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Let's talk about Messier objects. Yes, Messier 86 and why I had to empty the fridge for this conversation. Ovva. Messier 86. You won't be surprised if I say I don't even know what it is This is an elliptical galaxy. It is located in the Virgo cluster. So, in this relatively close, rich cluster of galaxies. In fact, it's one of those galaxies that Messier himself seems to have discovered sometime in the 1780s. So this is one of his unique discoveries. The Virgo cluster contains a few really large galaxies and many small ones. This one is somewhere in the middle. You present it as rather mediocre at this stage. So, a medium- sized galaxy in a well-known old cluster of galaxies.
The most interesting thing begins when you investigate the motion within a galaxy, or even the motion of the galaxy itself. Remember that we are studying motion by taking the spectrum of a galaxy. We split light into the colors of the rainbow. Then we look for these small features related to absorption by different chemical elements. And then we use the Doppler effect: if these lines are shifted slightly to the red side, it means that the object is moving away from us. If they are shifted to the blue side, they are approaching us. And the very unusual thing about Messier 86 is that it has a blue shift. It is approaching us at a speed of about 240 km/s.
Why is this strange? Could it not be that its motion within the Virgo cluster is currently directed towards us, and in 100,000 years it will turn around and move away? This is actually the main part of the story. But remember, there's something else going on -the expansion of the Universe. Part of the reason why we see redshift in galaxies, and why the vast majority of galaxies have redshifts, is that the expansion of the Universe stretches light. So the wavelength is stretched to increasingly red values. Most galaxies have a redshift, and the further we move away, the more Hubble's law becomes apparent: if the distance is twice as great, the redshift is twice as strong. So you would think that for the Virgo cluster, which is 45 million light years away, we
should see this redshift effect, and in fact we should see a redshift from the expansion of the universe of about 1000 km/s or so. The fact that this object is actually approaching us means that it is a combination of two effects: the expansion of the Universe is causing it to move away from us at a speed of 1000 km/s, or at least appear to be moving away at that speed. But, as you pointed out, there are also movements within the cluster that more than compensate for this. So this object is moving rapidly towards us. In fact, it is flying almost directly at us at a speed of about 12,300 km/s within the cluster. And when you add these two metrics together, the overall effect is that the object is still heading towards us.
So for something to have a blue shift when it's far away, it really has to be moving towards us. Certainly. In fact, we have evidence that this object is moving at quite a high speed, because if you look at a galaxy in X-rays, you can see the galaxy itself and a plume of material behind it-this is very hot gas that emits X- rays. The reason for this is that the object is crashing into the gas contained in the Virgo Cluster. The collision of gas in a galaxy with gas in a cluster causes it to be ejected as the galaxy moves through it. What are the consequences of losing gas? You probably have significantly less star formation. Yes, I mean that this is already an
early-type galaxy, that is, an elliptical galaxy. It probably did n't have a lot of star formation going on anyway, but if a galaxy like the Milky Way were to fall into a cluster, it would almost certainly stop star formation because you're losing the raw materials to make new stars. So if you lose gas, do you become a boring dead galaxy? Not the best place for parties. Yes, you're turning into one of those boring, uniform, passive galaxies that gets redder and redder over time because you're no longer creating those wonderful, exciting, bright blue stars that make galaxies shine. And so that I understand correctly: what exactly is causing her to lose gas? The gravitational pull of all other objects?
No, it's dynamic pressure. So it really does crash into the gas that's in the cluster. And the gas in this galaxy just hits it and gets pushed out. So you can not only measure the velocity of the entire galaxy by observing the Doppler shift in the spectra, but you can also look at different areas within the galaxy and see how individual parts of it are moving. M86 is slightly flattened. So you expect to see it flattened as the object rotates, and when something rotates you expect one side to move toward you and the other to move away. You know, you also have to exclude the motion of the entire galaxy, but then you have to see the rotation of the object itself, which is causing it to flatten out. And that's why galaxies like the Milky Way are
flattened, because they're rotating disks. Okay, this object is a little flattened. So you expect to see a little bit of rotation, and you expect it to happen around the minor axis. That is, around the short axis of the object, it is compressed just like that . So you expect one part to be moving towards you and the other moving away. Yes, but it's not what you see at all. So, let me show you what you actually see in M86. So, M86, also known as NGC 4406. Here it is according to the survey data under the name Sauron. The ellipses here show how flattened the galaxy is. Since it is flattened around its short axis, we expected to see it rotating in that direction. So, you know, maybe that side
should be shifted to the red region of the spectrum, and that side should be shifted to the blue region. This is not at all what you see. In the center you see a tiny bit of rotation. It's one of those things called a kinematically separated core, where the middle takes on a life of its own. I think Megan made a video about one of these a while ago, but basically it means there's something weird going on right in the center. This is probably a place where something fell, merged with it and now continues to live its own life. But at larger radii, instead of rotating around this axis, the short axis, you can actually see that here the blue color is on top and the red color is on the bottom. This means that it rotates around its long axis,
not its short axis. It's kind of like an elongated object that rotates around its long axis, which is very, very strange. Almost like a cigar or something rolling down a hill. That's right. Yes. Like, like spinning around a cigar. And this is very strange for many reasons, partly because it doesn't explain why the object is oblate. If you expected the object to be flattened due to its rotation, that's clearly not the case. Um, actually, it's even stranger, because it turns out there's no way. If the object is oblate, you know, if it's essentially a kind of oblate disk, then you can say, " Okay, maybe this is a
disk, and everything is kind of rotating, you know, around. well, kind of weirdly around this disk," and you see this circulation around the surface of the disk and underneath it. But it turns out that there are no families of orbits that would provide this. If you actually calculate how things move in a galaxy, in an elliptical galaxy, objects can have what are called " box" orbits, which simply means they move wherever they want. Or they may move in "tubular" orbits that bypass the center of the galaxy and move more or less in a circle. It is the ones that move in a circle that are useful for creating the effect of rotation, because, of course, it is thanks to them that rotation occurs, and not just chaotic movement in different directions. And if
you look at these families of tubular orbits, you'll see that they only exist around the minor axis. In other words, for something oblate, like a disk, the only way to rotate is around its shortest axis. So this object cannot be in the shape of a disk. It should be what is called a triaxial ellipsoid. That's why I emptied the refrigerator. Okay. What do you have? Because I have a three-axis ellipsoid for you. This is a kiwi. And kiwis are interesting because they are triaxial ellipsoids. They don't have an axis of symmetry, right? You could say.well, you know, the obvious feature of kiwi is having a long axis and a short axis.
It is longer in one direction than in the other. But if you look at it from the end, it's still not round. In fact, one axis is shorter and the other is slightly longer. So it has three main axes, right? The long axis, the mid- axis-kind of medium-sized- and the short axis. The most interesting thing is that when you start counting orbits in triaxial ellipsoids, it turns out that there are two different families of such tubular orbits that move in a circle. There are those that move around the shortest axis. So they are indeed similar to those in a disk galaxy, but there is also a family that rotates around its longest axis. You could, if you made a kiwi out of stars, eventually make them rotate around their longest axis. So what we saw in M86 is typical of
what you would expect if the internal shape of the galaxy were like a kiwi. Professor, what made this galaxy look like a kiwi anyway? This is unclear. I mean, because of that kinematically separated core in the middle, we know this thing has had a pretty turbulent history. So, something hit her. She was pushed quite a bit. Now it is falling into a cluster. It probably encountered other galaxies along the way. So it wouldn't be a big surprise if her form was quite distorted. And so it just took on a shape that is not axisymmetric. It is no longer a disc or
cigar shape. It's something in between that has three different axes of symmetry. It is shaped like a kiwi. If only this galaxy could talk, what a story it would tell. One last thing to test, because you don't want to fly all the way to Pluto and not take a picture. So the first thing they did was, obviously, they opened up something like a lens cap, if you will. It was like a hinged door closing in on Lori.
