Tuesday, 31 January 2017

A galaxy with a black eye

I've never been very fond of galaxies. Yes, there are some really nice ones such as M51, the famous Whirlpool, or M82, the Cigar Galaxy, without even mentioning Andromeda. But in the end, most galaxies appeared to me as amorphous, faint blobs lacking the details that could make them interesting. Perhaps I should've looked a little better, but in general I loved nebulae a thousand times more. At least these always showed me some remarkable details, frail filaments or internal structures. 

In comes the 18" binoscope and now things have changed. As you can see on my sketches, even very faint and distant galaxies have taken form and character. Sometimes, galaxies now reveal the scars of such cataclisms as we with our small human minds couldn't possibly imagine. I've talked about galaxies being torn apart by another galaxy zooming by such as the Tadpole or the galactic tango of NGC627 and IC1727 (see the video here). I've also already talked about galaxies crashing into other galaxies, such as the Flying Ghost. But in the end, the universe continues to be and even the scariest of scars will heal with time. The Tadpole's long trail of stars and matter will break off and probably form a new mini-galaxy of its own. The two wild tangoers will eventually regroup their stars and in a few billion years no-one will still be able to recognise a flying ghost in the seemingly normal, albeit enlarged NGC520.

And yet, that's not entirely true. Sometimes these scars will not heal completely. Take a small telescope and point it at M64, one of the finest galaxies in spring sky. You will notice that there's a dark patch under the bright nucleus, hence the nickname "Black Eye Galaxy". The larger the telescope, the more prominent this dark patch becomes and with my binoscope I saw it like on the sketch below. It even gave a sort of 3D-sensation to the galaxy's central part as if I was looking at a lunar crater! These enormous dark clouds of dust around the nucleus are caused by a strange phenomenon: the outer 40.000 lightyears of this galaxy are rotating in the opposite direction of the inner 3.000! The friction that this counterrotation causes at the separation point is generating thick clouds of swirling matter and... violent star formation! Now you might wonder... what the heck caused the outer part of a galaxy to counterrotate the inner part? The most likely explanation seems to be that billions of years ago another galaxy collided with it in the opposite direction of its rotation and was eventually absorbed. Perhaps one day the rotation of the large outer region will slow down, come to a halt and will then obey the galaxy's gravitational centre which tells it to rotate in the same direction as the nucleus. But for the time being it's still going its own way and the black eye's the proof that this galaxy's received a pretty hard blow to the head.  


Friday, 27 January 2017

Destiny is not an absolute

Yes, I know, this blog post has an awkward title. So what am I talking about here? Look at this older sketch that I made of the bright open cluster M35 in Gemini:

It's a treat, isn't it? Just look at those dozens of twinkling stars that under a really dark sky are already visible to the naked eye. Obviously you've also noticed that faint little blob, just below the drawing's centre. Now let's zoom into that with the binoscope:


It's another star cluster, called NGC2158. Is it related to big and bright M35, you might wonder? No, not at all! As I explained in my previous blog post appearances may deceive! M35 lies 2.800 lightyears away from us; to reach NGC2158 you'd have to travel 11.000 lightyears! All right, you might already have guessed that from the first sketch. But there's more! M35 is a typical middle-aged cluster, some 100 million years old, that is now slowly breaking up under the gravitational pull of our galaxy. Soon all of these bright and young stars will go their own way. NGC2158 on the other hand is surprisingly old for an open star cluster, it's age being estimated at 2 billion years! So why hasn't this cluster broken up as well? Isn't the force of gravity an absolute? Yes, of course it is. But first of all, NGC2158's much further away from our galaxy's gravitational centre and therefore it is influenced less by it. What's more, NGC2158's an extremely rich and compact cluster. Even at 285x with my gigantic telescope I wasn't able to resolve all the stars within it. Well, I could have taken the telescope to 500x and then perhaps I would have resolved more stars, but I liked the view as it was. So many stars packed together in such a confined space, means that their mutual gravitational pull outweighs the gravitational pull of our galaxy and therefore they've managed to stay together for such a long time. Many stars in this cluster have already come of age and some have even evolved into red giants, as opposed to the young, blue stars in M35. 

So you see, sometimes an unavoidable destiny can be avoided.

Wednesday, 25 January 2017

Appearances may deceive

When I was observing the remote open cluster NGC1193, I turned my telescope to this nearby couple of galaxies, which listen to the names NGC1160 (on the left) and NGC1161 (on the right). Not that they are that extraordinary to look at. NGC1160 definitely looked fainter than it's bigger sister, although I was able to make out a dark lane near its southwestern border (top left on my sketch). NGC1161 showed a bright and compact nucleus and a faint, regular spiral structure. It's obvious that the latter is the dominant galaxy of the two and its smaller companion looked a bit irregular and even distorted to me, as if it's being cannibalised by the other. 

Now here comes the surprise: they're no couple at all. In fact, they're nowhere near to each other and the brighter galaxy actually lies much further away from us! NGC1160 lies at a distance of 78 million lightyears, whereas big NGC1161's 102 million lightyears away. In other words, the distance between the two's ten times the distance between Earth and the Andromeda galaxy! 

Both galaxies are receding from us at incredible speeds, but nearby NGC1160's surprisingly faster. "Hey! Wait for me!" It's moving away from us at a speed of 2.500km per second (!) whereas big NGC1161 is doing only 1.950km per second. So perhaps... some time the little one may catch up with the bigger one after all. 

Friday, 20 January 2017

Birds leaving the nest

Stars are usually born together. They're brought forth by giant hydrogen clouds that contract under their own gravity into dense spheres; so dense that they light up and start nuclear fusion. The finest example of this in our sky is of course the Orion Nebula, where we can see a whole cluster of stars that's being born right now. The hundreds of young stars are so hot that their radiation causes the gas cloud to ionise and make it emit light as well. Eventually, the gas cloud will be spent. It will cool down and dissipate into space whereas the cluster of young stars will slowly fall apart under the gravitational force of our galaxy and the individual stars will go their own way. The famous Double Cluster in Perseus is a fine example of a group of young stars that has just emerged from a nebula which is now gone. There may still be gas and dust filaments of the Double Cluster's parent cloud flying around, but they're no longer visible to the visual observer and would need long-exposure photographs to reveal. 

But let's fast forward many millions of years. On my sketch you see a lovely little star cluster, scientifically denominated IC1985, which lies some 1.400 lightyears distant. This cluster's a lot older than the Double Cluster or the Pleiades and most of it's stars have already reached adulthood. Strangely enough, in this case we can still see some of the original nebulosity from which the stars were born a billion years ago. I'm speculating now but perhaps the cloud wasn't dense enough to form more stars, yet it was too important to dissipate into space. Indeed, the cluster doesn't appear very rich, does it? So I assume that star formation broke off in an early phase. The nebula has cooled down now, as have the stars in the cluster, and it doesn't emit light anymore. It only reflects the light from the stars within it, or rather, from the stars that're now flying away from it. Yes, this cluster's falling apart and every single one of these stars will become like our own Sun. Planets will already have formed around them and perhaps we could already find the first traces of life there?

There's one oddball on the sketch though, and that's the very bright star somewhat further away. This star's named Atik (or omicron Persei) and it's easily visible to the naked eye, even in light-polluted skies. This star's a blue giant with a mass twenty times our Sun's and it's 80.000 times as bright. Actually it's a complex system of two massive stars that are very close and are evolving around each other so rapidly that both stars have become ellipsoids, rather than spheres. It appears that also this strange couple of giant stars originated from the same cloud as the others, but that it's taking off with greater speed than the rest. Being so large, they will consume their hydrogen much faster and therefore have much shorter lives. Analysis suggests that one of the two has already run out of hydrogen and will soon evolve into a helium-fusing red giant, becoming even hundreds of times bigger.

In the future, the stars of this cluster will lead solitary lives, apart from those that are gravitationally bound such as Atik, but also quite a few other stars as you can see here. They will become double or even multiple stars, which are very common in the universe. Perhaps there are even more double or multiple stars out there than single ones. Also Alpha Centauri, the closest star to our Solar System, is in fact a triple star which... originated from the same cradle as the Sun. Our gas cloud's now long gone, but it's a nice thought that there are still many sister stars of our Sun flying around out there. 


Friday, 13 January 2017

Razor sharp

How would our good old Milky Way look if we could see it edge on? Well, pretty much like the galaxy on this sketch. Its scientific denominator's NGC891 and you'll find it a real spectacle, even with modest telescopes. Just look at that impressive dust lane that runs around it like an equator and which seems to cut it in two from our point of view. High resolution images with the Hubble telescope revealed millions of filamentary patterns in these clouds of dust, away from the galactic centre. Scientists theorise that these patterns were caused by several supernova explosions, which blew all the dust and dark matter away.

Apart from its size and luminosity, this galaxy has much more in common with ours. Infrared images and a study of the dynamics of hydrogen in NGC891 have suggested the presence of a small central bar, just like our Milky Way. Imagine that somewhere inside that carbon copy of our galaxy, about halfway between the nucleus and the edge, lies in insignificant little star, around which orbits an even much more insignificant blue planet...

NGC891 is a part of a modest group that contains 7 regular and just as many dwarf galaxies, almost 30 million lightyears away from us.


Wednesday, 11 January 2017

Venus in colour

I've never taken a very good look at Venus. Yes, it's the brightest "star" in the sky and perhaps also the most beautiful one. But as soon as you point a telescope at it, you'll be bitterly disappointed. The reason for that is that Venus is covered with a thick layer of clouds, making it impossible to see any detail on its surface. So the only thing you'll see is a white little disk. Well, that's not entirely true because being closer to the Sun than Earth, Venus displays phases, just like our Moon. So if Venus doesn't appear as a disk, you'll see half a disk or a crescent. 

That's what I thought until now.

But my English astronomy friend Paul proved me wrong. Paul's one of the best planetary observers I know and he granted me the privilege to publish one of his sketches here on my blog. On the sketch you see four impressions of Venus. The left one's the normal telescope view and note that these observations were all made during daylight! Paul saw some clear structures in the supposedly monotonous cloud cover, especially that dark patch on the northern hemisphere. 

Next, Paul used three different colour filters. These block all the light apart from a specific colour and sometimes they make it easier to discern specific details on planets. The first is a yellow-green filter (W11) and apparently this made the south polar cap sligthly easier to see. Of course, being the hottest planet of our solar system there's absolutely no ice on Venus, but its polar atmosphere contains swirling vortices of clouds and that's precisely what Paul noted here. The deep red filter (W25A), on the other hand, seemed to kill most of the details on the planet. Finally the blue-violet filter (W47) brought out the dark markings a bit more.

So not only does this sketch demonstrate that Venus deserves a lot more attention from us astronomers, but it also gives you a very good idea of what you can expect when using colour filters.

Wednesday, 4 January 2017

Galactic tango

The tango's the dance of lovers. It's a subtle game between two passionate souls who spin and turn by their mutual forces of attraction, without yielding, until they finally succumb and the two become one. 

Now look at the two souls on my sketch. They're two reasonably small galaxies, some 26 million lightyears away from us. On the left lies NGC672, our gentleman who's leading the dance, slightly larger than his female partner on the right (IC1727). Both are very active and passionate galaxies with a large and bright central bar. NGC672 shows very delicate spiral arms, the upper one of which points to the lady on the right. 

IC1727's leaning backwards, in a classical quebrada movement. She's still resisting, but the attraction of NGC672's too strong. Her spiral arms have become twisted, irregular, the ends bending towards her lover. They're ready for the final encounter but it won't be a happy end. They'll have one last spin and then the bond will be broken. The centrifugal force of the scissors movement will break the magical embrace of dark matter that's connecting the two. IC1727 will do a pasada and then swirl away behind NGC672. Unfortunately, the two won't become one as is the case with the Flying Ghost Galaxy. But the tidal forces of the close encounter will mix up the matter in both galaxies so much that they'll be bursting with new stars. 

A one-night stand... but a lot of new life...

Isn't astronomy romantic? :-)