History

Messier 27 or the Dumbbell Nebula is probably the most striking planetary nebula in the northern starry sky. It was discovered by Charles Messier on 12^th July 1764. He wrote about it: «Nebula without a star, discovered in the Fox, between the two front legs, and very close to the 14th star of this constellation, 5th magnitude according to Flamsteed; it can be clearly seen with an ordinary telescope of 3 and a half feet: it appears in an oval shape, and contains no stars.» ^[281] T. W. Webb compared the nebula to a dumbbell because the shape of the nebula reminded him of two connected masses. ^[4]

Physical Properties

The large apparent diameter of the PN suggests that it is relatively close to us. The calculated distances vary from 300 to 1250 light years. If one assumes that the nebula is at a distance of close to 900 light years, M 27 would be one of the largest PNs of this type with a true diameter of almost 2.5 light years. The expansion speed of M 27 found by spectroscopic analysis is around 27.3 km/s. According to measurements on astrometric photographs, the nebula grows at about 1 arc seconds per century, according to other sources it is even 7 arc seconds. If one assumes that the rate of expansion is relatively constant, one arrives at an age of the nebula of about 48'000 years, about two and a half times the average age of a typical bright planetary nebula. According to other measurements, it is 20'000 years old. M 27 consists of about 92% hydrogen, 7% helium and traces of oxygen, nitrogen, neon, sulfur and argon. These gases shine in specific wavelengths, M 27 shines very strongly on the O-III line of double ionized oxygen. Around the bright nebula, which is about 5.8 arc minutes in diameter, there is still a faint halo 15.2 arc minutes in diameter.

The central star is about 13.8 mag bright and would have about half the luminosity of the sun at the distance. As in all planetary nebulae, er is an abnormal, hot blue dwarf or sub-dwarf with the spectrum resembling that of a past nova. The calculated surface temperature is around 85'000 Kelvin. K. M. Cudworth of Yerkes Observatory noted that the central star may be a physical binary star. The companion is a yellowish star 17. Magnitude, about 6.5 arc seconds in the direction of 214° from the main star. With the previously assumed distance, the two stars are about 1800 AU apart and have the absolute magnitudes of +6.2 mag and +9.7 mag. The The first shows a fairly continuous spectrum and stimulates the nebula to glow with its strong UV radiation. ^[4]