Sunday 18 September 2016

The ring is fake... and a little surprise...

The most famous of all planetary nebula is probably the object that Charles Messier catalogued as number 57 back in 1779, more commonly known as the Ring Nebula. A small telescope will already reveal the doughnut shape consisting of ionised gas that's being expelled by what once was a star slightly bigger than our Sun. Some 7.000 years ago this star ran out of fuel and began to die slowly, ejecting its atmosphere into space whereas the star's hot nucleus will cool down and extinguish over the next billions of years. It was actually the first time that I managed to see this particular central star with my own eyes. Being of the 15th magnitude, the star isn't that impossible to see through a telescope as such, but the still fairly bright nebulosity in the "hole" of the doughnut tends to hide it. The ring itself's currently reached a diameter of almost 1 lightyear and is expanding at a rate of 20 to 30 km/s, some 70.000 to 100.000 km/h! Comparing old photographs to recent ones, the difference in size's quite noticeable! The nebula's also headed straight towards us, but being at a distance of 2.000 lightyears it would need more than 21 million years to reach us, by which time it will have dissolved completely.

The most recent observations with the Hubble space telescope revealed an even bigger surprise. The Ring Nebula's not a doughnut at all, but it's a cylinder! Astronomers didn't notice it at first because we see the cylinder end-on, as you'd look through the hole of a roll of toilet paper. The Hubble's high resolution snapshots, however, clearly showed clouds of dust flowing out of the central star which are silhouetted against the outer portions of the ring. Such barrel or hourglass shapes are not uncommon at all among planetary nebulae. Thick layers of gas and dust around the waist of the star often slow down the expansion in that direction, leaving the gas free to flow out from the poles. 

But there's more to see in my sketch apart from this spectacular nebula and I intentionally didn't place it at the centre. On the right and slightly up you may see a small, fuzzy patch, even with a sort of irregular shape. This is a galaxy, a bit smaller than our Milky Way, which lies at the incredible distance of 230 million lightyears! It's of the barred spiral type, which means that the spiral arms do not originate from the core itself, but that there's a bar-like structure that goes through the core. The spiral arms originate from the outer edges of that bar. Obviously this is all but impossible to see on my sketch. This little galaxy's so remote that you can't even see its nucleus unless you've got a sizeable telescope and an almost perfect sky. So you can imagine how happy I was that I could still make out some structure in it.   


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