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M27 - The Dumbbell Nebula by Dave Smith

Dave says " This is my second guided image. It was taken through a Vixen FL102S refracting telescope 4 inches/102mm diameter) with a Canon 40D DSLR camera at prime focus. The guiding was using a Skywatcher ST80 telescope, mounted side by side with the Vixen, and a DMK21 camera using the PHD guiding software. Each sub exposure was for 5 minutes with a total exposure time of 75 minutes. The subs together with dark frames, bias frames and flats were combined in Deep Sky Stacker and the resulting file processed in Photoshop CS2."

This image was published in the Sky at Night Magazine Hotshots disc November 2010.

You can see more of Dave Smith's images on his website by going to our Links page.

The Dumbbell is just one of many examples of a class of object known as planetary nebulae. An important point regarding this is that they have absolutely nothing to do with planets. The term comes from the fact that a number of examples are somewhat planet-like in appearance.

They are actually a gaseous cloud surrounding a star that has either died in the comparatively recent past, or which is in the final stages of dying. Stars that come to the end of their lives still in possession of more than about eight to ten solar masses of material undergo a catastrophic Type II supernova explosion that blows the star to smithereens. However, lower mass stars end their lives in a less dramatic fashion. They go through a number of cycles during each of which they puff off a shell of gas from their outer layers in a far more sedate fashion than is the case with a supernova explosion. Whereas super nova explosions disperse the fabric of their progenitor stars at velocities of some thousands of kilometres per second, the rate for planetary nebulae is more like a few tens of kilometres per second.

Eventually, having shed a number of concentric shells of gas in this way, the astoundingly hot region close to what had for so much of the star’s life been its thermo nuclear core becomes exposed. The intense radiation from the exposed, or almost exposed, core excites the atoms of gas in the receding gas shells, with the result that many of the gas atoms become ionised – that is to say they lose one or more of their electrons – as they absorb the intense radiation from what remains of the dying central star. As some atoms become ionized, others undergo de ionisation; in other words they recapture previously lost electrons. As they do so they must give up the energy they absorbed during ionisation. This energy is given up by emitting photons of light with very specific wavelengths. It is this light that we see as a nebulous glow in the sky. The wavelengths emitted are so specific that the particular gas and its ionisation state (i.e. the number of electrons it has lost) can be positively identified. A good deal of other information can also be gleaned about the nature of the central star and the conditions within the nebula.

Gases such as oxygen and nitrogen, which are so important for life here on Earth, are regularly found to be responsible for the luminous emission from planetary nebulae.

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