Monday, 29 May 2017

A tiny footprint

I've already taken you off the beaten path many times before and this time I'd like to take you waaaaay off it. Minkowsi 1-92 (or M1-92 for intimate friends) is a very interesting nebula that can be found near Albireo, the eye of Cygnus, the swan. With its 11,5 magnitude it should be accessible to most astronomy enthusiasts. The thing is that whereas most of them will indeed see it, very few will actually be able to recognise it. The reason for that is that M1-92's... incredibly tiny. I had to push my binoscope to 507x in order to see some detail because even at 285x I could've mistaken it for an ordinary star. 

M1-92, aka the "Footprint Nebula", is not a planetary nebula, or not yet anyway. It's a proto-planetary, just like Frosty Leo. We're actually witnessing the death of a star here! Nuclear fusion's become critically unstable and the star collapses under its own gravity, expelling its atmosphere in the shockwave caused by the collapse. Surprisingly this doesn't happen like a balloon that's blown up. As the atmosphere around the star's equator is usually a lot thicker due to the star's rotation, the gases escape more easily around the poles and form inverted umbrella-shaped lobes. Around the equator of this particular star also lies a large dust disk that inhibits the gas from escaping even more: it looks like a waist in between the two lobes of gas. The lower lobe appears brighter because it's pointing somewhat in our direction, whereas some of the light of the upper lobe's blocked by the equatorial dust disk. In a few thousand years the tremendous heat of the dying nucleus (Currently 20,000°C on its surface that will increase to over 100,000°C as the atmosphere evaporates) will fry the expelled gas shell up to the point that it'll ionise and start to emit light. In other words, our nebula will begin to look something like this. Also in this example you can clearly see that the gas was not expelled uniformly and you can even notice some plumes of gas ("ansae") that have broken through the outer shell, blown out by the strong polar winds. 

Currently our Footprint Nebula's expanding at 50km/s but given its 10,000 lightyear distance it will still take a bit of time before we'll be able to see some real change with ordinary telescopes. In the meantime, it'll remain a challenge for deep-sky fanatics. :-) 

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