The
Dumbbell Nebula (also known as the
Apple Core Nebula,
Messier 27, and
NGC 6853) is a
planetary nebula (nebulosity surrounding a white dwarf) in the
constellationVulpecula, at a distance of about 1360
light-years.
[1] It was the first such nebula to be discovered, by
Charles Messier in 1764. At its brightness of
visual magnitude 7.5 and diameter of about 8
arcminutes, it is easily visible in binoculars
[6] and is a popular observing target in
amateur telescopes.
The Dumbbell Nebula appears shaped like a
prolate spheroid and is viewed from our perspective along the plane of its equator. In 1992, Moreno-Corral
et al. computed that its rate of expansion angularly was, viewed from our distance, no more than 2.3
arcseconds (″) per century. From this, an upper limit to the age of 14,600 years may be determined. In 1970, Bohuski, Smith, and Weedman found an expansion velocity of 31
km/s. Given its
semi-minor axis radius of 1.01
ly, this implies that the kinematic age of the nebula is 9,800 years.
[5][7]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.
[7]The central star, a
white dwarf progenitor, is estimated to have a radius which is 0.055±0.02
R☉ (0.13 light seconds) which gives it a size larger than most other known white dwarfs.
[2] Its mass was estimated in 1999 by Napiwotzki to be 0.56±0.01
M☉.
[2]The Dumbbell nebula can be easily seen in binoculars in a dark sky, just above the small constellation of
Sagitta.
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