Wednesday 10 August 2016

The Blue Flash

NGC6905 is a wonderful planetary nebula in the small but remarkable constellation of Delphinus. Loyal readers of my blog will already have guessed that this nebula is what's left of a dying normal-sized star. The star's nucleus still survives and has turned into an extremely hot white dwarf star with a surface temperature around 150.000°C. In comparison, the temperature on our Sun's surface is only 5.500°C. A white dwarf's a very peculiar kind of star because its size is comparable to that of the Earth whereas its mass is not much different to our Sun's. Needless to say that it's extremely dense and "heavy". Unlike a normal star, no nuclear fusion takes place in it anymore; it's light and energy emission being solely the result of the remaining heat of what was once an active nuclear fusion reactor. With time, this star will therefore slowly cool down and fade until all that's left is a ball of mainly carbon. This cooling process takes a lot of time, many billions of years, and therefore there aren't such carbon balls or "black dwarves" around yet because the universe simply isn't old enough. 

This particular white dwarf was clearly visible in my binoscope. But perhaps more interesting for visual astronomers, the star's atmosphere was expelled into space and now forms a rapidly expanding bubble of gas filaments around the white dwarf. Also these filaments were more than evident in the binoscope at a magnification of 285x. Actually, I was amazed at the amount of detail that I was able to make out. This planetary also has two extremely faint "wings" just above and below the main nebula on this sketch. These were difficult to see and I've tried to represent just that. Some people therefore call it a mini-Dumbbell nebula because it does look a bit like a smaller and fainter version of the famous nebula in Vulpecula. 

The "Blue Flash" however lies a lot further away from us: 7.500 lightyears compared to 1.300 for the Dumbbell. But I hope that my sketch will encourage you to visit this fainter and more distant planetary as well because it really deserves it.   

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