Caoimhín's Content

Today, we are going to take a look at a couple of galaxies and particularly at the different types of galaxy. We’re going to push a little bit past midnight, we don’t have to wait too long for one of the richest areas of the sky in terms of galaxies to become visible. This is a pretty good time of year to look for galaxies because the glow of the Milky Way isn’t going to be in the way.

During wintertime the galaxy’s core, the core of the Milky Way, is pretty much behind the Sun, so of course that means we don’t get to see as much of the Milky Way. However, to look for other galaxies we need to look outside of the Milky Way, so it being out of the way is beneficial. Looking over to the southeast at about 12:30, this area of the sky is quite rich in galaxies. At just half past midnight, Jupiter has just passed high in the south. It’s after passing its opposition, Jupiter is still very close to opposition, it’s still a great time to look for it, it will still be close to due south at local midnight. If you take a look over towards the southeast at just about half past midnight, you should spot the constellation of Leo. Looking at it from a city, the trapezoidal sort of body of Leo is pretty obvious, but the sickle at the top is not so clear. We’re going to get rid of a little bit of the light pollution just so we can see a little bit more. Going to a Bortle class 3 or so, this isn’t a perfectly dark sky, but it would be considered a rural sky, and that gives us a better idea of the shape of Leo. Following the zodiac down into the east, after Leo is Virgo, which is sort of a mess of stars. Its shape isn’t very obvious, and most Virgo is down below Arcturus, like the bright star Spica. We’re taking a look just after the tail of Leo and kind of ahead of the beginning of Virgo.

This area of the sky is rich in galaxies and many of them are reasonably easy to see as kind of fuzzy shapes that aren’t quite stars, many of them would be visible as fuzzy shapes even through binoculars. To get a good view of them as galaxies, of course, we need to take an even closer look with a telescope. There are many galaxies in this region of the sky and there are many different kinds of galaxies. Stellarium makes it even bit easier, with markers for deep sky objects. This will give you an even better idea of how many galaxies are in this area, there’s some globular clusters visible there as well. Zooming in to take a closer look, first off at a M49. M49 is an elliptical galaxy, and if we take a look at its description, it’s E2. The E tells us that this is an elliptical galaxy, and the 2 that it is a little bit squished. It’s not completely spherical or close to spherical, like an E0, it’s a little bit more elliptical, it’s a little bit more squished. However, it’s still not flat enough to be a lenticular galaxy or a spiral galaxy. With galaxies, they’re often classified according to their shape, and it gives us the little number-letter codes that we will use here. If we look around to a few other galaxies, you’ll see some different types.

Looking at the code for the Lost Galaxy of Copeland, it’s SAB. The S stands for spiral, a spiral AB galaxy. The AB indicates that it’s not really barred, it’s more of a normal spiral galaxy, but it is a little bit of a mix. It’s AB, not just A or B. The nearby Lost Galaxy is SB0 and although it’s tough to see, the letter code tells us that it is a spiral barred galaxy. One of the first systems to divide up galaxies into different types was the Hubble system of classification, and it really divided galaxies into three types. The elliptical, almost round galaxies, the spiral galaxies, and the spiral barred galaxies. There are further distinctions, which add more letters and numbers. The Swelling Spiral Galaxy, M61, is a galaxy that may become a ring shaped galaxy in the future, with a code of SAB(rs)bc. The “rs” here is an indicator that it may end up having a ring of material around its center, and its spiral arms don’t start directly from the center, they extend out a little bit. This is common. Barred spiral galaxies seem to be a little more common than normal, I say normal, spiral galaxies. Unbarred spiral galaxies are the exception, barred spiral galaxies seem to be more common.

NGC 4393 is a barred spiral galaxy, with a code of SB(r)b. It has a quite clear bar in the middle, but its arms almost form two separate rings. This ring shape is what gives the “r” that we’re seeing in the code, and the B shows that it is a spiral barred galaxy. It’s also being shown as an active galaxy. Active galaxies are usually galaxies where the black hole in the center is sucking in material, and that produces jets of material coming away from the galaxy. It’s got an active nucleus, and an active galactic nucleus is really just a black hole that’s generating jets because it’s sucking in material. Moving onto M85, this is a normal spiral galaxy, with code SA. I keep saying normal, but really the barred spiral galaxies are the norm, about 2/3 of spiral galaxies are barred spiral galaxies, only about a third are not. Looking at the Blowdryer Galaxy, it does mostly look like a spiral, there’s not much evidence of barring here. However, it does have the SAB(s) with an “s”, not an “rs” because it’s definitely still a spiral, it’s not showing much of a ring shaped structure. This division of galaxies into elliptical galaxies, spiral galaxies and spiral barred galaxies, produces a sort of a three way diagram. The Silver Streak Galaxy, only has a two, rather than any letters, but this galaxy is tilted quite extremely, so we’re not getting to see much of whether or not it’s a barred or spiral. We’re not really getting to see it face on, which is what we need to do in order to easily classify it. By looking at the behavior of a galaxy, you can sometimes figure out what shape it is even if you can’t see it fully.

The three divisions into spiral, spiral, barred and elliptical, produces a sort of a shape like a Y. In the center of the Y are lenticular galaxies. So we’re going to have a look for a lenticular galaxy. IC 1101 is one such galaxy, with a code of E/S0, which means it’s elliptical/lenticular. There isn’t a picture for every galaxy in Stellarium, and it looks like that’s a galaxy that doesn’t have a picture. Thankfully we can still get an idea of roughly what shape it should be thanks to those letters and numbers. Another example of a lenticular galaxy is the Spindle Galaxy, it is a flat galaxy that isn’t a spiral. A spiral galaxy has spiral arms, an elliptical galaxy is round, but a flat galaxy that doesn’t have arms, that’s a lenticular galaxy. Lenticular is shaped like a lens, and as I mentioned for very fast spinning stars in a previous piece, they’re often lens shaped as well. Looking to the Tiger’s Eye Galaxy, another spiral armed galaxy, even though the spirals are very tight here, and even though we are looking at the galaxy at a little bit of an angle, it’s not exactly dead on, we can still see that it doesn’t have that strong bar across the center there. The Milky Way is a barred spiral galaxy, we have that bar in the center and that is the most common kind of spiral galaxy.

The tuning fork diagram, the Y shape I mentioned above, does lay out the shapes of the galaxies quite well. On one end of the diagram you’ve got very elliptical elliptical galaxies, like M89 and M85, that are practically balls of stars. As you move along the tuning fork, the ellipses get flatter and flatter until you come to lenticular galaxies. One of the galaxies In Markarian’s chain, M86, is a lenticular galaxy. It’s kind of hard to tell that it’s not just a ball of stars here, but it is a little bit more squished than a true elliptical galaxy. The split in the tuning fork, the split in this Y shape, is after this flat lenticular shape. Once the galaxy has arms, it’s either going to be a barred spiral or an unbarred spiral. The tuning fork diagram, purely talks about the shape of the galaxies, but the shape of the galaxies doesn’t have much to do with their evolution, or at least it isn’t, there isn’t a direct relationship in the evolution. So, for example, the spiral galaxies and the spiral barred galaxies, they don’t necessarily become more or less barred, more or less spiral over time, and elliptical galaxies don’t necessarily become more elliptical or more lenticular over time either.

Rather, what happens is that these galaxies, spiral galaxies and barred spiral galaxies, are smaller and they often collide to form elliptical galaxies. Elliptical galaxies of various degrees of eccentricity, they form from collisions of smaller galaxies. Now, of course, these things take a very long time to occur. We know, or at least we can estimate, that spiral galaxies come together to form elliptical galaxies because elliptical galaxies are almost always larger, and because we’ve seen spiral galaxies colliding, or at least we’ve caught spiral galaxies in mid collision. Moving into Leo, there are the Leo Triplets, two spiral armed galaxies and another galaxy that’s really edge on so it’s tough to see exactly how much of a spiral it has. We’re moving up into Leo here, away from Virgo, to see some of the other galaxies. This area of the sky, it’s a rich area of the sky and stretches across a broad area of the sky. Continuing to NGC 3384, an S0 means we’ve got a lenticular galaxy, and one that is visibly long, lenticular, oblate in shape. Right next to it is M105, an E1, so very elliptical, a very much round ball of stars. Down below that pair is NGC 3389 which looks like a pretty irregular galaxy to me. It may be an irregular spiral with some trace of arms, but definitely not the clear obvious shape of the more obvious spiral galaxies.

We’re going to take a look for some interacting galaxies. There’s not an image provided for all of the galaxies, but there are a few with example images. The Meat Hook Galaxy or the Cobra Galaxy has a distorted shape, hence its name. This is because of it and the Mouse Galaxy, these two galaxies beginning to interact, beginning to change each other’s shape. There is another galaxy, the Antenna Galaxy, and not the Super Antenna Galaxy, which is really two interacting. This is an example of two spiral galaxies that are really mid collision. They’ve completely lost their spiral shape, but they will eventually coalesce into a more elliptical shape, or at least that’s how it seems to be. We can’t see into the future and we can’t observe these galaxies over the billions of years that it takes for them to change shape, we just haven’t been around long enough. However, based on everything we can observe, we can see these spiral galaxies and barred spiral galaxies becoming elliptical galaxies, at least that’s what they seem to do.

So I hope you get a chance to see some of these galaxies, it’s a fantastic area of the sky to look in and a great time of year at which to do it. I hope you get to see some of these galaxies and even if you don’t, at least you’ve learned a little bit about them here. If you enjoyed this piece, please do like it. If you like this kind of content, then please subscribe to this website and my YouTube channel. Thank you very much for watching and hopefully I’ll see you back here next time.