Helix Nebula

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Helix Nebula, NGC 7293
Emission nebula
Planetary nebula
NGC7293 (2004).jpg
NGC 7293 seen through several visible filters by Hubble Space Telescope
Observation data: J2000 epoch
Right ascension 22h 29m 38.55s [1]
Declination −20° 50′ 13.6″ [1]
Distance200±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 featuresOne of the nearest PNe
Designations NGC 7293 [1] Caldwell 63
See also: Lists of nebulae

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, 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]

Contents

General information

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]

Structure

A 3 dimensional map of carbon monoxide in NGC 7293 Helix3D.png
A 3 dimensional map of carbon monoxide in NGC 7293
Structure and cometary knots are prominent in this Infrared false-color image taken by the Spitzer Space Telescope Comets Kick up Dust in Helix Nebula (PIA09178).jpg
Structure and cometary knots are prominent in this Infrared false-color image taken by the Spitzer Space Telescope
The location of NGC 7293 (labelled in red) NGC7293Location.png
The location of NGC 7293 (labelled in red)

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.

Knots

A closer view of knots in the nebula Close-Up of the Helix Nebula.jpg
A closer view of knots in the nebula

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 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'. [18]

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.
A 3D model of the Helix Nebula from the Galaxy Map app (iOS/Android)

See also

Related Research Articles

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<span class="mw-page-title-main">H II region</span> Large, low-density interstellar cloud of partially ionized gas

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<span class="mw-page-title-main">Vulpecula</span> Constellation in the northern celestial hemisphere

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<span class="mw-page-title-main">Proplyd</span> Dust ring surrounding large stars thousands of solar radii wide

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<span class="mw-page-title-main">Cat's Eye Nebula</span> Planetary nebula in the constellation Draco

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<span class="mw-page-title-main">Dumbbell Nebula</span> Planetary nebula in the constellation Vulpecula

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<span class="mw-page-title-main">Eskimo Nebula</span> Planetary nebula in the constellation Gemini

The Eskimo Nebula, also known as the Clown-faced Nebula, Lion Nebula, or Caldwell 39, is a bipolar double-shell planetary nebula (PN). It was discovered by astronomer William Herschel in 1787. The formation resembles a person's head surrounded by a parka hood. It is surrounded by gas that composed the outer layers of a Sun-like star. The visible inner filaments are ejected by a strong wind of particles from the central star. The outer disk contains unusual, light-year-long filaments.

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<span class="mw-page-title-main">Owl Nebula</span> Planetary nebula in the constellation Ursa Major

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<span class="mw-page-title-main">NGC 7027</span> Planetary nebula in the constellation Cygnus

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<span class="mw-page-title-main">Sh2-279</span> Emission nebula in the constellation Orion

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<span class="mw-page-title-main">IC 4406</span> Planetary nebula in the constellation of Lupus

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<span class="mw-page-title-main">NGC 5882</span> Small planetary nebula in the constellation Lupus

NGC 5882 is a small planetary nebula in the southern constellation of Lupus, positioned about 1.5° to the southwest of the star Epsilon Lupi. It was discovered by English astronomer John Herschel on July 2, 1834 from the Cape of Good Hope observatory. John L. E. Dreyer described it as "very small, round, quite sharp". It is located at a distance of approximately 7.7 kilolight-years from the Sun.

<span class="mw-page-title-main">NGC 5307</span> Planetary nebula in the constellation Centaurus

NGC 5307 is a planetary nebula in the southern constellation of Centaurus, positioned less than 3° to the northeast of the star Epsilon Centauri. It was discovered by English astronomer John Herschel on April 15, 1836. The nebula is located at a distance of approximately 10.6 kilolight-years from the Sun. The central star, designated PNG 312.3+10.5, is a weak emission-line star, superficially similar to the WC subtype of Wolf–Rayet stars. It has a spectral class of O(H)3.5 V.

<span class="mw-page-title-main">NGC 7354</span> Planetary nebula in the constellation Cepheus

NGC 7354 is a planetary nebula located in the northern circumpolar constellation of Cepheus, at a distance of approximately 5.5 kly from the Sun. It was discovered by German-born astronomer William Herschel on November 3, 1787. John L. E. Dreyer described it as, "a planetary nebula, bright, small, round, pretty gradually a very little brighter middle".

<span class="mw-page-title-main">NGC 6884</span> Planetary nebula in the constellation in the constellation Cygnus

NGC 6884 is a planetary nebula located in the constellation Cygnus, less than a degree to the southwest of the star Ο1 Cygni. It lies at a distance of approximately 12.5 kly from the Sun. The nebula was discovered on May 8, 1883, by American astronomer Edward C. Pickering.

<span class="mw-page-title-main">Cometary knot</span> Structure in some planetary nebulae

Cometary knots, also referred as globules, are structures observed in several nearby planetary nebulae (PNe), including the Helix Nebula, the Ring Nebula, the Dumbbell Nebula, the Eskimo Nebula, and the Retina Nebula. They are believed to be a common feature of the evolution of planetary nebulae, but can only be resolved in the nearest examples. They are generally larger than the size of the Solar System, with masses of around 0.00001 times the mass of the Sun, which is comparable to the mass of the Earth. There are about 40,000 cometary knots in the Helix Nebula.

<span class="mw-page-title-main">NGC 6445</span> Planetary nebula in the constellation Sagittarius

NGC 6445, also known as the Little Gem Nebula or Box Nebula, is a planetary nebula in the constellation Sagittarius. It was discovered by William Herschel on May 28, 1786. The distance of NGC 6445 is estimated to be slightly more than 1,000 parsecs based on the parallax measured by Gaia, which was measured at 0.9740±0.3151 mas.

References

  1. 1 2 3 4 "NGC 7293". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2006-12-07.
  2. 1 2 3 4 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.
  3. ↑ 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.
  4. ↑ "SIMBAD references".
  5. 1 2 3 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 .
  6. ↑ "Urban Legends Reference Pages". The Eye of God. 5 February 2004. Retrieved 2007-07-16.
  7. ↑ "The Eye of Sauron (aka NGC7293)". Sky and Telescope.
  8. ↑ Nancy Atkinson (4 October 2012). "Eye-Like Helix Nebula Turns Blue in New Image". Universe Today. Archived from the original on 14 July 2014.
  9. ↑ 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 .
  10. ↑ 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.
  11. ↑ 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.
  12. ↑ "APOD: 2008 April 13 - Curious Cometary Knots in the Helix Nebula". apod.nasa.gov. Archived from the original on 2012-05-05.
  13. ↑ 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 .
  14. ↑ 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.
  15. ↑ O'Dell, C. R.; Balick, B.; Hajian, A. R.; Henney, W. J.; et al. (2003). "Knots in Planetary Nebulae". In Arthur, Jane; Henney, William (eds.). Winds, Bubbles, and Explosions: A Conference to Honor John Dyson, Pátzcuaro, Michoacán, México, September 9–13, 2002. Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias. Vol. 15. Instituto de Astronomía, Universidad Nacional Autónoma de México. pp. 29–33. Bibcode:2003RMxAC..15...29O.
  16. ↑ 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.
  17. ↑ 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.
  18. 1 2 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.
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