Dumbbell Nebula

Dumbbell Nebula

The Dumbbell Nebula (also known as Messier 27, M 27, or NGC 6853) is a planetary nebula (PN) in the constellation Vulpecula, at a distance of about 1360 light years.

This object was the first planetary nebula to be discovered; by Charles Messier in 1764. At its brightness of visual magnitude 7.5 and its diameter of about 8 arcminutes, it is easily visible in binoculars, and a great observing target in amateur telescopes.

Structure

This PN appears to be shaped like an prolate spheroid and is viewed from our perspective along the plane of its equator. In 1992, Moreno-Corral et al. computed that the rate of expansion in the plane of the sky of this PN was no more than 2″.3 per century. From this, an upper limit to the age of 14,600 yr may be determined. In 1970, Bohuski, Smith, & Weedman found an expansion velocity of 31 km/s. Given the semi-minor axis radius of 1.01 ly, this implies that the kinematic age of the PN is 9,800 years old.

Knots

Like many nearby planetary nebulae, the Dumbbell contains knots. Its central region is marked by a pattern of dark and bright cusped knots and their associated dark tails (see picture). The knots vary in appearance from symmetric objects with tails to rather irregular tail-less objects. Similarly to the Helix Nebula and the Eskimo Nebula, the heads of the knots have bright cusps which are local photoionization fronts.

Central star

The central star, a white dwarf, is estimated to have a radius which is 0.055 ± 0.02 R which gives it a size larger than any other known white dwarf. The central star mass was estimated in 1999 by Napiwotzki to be 0.56 ± 0.01 M.

See also

Notes

  1. Radius = distance × sin(angular size / 2) = 1,240 * sin(8′.0 / 2) = 1.44 ly
  2. Semi minor axis = distance × sin(minor axis size / 2) = 1,240 * sin(5′.6 / 2) = 1.01 ly
  3. Kinematic age = semi-minor axis / expansion rate = 1.01 ly / 31 km/s = 9.56 km / 31 km/s = 3.08 s = 9,800 yr
  4. 7.5 apparent magnitude - 5 * (log10(420 pc distance) - 1) = -0.6 absolute magnitude

References

External links

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