Anne’s Picture of the Day: The Dumbbell Nebula

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February 24, 2013

The Dumbbell Nebula, a planetary nebula in Vulpecula

Image Credit & Copyright: R. Jay GaBany (http://www.cosmotography.com)

The Dumbbell Nebula (designated Messier 27 or NGC 6853) is a very bright planetary nebula with a radius of about 1.44 light-year, located some 1,360 light-years away in the northern constellation of Vulpecula (the Fox), while it is approaching us at approximately 42 kilometers per second. It is expanding at about 31 kilometers per second.

Despite their name, planetary nebulae have nothing to do with planets. The name of planetary nebulae arose because of the visual similarity between some round planetary nebulae and the planets Uranus and Neptune when viewed through early telescopes.

When a star with a mass up to eight times that of the Sun runs out of fuel at the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot, inner core of the star (collapsing from a red giant to a white dwarf) to radiate strongly, causing this outward-moving cocoon of gas to glow brightly.

Over the next several thousand years, the Dumbbell nebula will gradually disperse into space, and then the white dwarf will cool and fade away for billions of years. Our own Sun is expected to undergo a similar fate, but fortunately this will not occur until some 5 billion years from now.

The Dumbbell nebula is shaped like a somewhat elongated spheroid. But, we happen to see this nebula roughly along its equatorial plane; if it were to be viewed from near one pole, it would probably have the shape of a ring, and perhaps appear similar to the Ring Nebula (M57).

The Dumbbell consists of material that has been ejected from the hot central star, a white dwarf. This white dwarf is estimated to have a radius of about 0.055 that of our Sun which gives it a size larger than any other known white dwarf. Its mass is estimated to be some 0.56 solar masses.

The gas atoms in the nebula are excited (heated) by the intense ultraviolet radiation from this white dwarf and emit strongly at specific wavelengths. Its bluish coloration is released by oxygen atoms while the red hues are emitted by hydrogen.

The Dumbbell shows many knots, but their shapes vary. Some look like fingers pointing at the central star; others are isolated clouds, with or without tails. Their sizes typically range from 17 – 56 billion kilometers (11 – 35 billion miles), which is several times larger than the distance from the Sun to Pluto. Each contains as much mass as three Earths.

The knots are forming at the interface between the hot (ionized) and cool (neutral) portion of the nebula. This area of temperature differentiation moves outward from the central star as the nebula evolves. In the Dumbbell we are seeing the knots soon after this hot gas passed by.

Dense knots of gas and dust seem to be a natural part of the evolution of planetary nebulae. They form in the early stages, and their shape changes as the nebula expands. Similar knots have been discovered in other nearby planetary nebulae that are all part of the same evolutionary scheme, like the Ring Nebula (NGC 6720), the Eskimo Nebula (NGC 2392) and the Retina Nebula (IC 4406). The detection of these knots in all the nearby planetaries indicates that knots may be a feature common in all planetary nebulae.

The Dumbbell is one of the brightest planetary nebulae on the sky, easily visible in binoculars, and a popular observing target in amateur telescopes.

This image was produced with a RCOS half meter telescope, Apogee Ascent A8050 camera and Astrodon E-Series filters.

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