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M 27

Vul

• 12 x 300 sec - 1 h

The Dumbbell Nebula (also known as the Dumbbell Nebula, or by its catalog designations M 27 and NGC 6853) is a famous and bright planetary nebula visible in the constellation Vulpecula.

The Dumbbell Nebula is quite easy to locate, lying about three degrees north of the magnitude 3.5 star γ Sagittae; it is easily visible even with 10x50 binoculars and, on very dark and clear nights, even with smaller instruments, such as 8x30. A 114mm telescope can already reveal its main feature, a shape vaguely reminiscent of an hourglass due to the cloud's two large, bright lobes; more powerful instruments, preferably equipped with appropriate filters, allow for a greater degree of detail and nuance. The small central star, at magnitude 13.6, is often used as a test to determine the clarity of a starry night using 200mm telescopes.

The Dumbbell Nebula can be easily observed from both hemispheres of the Earth, thanks to its not excessively northerly declination. From the northern regions, however, it is more visible and appears extremely high in the sky on summer nights, while from the southern hemisphere it remains consistently low, except for areas near the equator. It is, however, visible from all inhabited areas of the Earth. The best time to observe it in the evening sky is between June and November.
The Dumbbell Nebula was first observed by Charles Messier in 1764 and was the first planetary nebula ever discovered. William Herschel, unaware that he was dealing with a nebula, attempted to resolve it into stars. He failed, but the presence of a large number of small stars overlapping in the same field of view led him to believe that with superior instruments he could. His son, John, however, considered it a true nebula. Admiral Smyth described it as an inexplicable, yet marvelous, object. Lord Rosse, however, continued to consider it resolvable into stars, although he too clearly failed in the attempt; he left, along with the Herschels, very accurate drawings of the nebula.
The nebula is approximately 1,360 light-years from Earth, has an apparent magnitude of 7.4, an apparent diameter of approximately 8 arcminutes, and is estimated to be 9,800 years old. Its shape resembles that of a prolate spheroid and is seen along the perspective line of the equatorial plane. In 1992, it was determined that the rate of expansion of this nebula on the sky plane is no greater than 2.3 minutes per century. Consequently, a maximum age limit of approximately 14,600 years can be established. In 1970, the true expansion velocity was calculated to be 31 km/s. Given that the major axis has a radius of 1.01 light-years, the kinematic age of the nebula would be 9,800 years.

As in many other nearby planetary nebulae, knots are easily visible in M27; Its central region is marked by a layer of dark and bright knots, associated with filaments. The knots exhibit a wide range of morphologies, from symmetrical with filamentary tails to asymmetrical with no tails at all. Similar to what was observed in the Helix Nebula and the Eskimo Nebula, the heads of the knots have bright cusps, corresponding to areas of local photoionization fronts.The central star is a white dwarf with a radius of 0.055 ± 0.02 R☉, larger than any other known white dwarf; the mass of the central star was estimated in 1999 at 0.56 ± 0.01 M☉