Helix Nebula

Source: Wikipedia, the free encyclopedia.
Helix Nebula, NGC 7293
J2000 epoch
Right ascension22h 29m 38.55s[1]
Declination−20° 50′ 13.6″[1]
Distance200±pc (650±3ly
Apparent magnitude (V)+7.6[1]
Apparent dimensions (V)25′[2]
ConstellationAquarius
Physical characteristics
Radius2.87 ly (0.88 pc)[2] ly
Notable featuresOne of the nearest PNe
DesignationsNGC 7293[1] Caldwell 63
See also: Lists of nebulae

The Helix Nebula (also known as NGC 7293 or Caldwell 63) is a

General information

The Helix Nebula is an example of a

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 location of NGC 7293 (labelled in red)

The Helix Nebula is thought to be shaped like a

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

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

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

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

References

  1. ^ a b c d "NGC 7293". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-12-07.
  2. ^
    S2CID 119507454
    .
  3. .
  4. ^ "SIMBAD references".
  5. ^ .
  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. .
  10. .
  11. .
  12. ^ "APOD: 2008 April 13 - Curious Cometary Knots in the Helix Nebula". apod.nasa.gov. Archived from the original on 2012-05-05.
  13. .
  14. .
  15. .
  16. .
  17. . Retrieved 22 November 2020.
  18. ^ .

External links