The Dumbbell Nebula appears shaped like aprolate spheroid and is viewed from our perspective along the plane of its equator. In 1992, Moreno-Corralet al. computed that its rate of expansion angularly was, viewed from our distance, no more than2.3 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 of31 km/s. Given itssemi-minor axis radius of1.01 ly, this implies that the kinematic age of the nebula is 9,800 years.[3][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 theHelix Nebula and theEskimo Nebula, the heads of the knots have bright cusps which are localphotoionization fronts.[5]
The central star, awhite dwarf progenitor, is estimated to have a radius which is0.055±0.02 R☉ (0.13 light seconds) which gives it a size larger than most other known white dwarfs.[6] Its mass was estimated in 1999 by Napiwotzki to be0.56±0.01 M☉.[6]
^abO'dell, C. R.; Balick, B.; Hajian, A. R.; Henney, W. J.; et al. (2003). "Knots in Planetary Nebulae".Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias.15:29–33.Bibcode:2003RMxAC..15...29O.
