Wednesday, 6 April 2016

More beauty in Leo

In one of my previous posts I talked about tree lovely galaxies that the lioness bares in her belly. But if we move slightly towards her chest (wow... soon I can start writing romance novels... :-) ) we find more beauties. On this sketch you can see the M96 group of galaxies. In reality this group is still much larger than what I could catch with the already enormous field of view of my binoculars and it contains at least 24 members, 4 of which are visible here. 

M96 is the brightest of them all and proudly rests at the centre of my sketch. It's a spiral galaxy with rather weak but still clearly visible spiral arms, about the same size as our own galaxy. Measurements revealed that its gravitational centre is not in the middle but a bit off due to gravitational interaction with the other members in the group. Interesting to note is that ultraviolet emissions from the core suggest that it contains a supermassive black hole!

M95 can be found on the right. It's a galaxy with a fairly strange shape because its spiral arms appear to form a ring around the centre, rather than to originate from it. In reality it's a "bar-type" galaxy, which means that it has a bar-shaped structure across its centre from which originate the spiral arms, but its bar is rather weak and hardly visible. It certainly wasn't visible through my binos although I could see a hint of the ring of spiral arms. The nucleus itself is surrounded by an enormous star-forming region some 2.000 lightyears across. 

Then we move to the little group on the top-left. The brightest member of this subgroup is denominated M105. It's an "elliptical" galaxy, meaning that it lacks the spiral arms and structure of spiral or lenticular galaxies. Once it was believed that these smooth and shapeless galaxies were young and that they'd evolve into spiral galaxies, but this turned out to be false. On the contrary, star formation is very low in them and most stars are much older than the stars found in spiral galaxies.  However, it contains an even bigger black hole that the one in M96: it has a mass of 2*108 solar masses!
To the left of M105 we find its closest companion, denominated NGC3384. It's a lenticular or disk-shaped galaxy. These are somewhat intermediate between elliptical and spiral galaxies and together with the former they tend to be quite old with little star formation going on, although they do have a much clearer structure. Over 80% of the stars in this galaxy were found to be more than a billion years old. Invisible to amateur telescopes but still very interesting is that NGC3384 and M105 share a large ring of neutral hydrogen, 650.000 lightyears in size, in which star formation has been observed. 

Last but not least, I present you a challenge. There's a small, third galaxy near the M105 subgroup and I hope that you can find it. It was extremely difficult to see through my binos anyway so I wanted to let you suffer just as much as I did when I was trying to locate it. :-) It's referred to as NGC3389 and although it appears to be a member of this subgroup and hence as a member of the M96 galaxy cluster, it isn't part of it at all! It lies twice as far away from us and is therefore a remote background object that only coincidentally seems to reside close to M105 and NGC3384. It's also a completely different type of galaxy than the other two, with a clear spiral structure and a high emission of blue light which indicates a huge quantity of active hydrogen and a lot of very young stars. But unfortunately this little galaxy ended up in a remote and isolated part of our universe, without any close companion.  

The M96 cluster lies at a distance of 32 million lightyears and is in turn part of the Virgo supercluster of galaxies. This supercluster is truly gigantic as it not only contains the already vast and crowded Virgo cluster, but also the M101 group, the M82 group, the M65 group, the M51 group, the Draco group and... our own local group of galaxies. The supercluster's a whopping 110 million lightyears across and is defined as such because there is gravitational interaction between its various members, however distant. And here's the good news: there are millions of these superclusters in our universe. How about that for perspective?

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