Thursday, 15 March 2018

NGC4244: A silver needle

Galaxy season's upon us again... that time of the year where the Earth turns away from the galactic plane in the northern hemisphere and more easily shows us the marvels that lay way beyond our Milky Way. Not that far away from us, at merely 14 million light-years' distance, lies a group of galaxies in the small but wonderful constellation of Canes Venatici, the dogs that hunt the great bear. Last year I already talked about the highly irregular "Train Wreck Galaxy", this year I'm taking you to its spectacular neighbour, NGC4244 or better known as the "Silver Needle Galaxy". 

There's no need to explain this nickname because the minute you point your telescope to it, you'll understand where it came from. It's one of those galaxies we see edge-on and for this reason we see it as a long streak with a brighter and wider area at its core. Yet, from the peculiar clumping of stars along its disk scientists conclude that it must have very loose spiral arms.

Sunday, 11 March 2018

IC2177 + RCW2/Gum1: The Seagull

On the border between the constellations of Canis Major and Monoceros flies a giant seagull, which astronomers identify as IC2177. Of course we're not talking about a bird but about an enormous hydrogen cloud in which active star formation takes place. This cloud spreads over such a great distance (3° across, the diameter of 6 full Moons!) and its surface brightness is so low that it can be quite challenging to observe visually. Even with my binoscope under a fairly decent sky, the body and wings of the Seagull Nebula merely appeared slightly brighter than the background. The seagull's "head" on the other hand, was more easy to make out around the bright star HD53367 (the "eye"), including some structures and a dark lane that ran from the nebula's centre towards its eastern rim and in which many people see the seagull's beak. 

The star HD53367 is quite interesting in its own right as it shows an unusual pattern in its spectrum. Scientists classify stars with this sort of pattern as "Be stars", more famous examples of which are Gamma Cassiopeiae and especially Achernar on the southern hemisphere. The reason why these stars emit these strange lines in their spectrum is because they spin so rapidly that they not only become very oblate, but that they also expel so much gaseous matter under the centrifugal force that it forms a disk around the star itself. This disk scatters the light from the star in such a way that its spectrum's altered. 

Lying almost 4,000 light-years away from us, the Seagull Nebula is producing literally hundreds of new stars, many of which illuminated the field of view of my telescope like a Christmas tree.



Thursday, 1 March 2018

NGC2022: Unnamed and underestimated

It amazes me time and time again that some of the most exotic and least-known objects still carry a popular nickname. Take IC418, for example, the Spirograph Nebula. Not that our Spirograph doesn't deserve a nick, much on the contrary since it's such a beautiful object. But then what about NGC2022, the brightest planetary nebula in Orion? It's a very popular nebula but still no-one seems to have found a nice name for it. 

I guess that the reason for this is that it's so small, although far from as small as IC418. In small to medium-sized telescopes NGC2022 appears almost stellar and you need a bit of aperture and especially very high magnifications in order to bring out some detail. At 507x, however, the bright ring of its inner shell stood out brightly against the thin haze of its outer envelope. Inside of the ring I saw strings of matter connecting it to the 16th magnitude central star, surrounded by abundant detail. I even thought to have caught a glimpse of a tiny star that looks as if it lies on the western part of the ring.

Distance estimates are always difficult with nebular objects and our best guess is that this nebula lies about 8,000 light-years away, so more than double the distance to the Spirograph. Yet, NGC2022 dwarfs it in size, indicating that it is far more evolved with its bright inner shell having almost caught up with its outer, which stretches over a light-year across. The extremely hot (surface temperature 108,000°C!) white dwarf whence the nebula originated has probably reached the point of maximum heating, after which it will cool down and extinguish slowly. 

To me, the nebula looked very much like a grape so I'd like to baptise it officially "Grape Nebula". Perhaps you have a better proposal for a nickname? I'm all ears... :-)

Friday, 23 February 2018

NGC1964: More black holes

Galaxies are entities far beyond the power of our little human brains to grasp. Yes, we think that we understand what they are because we see their nucleus and the spiral arms that whirl around it. But do we really realise what it is we're seeing? Do we, for instance, really understand that the billions of stars that make up the Milky Way that spans across the sky only comprises but a small part of our own galaxy? Do we really have any idea what hundreds of billions of stars actually mean? How much is a hundred billion anyway? And given that there are at least a hundred billion galaxies in the visible universe, each containing hundreds of billions of stars, it would be sheer arrogance to state that the Earth lies at the centre of the Universe and that we, tiny humans, are its divine culmination. 

Now point your telescope again to Orion's feet, to the unknown constellation of Lepus, the hare. In my previous post I've shown you an unexpectedly beautiful planetary nebula in that constellation. Now I'd like to show you a distant galaxy there. NGC1964 lies about 65 million light-years away from us. That's not exceptionally distant since our universe has a radius of over 13 billion light-years, but still, the light of this galaxy started its voyage to Earth around the time that the asteroid, which caused the extinction of the dinosaurs, hit us. So that's a considerable distance. The thing that struck me at first glance, was that this galaxy has a very bright, almost stellar-like core. It immediately reminded me of M77, a galaxy which has a particularly big black hole in its nucleus. The strange thing about black holes is that they're not really black as seen from Earth, but as a matter of fact they're very bright. That's because matter clumps together around it, pulled in by its enormous gravitational force, and becomes extremely dense and hot. So when you see a galaxy with a core like this, rest assured that it contains a super-massive black hole!

Tuesday, 20 February 2018

IC418: The Spirograph

There's so much unknown beauty up there that it never ceases to amaze me. In the dark constellation of Lepus, the hare, at the feet of mighty Orion, you'll find this little bugger. It's obviously a planetary nebula, and one that listens to the denominator IC418, but more commonly known as the Spirograph Nebula. It's nick refers to its complex, almost mathematical structure. 

Experts among you will already have guessed that this nebula's still quite young, hardly 2,600 years old, and in full expansion. Though very small in spite of its relatively close distance of 3,600 light-years, you'll quickly notice some extraordinary details if conditions allow you to push telescope power. Its bright outer shell, gas that was expelled when the star was still in its red giant phase, shines brightly under the heat of the brilliant white dwarf in its heart. The inner shell, on the other hand, appeared much brighter still and seemed to sparkle in the atmospheric turbulences of our Earth. This inner shell is the dying star's atmosphere that was blown away into space after nuclear fusion had become critically unstable. Soon the inner shell will expand so quickly that it'll catch up with the much slower outer envelope, possibly even break through it in order to form ansae, like the ones of the Saturn Nebula

So keep your eye on this one because it still has a lot in store for us in the near future... er... in the next couple of thousand years. 

Thursday, 15 February 2018

Berkeley 21: The edge of our galaxy

Loyal readers of my blog know that I'm obsessed with faint fuzzies... objects so difficult to see that you sometimes wonder whether what you see is real or whether you've entered the realm of science fiction. But perhaps the objects that fascinate me more than anything else are extremely remote (and therefore faint) open clusters. Last year already I took you to Berkeley 19, a cluster that lies even beyond the outermost spiral arm of our galaxy. Today, I'd like to take you just a little bit closer, to a distance of merely 16,000 light-years, right in the heart of this outermost spiral arm. There lies this old star cluster, denominated Berkeley 21, the light of which is nearly completely extinguished by the interstellar dust of the broad Perseus spiral arm which lies between the outer arm and our own. In other words, prepare for something very difficult to see. 

At 104x, I only got a hunch of a fuzzy patch... the suspicion that I had nailed it. It was not until I pushed telescope power to 285x that the cluster revealed itself and at 507x most of its stars could be resolved, albeit with great difficulty. For your information, the brighter stars you see on my sketch all lie a lot closer to us!

Star clusters in that extremely remote part of our galaxy are usually very old because the gravitational influence of the galaxy is a lot less and interstellar matter's not stirred up as much. So don't expect a lot of spectacular star formation there. And if eventually a star cluster does form, it stands a much better chance of remaining compact. Berkeley 21 therefore could be many billions of years old, perhaps even be as old as our galaxy itself.

Monday, 12 February 2018

NGC2129: Others taking the credit

How many times have I already argued that appearances can be so deceiving when observing the night's sky? Sirius shines so brightly that you'd easily think it must be the biggest star out there, but then you realise it only lies 8 light-years away from us. Deneb, the brightest star in Cygnus, looks a lot fainter than Sirius from our perspective, but radiates no less than 200,000 (!) solar luminosities at us from its 1,400 light-year distance. 

Now look at this lovely open cluster, NGC2129, which you'll find on the border between Gemini and Taurus. It's an easy target even for binoculars and that's mainly due to the two bright stars at its centre. Now what if I told you that in reality these two stars aren't even remotely close to the cluster and that they only appear to be part of it from our perspective? Indeed, the brightest of the two (HD250290) is an ordinary, 3 solar mass yellow giant, which lies 1,800 light-years away. Its fainter "sister" that lies slightly below (HD250289) is a similar yellow giant but it lies at a distance of 2,700 light-years. And the rest of the cluster? Well, you'd have to travel three times as far, 7,200 light-years to be precise. So those two bright stars have nothing to do with it whatsoever, nor are they related to each other. They just happen to float in front of this lovely, remote cluster which contains about three dozen stars and which is slowly breaking up under the gravitational force of our galaxy.