Friday 25 May 2018

NGC3242: Jupiter's Ghost

Low on the horizon, for northern observers, during the early spring months... in an otherwise seemingly empty part of the sky you may stumble upon this big and bright planetary nebula. It's popular name "Jupiter's Ghost" refers to its similar apparent size and shape compared to the biggest planet of our solar system. In reality this nebula is some two light-years across and is still in full expansion. It merely appears the size of Jupiter because it is 1,400 light-years away.

The bright inner halo, the central star's dying breath, was blown into space some 1,500 years ago and is now rapidly catching up with the large outer shell which gradually built up during the final phase of the star's life. It's central star of 11th magnitude was not that easy to see, although it's radiating at over 150,000°C and lighting up the gas bubble around it. The gas is heated up to the extent that it begins to ionise and emit a bluish-green light of its own. Actually, we're catching this nebula right at its brightest phase. Within the next couple of thousand years it will expand further, fade and eventually dissolve into space.

Thursday 17 May 2018

NGC5005: Black holes lead to star formation?

Yes, I know, it's a bit of a strange title for this post. Let's have a close look at NGC5005, a galaxy that's not in our immediate vicinity (estimates vary greatly from 45 to 113 million light-years, with an average of 65). It's a fairly bright galaxy in Canes Venatici, the hunting dogs, which can be seen quite easily with a modest telescope. 

Through the binos at 285x, it revealed a wonderful amount of detail, such as the darker arc on the left. But what we're really interested in, is its nucleus. Spectroscopic analysis revealed that the heart of this galaxy contains a lot of non or weakly ionised atoms, such as O, O+, N+, and S+. Scientists classify galaxies with such a cloud of weak ions in their core LINERs, which stands for "Low-Ionisation Nuclear Emission". This is nothing unusual and as it appears up to a third of all galaxies could fall under this category. The question however, is what causes this enormous cloud, which may swirl inward up to 750km/s! Scientists are still heavily debating on that, but significant x-ray emissions in the case of NGC5005 seem to confirm a super-massive black hole in its centre. Another observation that we make, is that this ion cloud produces some serious star formation. Usually not a lot of stars are formed in the nucleus of a galaxy, which therefore contains an older star population, and most starburst activity is generally concentrated in billowing spiral arms. 

So may we conclude that a black hole can be so powerful as to cloak itself with a cloud of ionised gas in which thousands of new stars are born? 

Thursday 3 May 2018

Frosty Leo... again

I've already written about this highly unusual planetary nebula in construction two years ago and will repeat most of this post here, to give you some background information on IRAS 09371 + 1212, or in other words "Frosty Leo". 

When I made my first observation, I was unfortunately limited to 200x, which is far from sufficient if you want to see some detail in this tiny puff of mostly water crystals. So here's my recent observation with the binoscope and... yes... at 507x details were abundant!

Nature is ruthless. It gives life and make stars sparkle so brightly in our sky that uncountable poets have dedicated their most beautiful work to them. But unfortunately, all beauty must fade and everything that has a beginning also has an end. Even so the seemingly perpetual stars which eventually have to die too. I've repeatedly written about dying stars, either the ones that go fairly quietly through the formation of a planetary nebula, or the ones that grant us the unforgettable spectacle of a supernova explosion. Today, I'd like to show you a star that's literally exhaling its dying breath. We're talking about a so-called protoplanetary nebula, nicknamed "Frosty Leo", and this nickname isn't far-fetched at all as I shall explain. 

When a small to medium-sized star reaches the end of its life cycle, it runs out of fuel to sustain nuclear fusion and becomes highly unstable. Its interior collapses and the shock wave that this causes literally blows the star's atmosphere into space, where it will form large gaseous shells or "bubbles" around the remains of the star. The contraction of the dying star's core will in turn generate so much heat that it will reignite fusion of helium into heavier elements, such as carbon, oxygen and even iron. The star's radiation continues to blow up the "bubble", which eventually dissipates into space, and heat it up to a point where the gas ions start to emit light as well. This is what we call a "planetary nebula". 

In the case of Frosty Leo, however, we're not quite there yet. We're actually witnessing the collapse of the star and the initial expulsion of its atmosphere. Its last breath, as a matter of speaking. At this low magnification it's almost impossible to see, but the star's atmosphere is blown away in two opposite lobes which keep expanding at a rate of a whopping 25km/s. Remember that in order to escape from Earth's gravity a rocket needs an initial velocity of 11,2km/s or 33 times the speed of sound, so imagine how fast the nebula around Frosty Leo is forming!

As I said, the nickname wasn't chosen by chance or after a very successful party because its discoverers had to celebrate their findings. No, the nickname derives from the fact that the nebula consists for a large part of... water-ice grains! Plus of course that it resides in Leo. For the time being it's perhaps the only such nebula that we know of, so this makes it doubly interesting. Another weird fact is that it lies 10,000 light-years away from us and an unusual 3,000 light-years above the galactic plane. Therefore it must have been a very lonely star, condemned to die in complete isolation.

In the next millennia Frosty Leo will keep expanding and eventually the nebula, which currently only reflects the light from the star, will light up, adding another Crystal Ball or Eskimo to our skies. But let's not be impatient. This object is already a great spectacle and much more so from a scientific standpoint.