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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, 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 some
9,800 years.[4][5]
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.[2]
The central star mass was estimated in 1999 by Napiwotzki to be 0.56
± 0.01 M☉.[2]
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