Messier 27, Dumbell- Nebula
The Dumbbell Nebula is a famous planetary nebula in the constellation "Vulpecula" and was discovered in 1764 by Charles Messier and is listed in his famous catalogue at the
27th position.
The apparent brightness of Messier 27 is given as 7.5mag, the apparent size as 8x6 arcminutes, so that the PN can be recognised even in small binoculars as a nebulous spot.
With a declination of +22° it rises to an altitude of 63° in our latitudes - so it can be optimally observed on a clear summer night.
For a long time, the distance to the nebula was subject to great uncertainties, and even with the Hubble Space Telescope HST, one could not get much closer to the solution.
However, this changed with the launch of the astrometry satellite "GAIA", which took measurements over several years and was finally able to pinpoint the distance to
1,280 light years with an uncertainty of +-10 light years. With this new data, it is of course possible to make much more precise statements about the true size of the PN.
The structure of the Dumbbell Nebula is relatively complex. To begin with, the inner (brightest) part appears to be oval in its overall shape. The reason for this is that the
nebula is radiation-limited in the direction of the short axis. This means that the radiation from the central star is not sufficient to stimulate areas of the nebula further out to
glow. In the direction of the long axis, on the other hand, the nebula is material-limited. The diameter of the nebula (without halo) is 2.95 light years. In the outer parts (in the
direction of the short axis), there are many knots and thickenings that contain most of the matter of the PN, whose mass is given as 6.5% of the mass of the sun. The density is
20,000 atoms per cm³, which is still a factor of 5 less than the molecular density in an ultra-high vacuum on Earth. The temperature of the envelope is around 7,000- 10,000
Kelvin. With the help of numerical simulations, it could be shown that the dumbbell shape was caused by a decrease in the stellar wind. In 1974, a very faint halo was also
discovered that surrounds the PN and has a diameter of 5.6 light years, i.e. it extends almost twice as far into space as the bright main body.
From the expansion speed of 31km/s, the age of the dumbbell nebula could be determined to be 10,000 years.
The central star of Messier 27 bears the designation "BD +22°3878" and shines with an apparent brightness of 14mag. The temperature at the surface is about 100,000 Kelvin.
With a mass of 0.56 solar masses it is relatively light, but with a diameter of 77,000 kilometres it is quite large. The ZS has a red dwarf star of spectral class K as a companion
at a distance of 2,450AE (or 0.039 light years).
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Armed with a 20" aperture equipped with an UHC filter, I set out in summer to look for details in the Dumbbell Nebula. The position was quickly found and even in the 9x50 finder
Messier 27 was easily visible. The nebula appears very bright in a 20" telescope, even without a filter, and even the two ears are easy to make out. With an UHC filter, the nebula is a
stunning sight, especially at lower magnifications of 120x, when the nebula seems to float in 3D between the many stars. After admiring the beauty of the nebula for a while,
I increased the magnification and started to observe the details:
Without a filter, quite a lot of stars can be seen in the nebula at 210x. I took a little extra time to map them all. If I have not miscounted, I have seen 16 stars in the nebula. The small
star directly in the centre is the central star with a visual magnitude of 14mag.
With an UHC filter and a magnification of about 210x I then examined the nebular masses more closely. There are indeed some brighter spots in the interior and the ears are clearly
visible on the right and left. The nebular masses that extend beyond the ears can only be seen very faintly, even with 20". On the other hand, a darker cloud, coming from the upper
left, protrudes into the nebula, which I never really noticed before.
Next time I will keep an eye out for the halo of M27. I am curious to see what can be seen of it.
