Krabbetågen
Krabbetågen (M1; objekt nr. 1 i Messiers katalog, også kendt som NGC 1952 og Taurus A), er resterne af en supernova som kan ses i stjernebilledet Tyren, 6.300 lysår fra Jorden. Selve eksplosionen blev observeret i 1054 af bl.a. kinesiske og arabiske astronomer, og i 1731 fandt den engelske læge og astronom John Bevis Krabbetågen netop det sted på himlen hvor man i 1054 så supernovaeksplosionen. I nyere tid har man fundet den egentlige rest af supernovaen midt i den synlige tåge; en neutronstjerne der snurrer om sig selv 30,2 gange i sekundet, og for hver omdrejning sender en puls af alt fra radiobølger til røntgenstråling i vores retning (en såkaldt pulsar). Pulsaren blev opdaget, som den anden kendte pulsar i januar 1969. Den var dog tidligere blevet observeret af Minkowski i 1942. Han var dog ikke klar over betydningen af sin opdagelse.
Under gode forhold kan M1 lokaliseres med en god håndkikkert, men den ses bedre med et teleskop. Tågen måler 11 lysår på den lange led, hvilket set fra Jorden andrager 6 bueminutter; en femtedel af fuldmånens tilsyneladende diameter.
Supernovaeksplosionen var den endelige undergang for en stjerne med formodentlig mellem 8 og 12 gange så stor masse som vor egen Sol: De filamenter og "trevler" man kan se i Krabbetågen i dag, er hvad der er tilbage af de ydre dele af denne stjerne; de består af ioniseret helium og brint, samt kulstof, ilt, kvælstof, jern, neon og svovl. Dette stof bevæger sig væk fra eksplosionsstedet med en fart af omkring 1.500 kilometer i sekundet.
Det diffuse, blågrønne lys skyldes synkrotronstråling fra elektroner der bevæger sig med henved halvdelen af lysets hastighed, alt imens deres bane afbøjes af magnetfelter.
Eksterne henvisninger
Koordinater: 
5h 34m 31.97s, +22° 00′ 52.1″
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This is a mosaic image, one of the largest ever taken by NASA's Hubble Space Telescope, of the Crab Nebula, a six-light-year-wide expanding remnant of a star's supernova explosion. Japanese and Chinese astronomers recorded this violent event in 1054 CE.
The orange filaments are the tattered remains of the star and consist mostly of hydrogen. The rapidly spinning neutron star embedded in the center of the nebula is the dynamo powering the nebula's eerie interior bluish glow. The blue light comes from electrons whirling at nearly the speed of light around magnetic field lines from the neutron star. The neutron star, like a lighthouse, ejects twin beams of radiation that appear to pulse 30 times a second due to the neutron star's rotation. A neutron star is the crushed ultra-dense core of the exploded star.
The Crab Nebula derived its name from its appearance in a drawing made by Irish astronomer Lord Rosse in 1844, using a 36-inch telescope. When viewed by Hubble, as well as by large ground-based telescopes such as the European Southern Observatory's Very Large Telescope, the Crab Nebula takes on a more detailed appearance that yields clues into the spectacular demise of a star, 6,500 light-years away.
The newly composed image was assembled from 24 individual Wide Field and Planetary Camera 2 exposures taken in October 1999, January 2000, and December 2000. The colors in the image indicate the different elements that were expelled during the explosion. Blue in the filaments in the outer part of the nebula represents neutral oxygen, green is singly-ionized sulfur, and red indicates doubly-ionized oxygen.
Forfatter/Opretter: Fork of free file File:Celestia.png, Licens: GPL
Image of the planet Jupiter and one of its moons
(c) ESA/Hubble, CC BY 4.0
This captivating new image shows the Crab Nebula in bright neon colours. The unusual image was produced by combining data from telescopes spanning nearly the entire electromagnetic spectrum, from radio waves to X-rays. The Karl G. Jansky Very Large Array (VLA) provided information about the nebula gathered in the radio regime (coloured in red). NASA’s Spitzer Space Telescope took images in the infrared (yellow). The NASA/ESA Hubble Space Telescope provided the images made in optical wavelengths (coloured in green). ESA’s XMM-Newton telescope observed the Crab Nebula in the ultraviolet (blue) and NASA’s Chandra X-ray Observatory provided the data for X-ray radiation (purple).
The Crab Nebula, located 6500 light-years from Earth in the constellation of Taurus (The Bull), is the result of a supernova explosion which was observed by Chinese and other astronomers in 1054. At its centre is a pulsar: a super-dense neutron star, spinning once every 33 milliseconds, shooting out rotating lighthouse-like beams of radio waves and visible light.
Surrounding the pulsar lies a mix of material; some of it was originally expelled from the star before it went supernova, and the rest was ejected during the explosion itself. Fast-moving winds of particles fly off from the neutron star, energising the dust and gas around it. These different layers and intricacies of the nebula can be observed in all of the different wavelengths of light.