The Helix Nebula (also known as NGC 7293 or Caldwell 63) is a planetary nebula (PN) located in the constellationAquarius. Discovered by Karl Ludwig Harding, probably before 1824, this object is one of the closest of all the bright planetary nebulae to Earth[3] The distance, measured by the Gaia mission, is 655±13 light-years.[4] It is similar in appearance to the Cat's Eye Nebula and the Ring Nebula, whose size, age, and physical characteristics are similar to the Dumbbell Nebula, varying only in its relative proximity and the appearance from the equatorial viewing angle.[5] The Helix Nebula has sometimes been referred to as the "Eye of God" in pop culture,[6] as well as the "Eye of Sauron".[7][8]
The Helix Nebula is an example of a planetary nebula, formed by an intermediate to low-mass star, which sheds its outer layers near the end of its evolution. Gases from the star in the surrounding space appear, from our vantage point, as if we are looking down a helix structure. The remnant central stellar core, known as the central star (CS) of the planetary nebula, is destined to become a white dwarf star. The observed glow of the central star is so energetic that it causes the previously expelled gases to brightly fluoresce.
The nebula is in the constellation of Aquarius, and lies about 650 light-years away, spanning about 0.8 parsecs (2.5 light-years). Its age is estimated to be 10600+2300 −1200 years, based on the ratio of its size to its measured expansion rate of 31 km·s−1.[5]
Structure
A 3 dimensional map of carbon monoxide in NGC 7293[9]
Structure and cometary knots are prominent in this Infrared false-color image taken by the Spitzer Space Telescope[10]
The Helix Nebula is thought to be shaped like a prolate spheroid with strong density concentrations toward the filled disk along the equatorial plane, whose major axis is inclined about 21° to 37° from our vantage point. The size of the inner disk is 8×19 arcmin in diameter (0.52 pc); the outer torus is 12×22 arcmin in diameter (0.77 pc); and the outer-most ring is about 25 arcmin in diameter (1.76 pc). The outer-most ring appears flattened on one side due to it colliding with the ambient interstellar medium.[11]
Expansion of the whole planetary nebula structure is estimated to have occurred in the last 6,560 years, and 12,100 years for the inner disk.[12] Spectroscopically, the outer ring's expansion rate is 40 km/s, and about 32 km/s for the inner disk.
Knots
A closer view of knots in the nebula
The location of NGC 7293 (labelled in red)
The Helix Nebula was the first planetary nebula discovered to contain cometary knots.[13] Its main ring contains knots of nebulosity, which have now been detected in several nearby planetary nebulae, especially those with a molecular envelope like the Ring nebula and the Dumbbell Nebula.[14] These knots are radially symmetric (from the CS) and are described as "cometary", each centered on a core of neutral molecular gas and containing bright local photoionization fronts or cusps towards the central star and tails away from it.[15] All tails extend away from the Planetary Nebula Nucleus (PNN) in a radial direction. Excluding the tails, each knot is approximately the size of our Solar system, while each of the cusp knots are optically thick due to Lyc photons from the CS.[2][5][16] There are about 40,000 cometary knots in the Helix Nebula.[17]
The knots are probably the result of Rayleigh-Taylor instability. The low density, high expansion velocity ionized inner nebula is accelerating the denser, slowly expanding, largely neutral material which had been shed earlier when the star was on the Asymptotic Giant Branch.[18]
The excitation temperature varies across the Helix nebula.[19] The rotational-vibrational temperature ranges from 1800 K in a cometary knot located in the inner region of the nebula are about 2.5'(arcmin) from the CS, and is calculated at about 900 K in the outer region at the distance of 5.6'.[19]
Videos
This zoom sequence starts with a wide-field view of the rather empty region of sky around the constellation of Aquarius.
This video compares a new view of the Helix Nebula acquired with the VISTA telescope in infrared light with the more familiar view in visible light from the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory.
^ abcO'Dell, C. R.; McCullough, Peter R.; Meixner, Margaret (2004). "Unraveling the Helix Nebula: Its Structure and Knots". The Astronomical Journal. 128 (5): 2339–2356. arXiv:astro-ph/0407556. Bibcode:2004AJ....128.2339O. doi:10.1086/424621. S2CID 119507454.
^Hora, Joseph L.; Latter, William B.; Smith, Howard A.; Marengo, Massimo (2006). "Infrared Observations of the Helix Planetary Nebula". The Astrophysical Journal. 652 (1): 426–441. arXiv:astro-ph/0607541. Bibcode:2006ApJ...652..426H. doi:10.1086/507944. S2CID 15427995.
^ abcO'Dell, C. R.; Balick, B.; Hajian, A. R.; Henney, W. J.; et al. (2002). "Knots in Nearby Planetary Nebulae". The Astronomical Journal. 123 (6): 3329–3347. Bibcode:2002AJ....123.3329O. doi:10.1086/340726.
^"Urban Legends Reference Pages". The Eye of God. Retrieved 2007-07-16.
^"The Eye of Sauron (aka NGC7293)". Sky and Telescope.
^Nancy Atkinson (4 October 2012). "Eye-Like Helix Nebula Turns Blue in New Image". Universe Today. from the original on 14 July 2014.
^Young, K.;, Cox, P.; Huggins, P. J.; Forveille, T.; Bachiller, R. (1999). "The Molecular Envelope of the Helix Nebula". The Astrophysical Journal. 522 (1): 387–396. Bibcode:1999ApJ...522..387Y. doi:10.1086/307639.{{cite journal}}: CS1 maint: uses authors parameter (link)
^Su, K. Y. L.; Chu, Y.-H.; Rieke, G. H.; Huggins, P. J.; et al. (March 2007). "A Debris Disk around the Central Star of the Helix Nebula?". The Astrophysical Journal. 700 (2): L41–L45. arXiv:astro-ph/0702296. Bibcode:2007ApJ...657L..41S. doi:10.1086/513018. S2CID 15244406.
^Henry, R. B. C.; Kwitter, K. B.; Dufour, R. J. (June 1999). "Morphology and Composition of the Helix Nebula". The Astrophysical Journal. 517 (2): 782–798. arXiv:astro-ph/9901060. Bibcode:1999ApJ...517..782H. doi:10.1086/307215. ISSN 0004-637X.
^O'Dell, C. R.; McCullough, Peter R.; Meixner, Margaret (2004). "Unraveling the Helix Nebula: Its Structure and Knots". The Astronomical Journal. 128 (5): 2339–2356. arXiv:astro-ph/0407556. Bibcode:2004AJ....128.2339O. doi:10.1086/424621. S2CID 119507454.{{cite journal}}: CS1 maint: uses authors parameter (link)
^"APOD: 2008 April 13 - Curious Cometary Knots in the Helix Nebula". apod.nasa.gov. from the original on 2012-05-05.
^O’Dell, C. R.; Balick, B.; Hajian, A. R.; Henney, W. J.; Burkert, A. (June 2002). "Knots in Nearby Planetary Nebulae". The Astronomical Journal. 123 (6): 3329–3347. Bibcode:2002AJ....123.3329O. doi:10.1086/340726.
^Huggins, Patrick; Bachiller, Rafael; Cox, Pierre; Forveille, Thierry (1992). "CO in the globules of the Helix nebula". The Astrophysical Journal Letters. 401: L43–L46. Bibcode:1992ApJ...401L..43H. doi:10.1086/186666.
^O'Dell, C. R.; Balick, B.; Hajian, A. R.; Henney, W. J.; et al. (2003). "Knots in Planetary Nebulae". Winds, Bubbles, and Explosions: A Conference to Honor John Dyson, Pátzcuaro, Michoacán, México, September 9–13, 2002 (Eds. S. J. Arthur & W. J. Henney) Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias. 15: 29–33. Bibcode:2003RMxAC..15...29O.
^Matsuura, M.; Speck, A. K.; McHunu, B. M.; Tanaka, I.; Wright, N. J.; Smith, M. D.; Zijlstra, A. A.; Viti, S.; Wesson, R. (2009-08-01). "A "Firework" of H2Knots in the Planetary Nebula NGC 7293 (The Helix Nebula)". The Astrophysical Journal. 700 (2): 1067–1077. arXiv:0906.2870. Bibcode:2009ApJ...700.1067M. doi:10.1088/0004-637X/700/2/1067. hdl:10355/5140. ISSN 0004-637X. S2CID 119252556.
^Capriotti, Eugene R.; Kendall, Anothony D. (10 May 2006). "The Origin and Physical Properties of the Cometary Knots in NGC 7293". The Astrophysical Journal. 642 (2): 923–932. Bibcode:2006ApJ...642..923C. doi:10.1086/501226. S2CID 120347309. Retrieved 22 November 2020.
^ abMatsuura, M.; Speck, A. K.; Smith, M. D.; Zijlstra, A. A.; et al. (December 2007). "VLT/near-infrared integral field spectrometer observations of molecular hydrogen lines in the knots of the planetary nebula NGC 7293 (the Helix Nebula)". Monthly Notices of the Royal Astronomical Society. 382 (4): 1447–1459. arXiv:0709.3065. Bibcode:2007MNRAS.382.1447M. doi:10.1111/j.1365-2966.2007.12496.x. S2CID 118514953.
External links
Wikimedia Commons has media related to Helix Nebula.
NASA Astronomy Picture of the Day: The Helix Nebula (NGC 7293) (31 December 2009)
NASA Astronomy Picture of the Day: The Helix Nebula (NGC 7293) (10 May 2003)
NASA/JPL-Caltech - The Helix Nebula (NGC 7293)
SEDS - The Helix Nebula (NGC 7293)
NightSkyInfo – The Helix Nebula (NGC 7293)
Snopes - Helix Eye of God - Urban Legend
The Helix Nebula on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
helix, nebula, different, similarly, named, nebula, double, redirects, here, religious, symbol, seeing, other, uses, disambiguation, also, known, 7293, caldwell, planetary, nebula, located, constellation, aquarius, discovered, karl, ludwig, harding, probably, . For the different but similarly named nebula see Double Helix Nebula Eye of God redirects here For the religious symbol see All Seeing Eye of God For other uses see Eye of God disambiguation The Helix Nebula also known as NGC 7293 or Caldwell 63 is a planetary nebula PN located in the constellation Aquarius Discovered by Karl Ludwig Harding probably before 1824 this object is one of the closest of all the bright planetary nebulae to Earth 3 The distance measured by the Gaia mission is 655 13 light years 4 It is similar in appearance to the Cat s Eye Nebula and the Ring Nebula whose size age and physical characteristics are similar to the Dumbbell Nebula varying only in its relative proximity and the appearance from the equatorial viewing angle 5 The Helix Nebula has sometimes been referred to as the Eye of God in pop culture 6 as well as the Eye of Sauron 7 8 Helix Nebula NGC 7293Emission nebulaPlanetary nebulaNGC 7293 seen through several visible filters by Hubble Space TelescopeObservation data J2000 epochRight ascension22h 29m 38 55s 1 Declination 20 50 13 6 1 Distance650 ly 200 1 1 pc Gaia lyApparent magnitude V 7 6 1 Apparent dimensions V 25 2 ConstellationAquariusPhysical characteristicsRadius2 87 ly 0 88 pc 2 lyNotable featuresOne of the nearest PNeDesignationsNGC 7293 1 Caldwell 63See also Lists of nebulae Contents 1 General information 2 Structure 2 1 Knots 3 Videos 4 See also 5 References 6 External linksGeneral information EditThe Helix Nebula is an example of a planetary nebula formed by an intermediate to low mass star which sheds its outer layers near the end of its evolution Gases from the star in the surrounding space appear from our vantage point as if we are looking down a helix structure The remnant central stellar core known as the central star CS of the planetary nebula is destined to become a white dwarf star The observed glow of the central star is so energetic that it causes the previously expelled gases to brightly fluoresce The nebula is in the constellation of Aquarius and lies about 650 light years away spanning about 0 8 parsecs 2 5 light years Its age is estimated to be 10600 2300 1200 years based on the ratio of its size to its measured expansion rate of 31 km s 1 5 Structure Edit A 3 dimensional map of carbon monoxide in NGC 7293 9 Structure and cometary knots are prominent in this Infrared false color image taken by the Spitzer Space Telescope 10 The Helix Nebula is thought to be shaped like a prolate spheroid with strong density concentrations toward the filled disk along the equatorial plane whose major axis is inclined about 21 to 37 from our vantage point The size of the inner disk is 8 19 arcmin in diameter 0 52 pc the outer torus is 12 22 arcmin in diameter 0 77 pc and the outer most ring is about 25 arcmin in diameter 1 76 pc The outer most ring appears flattened on one side due to it colliding with the ambient interstellar medium 11 Expansion of the whole planetary nebula structure is estimated to have occurred in the last 6 560 years and 12 100 years for the inner disk 12 Spectroscopically the outer ring s expansion rate is 40 km s and about 32 km s for the inner disk Knots Edit A closer view of knots in the nebula The location of NGC 7293 labelled in red The Helix Nebula was the first planetary nebula discovered to contain cometary knots 13 Its main ring contains knots of nebulosity which have now been detected in several nearby planetary nebulae especially those with a molecular envelope like the Ring nebula and the Dumbbell Nebula 14 These knots are radially symmetric from the CS and are described as cometary each centered on a core of neutral molecular gas and containing bright local photoionization fronts or cusps towards the central star and tails away from it 15 All tails extend away from the Planetary Nebula Nucleus PNN in a radial direction Excluding the tails each knot is approximately the size of our Solar system while each of the cusp knots are optically thick due to Lyc photons from the CS 2 5 16 There are about 40 000 cometary knots in the Helix Nebula 17 The knots are probably the result of Rayleigh Taylor instability The low density high expansion velocity ionized inner nebula is accelerating the denser slowly expanding largely neutral material which had been shed earlier when the star was on the Asymptotic Giant Branch 18 The excitation temperature varies across the Helix nebula 19 The rotational vibrational temperature ranges from 1800 K in a cometary knot located in the inner region of the nebula are about 2 5 arcmin from the CS and is calculated at about 900 K in the outer region at the distance of 5 6 19 Videos Edit source source source source source source source source source source source source This zoom sequence starts with a wide field view of the rather empty region of sky around the constellation of Aquarius source source source source source source source source source source source source This video compares a new view of the Helix Nebula acquired with the VISTA telescope in infrared light with the more familiar view in visible light from the MPG ESO 2 2 metre telescope at ESO s La Silla Observatory See also EditNew General Catalogue NGC References Edit a b c d NGC 7293 SIMBAD Centre de donnees astronomiques de Strasbourg Retrieved 2006 12 07 a b c O Dell C R McCullough Peter R Meixner Margaret 2004 Unraveling the Helix Nebula Its Structure and Knots The Astronomical Journal 128 5 2339 2356 arXiv astro ph 0407556 Bibcode 2004AJ 128 2339O doi 10 1086 424621 S2CID 119507454 Hora Joseph L Latter William B Smith Howard A Marengo Massimo 2006 Infrared Observations of the Helix Planetary Nebula The Astrophysical Journal 652 1 426 441 arXiv astro ph 0607541 Bibcode 2006ApJ 652 426H doi 10 1086 507944 S2CID 15427995 SIMBAD references a b c O Dell C R Balick B Hajian A R Henney W J et al 2002 Knots in Nearby Planetary Nebulae The Astronomical Journal 123 6 3329 3347 Bibcode 2002AJ 123 3329O doi 10 1086 340726 Urban Legends Reference Pages The Eye of God Retrieved 2007 07 16 The Eye of Sauron aka NGC7293 Sky and Telescope Nancy Atkinson 4 October 2012 Eye Like Helix Nebula Turns Blue in New Image Universe Today Archived from the original on 14 July 2014 Young K Cox P Huggins P J Forveille T Bachiller R 1999 The Molecular Envelope of the Helix Nebula The Astrophysical Journal 522 1 387 396 Bibcode 1999ApJ 522 387Y doi 10 1086 307639 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint uses authors parameter link Su K Y L Chu Y H Rieke G H Huggins P J et al March 2007 A Debris Disk around the Central Star of the Helix Nebula The Astrophysical Journal 700 2 L41 L45 arXiv astro ph 0702296 Bibcode 2007ApJ 657L 41S doi 10 1086 513018 S2CID 15244406 Henry R B C Kwitter K B Dufour R J June 1999 Morphology and Composition of the Helix Nebula The Astrophysical Journal 517 2 782 798 arXiv astro ph 9901060 Bibcode 1999ApJ 517 782H doi 10 1086 307215 ISSN 0004 637X O Dell C R McCullough Peter R Meixner Margaret 2004 Unraveling the Helix Nebula Its Structure and Knots The Astronomical Journal 128 5 2339 2356 arXiv astro ph 0407556 Bibcode 2004AJ 128 2339O doi 10 1086 424621 S2CID 119507454 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint uses authors parameter link APOD 2008 April 13 Curious Cometary Knots in the Helix Nebula apod nasa gov Archived from the original on 2012 05 05 O Dell C R Balick B Hajian A R Henney W J Burkert A June 2002 Knots in Nearby Planetary Nebulae The Astronomical Journal 123 6 3329 3347 Bibcode 2002AJ 123 3329O doi 10 1086 340726 Huggins Patrick Bachiller Rafael Cox Pierre Forveille Thierry 1992 CO in the globules of the Helix nebula The Astrophysical Journal Letters 401 L43 L46 Bibcode 1992ApJ 401L 43H doi 10 1086 186666 O Dell C R Balick B Hajian A R Henney W J et al 2003 Knots in Planetary Nebulae Winds Bubbles and Explosions A Conference to Honor John Dyson Patzcuaro Michoacan Mexico September 9 13 2002 Eds S J Arthur amp W J Henney Revista Mexicana de Astronomia y Astrofisica Serie de Conferencias 15 29 33 Bibcode 2003RMxAC 15 29O Matsuura M Speck A K McHunu B M Tanaka I Wright N J Smith M D Zijlstra A A Viti S Wesson R 2009 08 01 A Firework of H2Knots in the Planetary Nebula NGC 7293 The Helix Nebula The Astrophysical Journal 700 2 1067 1077 arXiv 0906 2870 Bibcode 2009ApJ 700 1067M doi 10 1088 0004 637X 700 2 1067 hdl 10355 5140 ISSN 0004 637X S2CID 119252556 Capriotti Eugene R Kendall Anothony D 10 May 2006 The Origin and Physical Properties of the Cometary Knots in NGC 7293 The Astrophysical Journal 642 2 923 932 Bibcode 2006ApJ 642 923C doi 10 1086 501226 S2CID 120347309 Retrieved 22 November 2020 a b Matsuura M Speck A K Smith M D Zijlstra A A et al December 2007 VLT near infrared integral field spectrometer observations of molecular hydrogen lines in the knots of the planetary nebula NGC 7293 the Helix Nebula Monthly Notices of the Royal Astronomical Society 382 4 1447 1459 arXiv 0709 3065 Bibcode 2007MNRAS 382 1447M doi 10 1111 j 1365 2966 2007 12496 x S2CID 118514953 External links Edit Wikimedia Commons has media related to Helix Nebula NASA Astronomy Picture of the Day The Helix Nebula NGC 7293 31 December 2009 NASA Astronomy Picture of the Day The Helix Nebula NGC 7293 10 May 2003 NASA JPL Caltech The Helix Nebula NGC 7293 SEDS The Helix Nebula NGC 7293 NightSkyInfo The Helix Nebula NGC 7293 Snopes Helix Eye of God Urban Legend The Helix Nebula on WikiSky DSS2 SDSS GALEX IRAS Hydrogen a X Ray Astrophoto Sky Map Articles and images Helix Nebula NGC 7293 at Constellation Guide Portals Astronomy Stars Outer space Retrieved from https en wikipedia org w index php title Helix Nebula amp oldid 1124309257, wikipedia, wiki, book, books, library,
