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{{short description|Planetary nebula in the constellation Aquarius}} |
{{short description|Planetary nebula in the constellation Aquarius}} |
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{{For|the different but similarly named nebula|Double Helix Nebula}} |
{{For|the different but similarly named nebula|Double Helix Nebula}} |
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{{Redirect|Eye of God}} |
{{Redirect|Eye of God|the religious symbol|All-Seeing Eye of God|other uses}} |
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{{Planetary nebula |
{{Planetary nebula |
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| name = Helix Nebula, NGC 7293 |
| name = Helix Nebula, NGC 7293 |
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| type = Planetary |
| type = Planetary |
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| image = |
| image = File:NGC7293 (2004).jpg |
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| ⚫ | | caption= NGC 7293 seen through several visible filters by [[Hubble Space Telescope]] |
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| ⚫ |
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| credit = |
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| credit = [[NASA]], [[JPL]], [[Caltech]], Kate Su (Steward Obs., U. Arizona). |
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| epoch = [[J2000]] |
| epoch = [[J2000]] |
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| ra = {{RA|22|29|38.55}}<ref name="simbad">{{cite simbad |
| ra = {{RA|22|29|38.55}}<ref name="simbad">{{cite simbad |
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| access-date=2006-12-07}}</ref> |
| access-date=2006-12-07}}</ref> |
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| dec = {{DEC|-20|50|13.6}}<ref name="simbad" /> |
| dec = {{DEC|-20|50|13.6}}<ref name="simbad" /> |
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| dist_ly = {{val| |
| dist_ly = {{val|200|1|ul=pc}} ({{val|650|3}}) |
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| appmag_v = +7.6<ref name="simbad" /> |
| appmag_v = +7.6<ref name="simbad" /> |
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| size_v = 25′<ref name="ODelletal2004" /> |
| size_v = 25′<ref name="ODelletal2004" /> |
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| names = [[New General Catalogue|NGC]] 7293<ref name="simbad" /> [[Caldwell catalogue|Caldwell]] 63 |
| names = [[New General Catalogue|NGC]] 7293<ref name="simbad" /> [[Caldwell catalogue|Caldwell]] 63 |
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}} |
}} |
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The '''Helix Nebula''' (also known as '''NGC 7293''' or '''Caldwell 63''') is a [[planetary nebula]] (PN) located in the [[constellation]] [[Aquarius (constellation)|Aquarius]]. Discovered by [[Karl Ludwig Harding]], |
The '''Helix Nebula''' (also known as '''NGC 7293''' or '''Caldwell 63''') is a [[planetary nebula]] (PN) located in the [[constellation]] [[Aquarius (constellation)|Aquarius]]. Discovered by [[Karl Ludwig Harding]], most likely before 1824, this object is one of the closest of all the bright [[planetary nebula]]e to Earth.<ref name="Horaetal2006">{{cite journal |
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| author=Hora, Joseph L. |
| author=Hora, Joseph L. |
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| author2=Latter, William B. |
| author2=Latter, William B. |
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| title=Urban Legends Reference Pages |
| title=Urban Legends Reference Pages |
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| work=The Eye of God |
| work=The Eye of God |
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| date=5 February 2004 |
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| url=http://www.snopes.com/photos/space/eyeofgod.asp |
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| access-date=2007-07-16 |
| access-date=2007-07-16 |
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}}</ref> as well as the "[[Eye of Sauron]]".<ref>{{cite journal |
}}</ref> as well as the "[[Eye of Sauron]]".<ref>{{cite journal |
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==General information== |
==General information== |
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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 |
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 Earth's perspective, 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]]. |
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The nebula is in the constellation of [[Aquarius (constellation)|Aquarius]], and lies about 650 [[light-year]]s away, spanning about 0.8 [[parsec]]s (2.5 light-years). Its age is estimated to be {{val|10600|+2300|-1200}} years, based on the ratio of its size to its measured expansion rate of 31 km·s<sup>−1</sup>.<ref name="ODelletal2002" /> |
The nebula is in the constellation of [[Aquarius (constellation)|Aquarius]], and lies about 650 [[light-year]]s away, spanning about 0.8 [[parsec]]s (2.5 light-years). Its age is estimated to be {{val|10600|+2300|-1200}} years, based on the ratio of its size to its measured expansion rate of 31 km·s<sup>−1</sup>.<ref name="ODelletal2002" /> |
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==Structure== |
==Structure== |
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[[File:Helix3D.png|thumb|right|A 3 dimensional map of carbon monoxide in NGC 7293<ref>{{cite journal | bibcode = 1999ApJ...522..387Y | title=The Molecular Envelope of the Helix Nebula | journal=The Astrophysical Journal | volume=522 | pages=387–396 | year=1999 | |
[[File:Helix3D.png|thumb|right|A 3 dimensional map of carbon monoxide in NGC 7293<ref>{{cite journal | bibcode = 1999ApJ...522..387Y | title=The Molecular Envelope of the Helix Nebula | journal=The Astrophysical Journal | volume=522 | pages=387–396 | year=1999 |author1=Young, K. |author2=Cox, P. |author3=Huggins, P. J. |author4=Forveille, T. |author5=Bachiller, R. | issue=1 | doi=10.1086/307639| doi-access=free }}</ref>]] |
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| ⚫ |
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| ⚫ | [[File:Comets Kick up Dust in Helix Nebula (PIA09178).jpg|thumb|left|Structure and cometary knots are prominent in this Infrared false-color image taken by the [[Spitzer Space Telescope]]<ref name="Suetal2007">{{cite journal | bibcode = 2007ApJ...657L..41S | title = A Debris Disk around the Central Star of the Helix Nebula? | date = March 2007 | journal = The Astrophysical Journal | volume = 700 | issue = 2 | pages = L41–L45 | doi = 10.1086/513018 | author = Su, K. Y. L. | display-authors = 4 | author2 = Chu, Y.-H. | author3 = Rieke, G. H. | author4 = Huggins, P. J. | author5 = Gruendl, R. | author6 = Napiwotzki, R. | author7 = Rauch, T. | author8 = Latter, W. B. | author9 = Volk, K. |arxiv = astro-ph/0702296 | s2cid = 15244406 }}</ref>]] |
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| ⚫ | [[File:NGC7293Location.png|thumb|left|The location of NGC 7293 (labelled in red)]] |
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The Helix Nebula is thought to be shaped like a [[prolate spheroid]] with strong density concentrations toward the filled disk along the [[equator]]ial 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]].<ref>{{Cite journal|last1=Henry|first1=R. B. C.|last2=Kwitter|first2=K. B.|last3=Dufour|first3=R. J.|date=June 1999|title=Morphology and Composition of the Helix Nebula|url=http://stacks.iop.org/0004-637X/517/i=2/a=782|journal=The Astrophysical Journal|volume=517|issue=2|pages=782–798|doi=10.1086/307215|arxiv=astro-ph/9901060|bibcode=1999ApJ...517..782H|issn=0004-637X|doi-access=free}}</ref> |
The Helix Nebula is thought to be shaped like a [[prolate spheroid]] with strong density concentrations toward the filled disk along the [[equator]]ial 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]].<ref>{{Cite journal|last1=Henry|first1=R. B. C.|last2=Kwitter|first2=K. B.|last3=Dufour|first3=R. J.|date=June 1999|title=Morphology and Composition of the Helix Nebula|url=http://stacks.iop.org/0004-637X/517/i=2/a=782|journal=The Astrophysical Journal|volume=517|issue=2|pages=782–798|doi=10.1086/307215|arxiv=astro-ph/9901060|bibcode=1999ApJ...517..782H|issn=0004-637X|doi-access=free}}</ref> |
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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.<ref |
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.<ref name="ODelletal2004" /> Spectroscopically, the outer ring's expansion rate is 40 km/s, and about 32 km/s for the inner disk. |
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===Knots=== |
===Knots=== |
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[[File:Close-Up of the Helix Nebula.jpg|thumb|A closer view of knots in the nebula]] |
[[File:Close-Up of the Helix Nebula.jpg|thumb|A closer view of knots in the nebula]] |
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| ⚫ |
[[File:NGC7293Location.png|thumb| |
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The Helix Nebula was the first planetary nebula discovered to contain [[cometary knot]]s.<ref>{{cite web|url=http://apod.nasa.gov/apod/ap080413.html|title=APOD: 2008 April 13 - Curious Cometary Knots in the Helix Nebula|website=apod.nasa.gov|url-status=live|archive-url=https://web.archive.org/web/20120505083443/http://apod.nasa.gov/apod/ap080413.html |archive-date=2012-05-05}}</ref> 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|Ring nebula]] and the [[Dumbbell Nebula]].<ref>{{Cite journal|last1=O’Dell|first1=C. R.|last2=Balick|first2=B.|last3=Hajian|first3=A. R.|last4=Henney|first4=W. J.|last5=Burkert|first5=A.|date=June 2002|title=Knots in Nearby Planetary Nebulae|url=http://stacks.iop.org/1538-3881/123/i=6/a=3329|journal=The Astronomical Journal|volume=123|issue=6|pages=3329–3347|doi=10.1086/340726|bibcode=2002AJ....123.3329O|doi-access=free}}</ref> |
The Helix Nebula was the first planetary nebula discovered to contain [[cometary knot]]s.<ref>{{cite web|url=http://apod.nasa.gov/apod/ap080413.html|title=APOD: 2008 April 13 - Curious Cometary Knots in the Helix Nebula|website=apod.nasa.gov|url-status=live|archive-url=https://web.archive.org/web/20120505083443/http://apod.nasa.gov/apod/ap080413.html |archive-date=2012-05-05}}</ref> 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|Ring nebula]] and the [[Dumbbell Nebula]].<ref>{{Cite journal|last1=O’Dell|first1=C. R.|last2=Balick|first2=B.|last3=Hajian|first3=A. R.|last4=Henney|first4=W. J.|last5=Burkert|first5=A.|date=June 2002|title=Knots in Nearby Planetary Nebulae|url=http://stacks.iop.org/1538-3881/123/i=6/a=3329|journal=The Astronomical Journal|volume=123|issue=6|pages=3329–3347|doi=10.1086/340726|bibcode=2002AJ....123.3329O|doi-access=free}}</ref> |
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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.<ref name="Huggins1992">{{cite journal |
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| author=Huggins, Patrick |
| author=Huggins, Patrick |
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| author2=Bachiller, Rafael |
| author2=Bachiller, Rafael |
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| Line 99: | Line 108: | ||
| bibcode=1992ApJ...401L..43H |
| bibcode=1992ApJ...401L..43H |
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| doi=10.1086/186666 |
| doi=10.1086/186666 |
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}}</ref> All tails extend away from the Planetary Nebula Nucleus (PNN) in a radial direction. Excluding the tails, each knot is approximately the size of |
}}</ref> All tails extend away from the Planetary Nebula Nucleus (PNN) in a radial direction. Excluding the tails, each knot is approximately the size of the [[Solar System]], while each of the cusp knots are optically thick due to [[Lyc photon]]s from the CS.<ref name="ODelletal2004">{{cite journal |
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| author=O'Dell, C. R. |
| author=O'Dell, C. R. |
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| author2=McCullough, Peter R. |
| author2=McCullough, Peter R. |
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| Line 112: | Line 121: | ||
| doi=10.1086/424621 |
| doi=10.1086/424621 |
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|arxiv = astro-ph/0407556 | s2cid=119507454 |
|arxiv = astro-ph/0407556 | s2cid=119507454 |
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}}</ref><ref name="ODelletal2002" /><ref name="ODelletal2003">{{cite |
}}</ref><ref name="ODelletal2002" /><ref name="ODelletal2003">{{cite book |
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| author=O'Dell, C. R. |
| author=O'Dell, C. R. |
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| display-authors=4 |
| display-authors=4 |
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| Line 119: | Line 128: | ||
| author4=Henney, W. J. |
| author4=Henney, W. J. |
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| author5=Burkert, A. |
| author5=Burkert, A. |
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| |
| chapter=Knots in Planetary Nebulae |
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| |
| title=Winds, Bubbles, and Explosions: A Conference to Honor John Dyson, Pátzcuaro, Michoacán, México, September 9–13, 2002 |
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| editor-last1=Arthur |
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| editor-first1=Jane |
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| editor-last2=Henney |
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| editor-first2=William |
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| series=Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias |
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| publisher= Instituto de Astronomía, Universidad Nacional Autónoma de México |
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| date=2003 |
| date=2003 |
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| volume=15 |
| volume=15 |
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| Line 127: | Line 142: | ||
}}</ref> There are about 40,000 cometary knots in the Helix Nebula.<ref>{{Cite journal|last1=Matsuura|first1=M.|last2=Speck|first2=A. K.|last3=McHunu|first3=B. M.|last4=Tanaka|first4=I.|last5=Wright|first5=N. J.|last6=Smith|first6=M. D.|last7=Zijlstra|first7=A. A.|last8=Viti|first8=S.|last9=Wesson|first9=R.|title=A "Firework" of H2Knots in the Planetary Nebula NGC 7293 (The Helix Nebula)|date=2009-08-01|url=http://stacks.iop.org/0004-637X/700/i=2/a=1067?key=crossref.e2bfcad2bbe1c7202b459debb74936a6|journal=The Astrophysical Journal|volume=700|issue=2|pages=1067–1077|doi=10.1088/0004-637X/700/2/1067|arxiv=0906.2870|bibcode=2009ApJ...700.1067M|issn=0004-637X|hdl=10355/5140|s2cid=119252556 |hdl-access=free}}</ref> |
}}</ref> There are about 40,000 cometary knots in the Helix Nebula.<ref>{{Cite journal|last1=Matsuura|first1=M.|last2=Speck|first2=A. K.|last3=McHunu|first3=B. M.|last4=Tanaka|first4=I.|last5=Wright|first5=N. J.|last6=Smith|first6=M. D.|last7=Zijlstra|first7=A. A.|last8=Viti|first8=S.|last9=Wesson|first9=R.|title=A "Firework" of H2Knots in the Planetary Nebula NGC 7293 (The Helix Nebula)|date=2009-08-01|url=http://stacks.iop.org/0004-637X/700/i=2/a=1067?key=crossref.e2bfcad2bbe1c7202b459debb74936a6|journal=The Astrophysical Journal|volume=700|issue=2|pages=1067–1077|doi=10.1088/0004-637X/700/2/1067|arxiv=0906.2870|bibcode=2009ApJ...700.1067M|issn=0004-637X|hdl=10355/5140|s2cid=119252556 |hdl-access=free}}</ref> |
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The knots are probably the result of [[Rayleigh-Taylor instability]]. |
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]].<ref>{{cite journal |last1=Capriotti |first1=Eugene R. |last2=Kendall |first2=Anothony D. |title=The Origin and Physical Properties of the Cometary Knots in NGC 7293 |journal=The Astrophysical Journal |date=10 May 2006 |volume=642 |number = 2|pages=923–932 |doi=10.1086/501226 |bibcode=2006ApJ...642..923C |s2cid=120347309 |url=https://iopscience.iop.org/article/10.1086/501226/pdf |access-date=22 November 2020|doi-access=free }}</ref> |
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The [[excitation temperature]] varies across the Helix nebula.<ref name="Matsuuraetal2007">{{Cite journal|author=Matsuura, M.|author2=Speck, A. K.|author3=Smith, M. D.|author4=Zijlstra, A. A.|author5=Viti, S.|author6=Lowe, K. T. E.|author7=Redman, M.|author8=Wareing, C. J.|author9=Lagadec, E.|display-authors=4|date=December 2007|title=VLT/near-infrared integral field spectrometer observations of molecular hydrogen lines in the knots of the planetary nebula NGC 7293 (the Helix Nebula)|journal=[[Monthly Notices of the Royal Astronomical Society]]|volume=382|issue=4|pages=1447–1459|arxiv=0709.3065|bibcode=2007MNRAS.382.1447M|doi=10.1111/j.1365-2966.2007.12496.x|s2cid=118514953}}</ref> The rotational-vibrational temperature ranges from |
The [[excitation temperature]] varies across the Helix nebula.<ref name="Matsuuraetal2007">{{Cite journal|author=Matsuura, M.|author2=Speck, A. K.|author3=Smith, M. D.|author4=Zijlstra, A. A.|author5=Viti, S.|author6=Lowe, K. T. E.|author7=Redman, M.|author8=Wareing, C. J.|author9=Lagadec, E.|display-authors=4|date=December 2007|title=VLT/near-infrared integral field spectrometer observations of molecular hydrogen lines in the knots of the planetary nebula NGC 7293 (the Helix Nebula)|journal=[[Monthly Notices of the Royal Astronomical Society]]|volume=382|issue=4|pages=1447–1459|arxiv=0709.3065|bibcode=2007MNRAS.382.1447M|doi=10.1111/j.1365-2966.2007.12496.x|s2cid=118514953}}</ref> The rotational-vibrational temperature ranges from 1,800 [[kelvin|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'.<ref name="Matsuuraetal2007" /> |
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==Videos== |
==Videos== |
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| alt2 = |
| alt2 = |
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| caption2 = 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. |
| caption2 = 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. |
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| image3 = Helix nebula.ogg |
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| width3 = 300 |
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| alt3 = |
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| caption3 = A 3D model of the Helix Nebula from the Galaxy Map app (iOS/Android) |
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}} |
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{{Clear}} |
{{Clear}} |
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| Emission nebula | |
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| Planetary nebula | |
NGC 7293 seen through several visible filters by Hubble Space Telescope
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| Observation data: J2000 epoch | |
| Right ascension | 22h29m 38.55s[1] |
| Declination | −20° 50′ 13.6″[1] |
| Distance | 200±1 pc (650±3) ly |
| Apparent magnitude (V) | +7.6[1] |
| Apparent dimensions (V) | 25′[2] |
| Constellation | Aquarius |
| Physical characteristics | |
| Radius | 2.87 ly (0.88 pc)[2] ly |
| Notable features | One of the nearest PNe |
| Designations | NGC 7293[1] Caldwell63 |
| See also: Lists of nebulae | |
The Helix Nebula (also known as NGC 7293orCaldwell 63) is a planetary nebula (PN) located in the constellation Aquarius. Discovered by Karl Ludwig Harding, most likely 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 Earth's perspective, 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]
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.[2] Spectroscopically, the outer ring's expansion rate is 40 km/s, and about 32 km/s for the inner disk.
The Helix Nebula was the first planetary nebula discovered to contain cometary knots.[12] 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.[13]
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.[14] All tails extend away from the Planetary Nebula Nucleus (PNN) in a radial direction. Excluding the tails, each knot is approximately the size of the Solar System, while each of the cusp knots are optically thick due to Lyc photons from the CS.[2][5][15] There are about 40,000 cometary knots in the Helix Nebula.[16]
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.[17]
The excitation temperature varies across the Helix nebula.[18] The rotational-vibrational temperature ranges from 1,800 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'.[18]
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Stars
Outer space
