astrophysics. Since magnetars slow down rapidly, only a handful of them will be active and observable at any one time..."
- 2004-01-09, ScienceDaily: Magnetars, The Most Magnetic Stars Known, More Common Than Previously Thought Citat: "...Magnetars represent a new way for a star to shine, which makes this a fascinating field..."
Eksterne henvisninger
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