M88 - The Leading Edge - Deep Sky Videos

All right, Professor, what have we got today from the Messier catalogue? Messier 88. That's a pretty one. It is gorgeous spiral galaxy, yeah. Have we missed that one until now? That's great. No, but it's good to save a few of the good ones up, isn't it, really? This is one of the ones that Messier himself found. In fact, he had one really good night in March 1781, I think it was, where he found nine objects in one night, of which this is one. Of course, it didn't look like that to him. He would have seen it as a bit of a fuzzy blur. If you look a bit more closely at it, there's something a bit peculiar going on, right, because it's not actually symmetric. You can see it's diffuse and fluffy on this side, but actually quite concentrated on that side. So it doesn't have a perfect symmetry to it. And there is a good reason for this. And actually, it's the same reason why Messier got lucky and found all those objects in one night, which is that this is in the Virgo cluster. So the whole load of galaxies in the same bit of the sky. And this is a spiral galaxy which is in the process of falling into the Virgo cluster. And in fact, the reason why it's sort of so squashed on this side is because it's sort of heading in that direction. So that's the side that's feeling the impact of the wind that's kind of crashing into it. So here's a paper where they were looking at NGC 4501, which is another name for Messier 88, and looking for this sort of the effect of the material getting stripped out. And sure enough, when you look at the atomic gas here, so this is the hydrogen gas in this thing, you can see there's this high density region on that leading edge and then sort of lower density material on that side. So then you can move on and look at the molecular gas as well. So there's yet another paper and NGC 4501 is one of them. And again, when you look at the molecular gas, not quite so clear in this picture, it's quite truncated on this side where it's all getting squashed up and it's more kind of diffuse on that side. Boring you with all the data here, but the last thing you can look at is what fraction of the gas is molecular versus atomic, right? How much of it is atomic hydrogen? How much of it is molecular hydrogen? So this is the ratio of the two. And what you again find is on this leading edge, there is more molecular hydrogen and less atomic hydrogen. And that's basically, again, this effect of compression that as you squash the material together, obviously it all gets kind of closer together, so you end up with more gas there. But as you squeeze atomic gas together, you start turning it into molecules, start producing molecular hydrogen as well. So the reason why astronomers are very interested in molecular hydrogen is that that's usually the density of material that turns into stars. If you just let molecular gas form naturally, then you end up making lots of stars. If you really force the molecular gas to form by compressing it very hard, you form no stars. In this case, it's sort of the star formation rate measured in that area is down by about a factor of two. So it's clear that it's getting sort of squashed a bit, which is suppressing the star formation a bit, but it's not so violent a phenomenon that it stops stars forming altogether. So most of the hydrogen out there is atomic. It's not H2, it's just H. Yeah, mostly atomic hydrogen, just because most of the gas in the universe is so diffuse that hydrogen atoms just don't bump into each other very often. So you end up not producing molecular hydrogen. Because here on Earth, you would almost never find atomic hydrogen, would you? Yeah, and it really is because most of space is very close to a vacuum, and so the densities that we're typically looking at there are very much lower than what you'd find in the lab. So this leading edge where all this compression is happening, when you first started talking about it, I was imagining it was going to be a really bright, energetic place, but because there's not much star formation there, is this actually a darker part of the galaxy? You've produced this molecular hydrogen, so you are actually making stars there. So if you look in ionised hydrogen, for example, hydrogen alpha, which is the gas that you see where there are very bright young stars that are ionising the gas, there is some there. So there is star formation going on on that leading edge, but not maybe quite as much as you would expect from the amount of molecular material there, just because this process of squashing that gas together has sort of suppressed the star formation. I mean, you'd be hard-pressed to say, you know, it looks a bit brighter, right? And I think that basically is reflecting this star formation that's going on there. But there's two things going on there, right? Because partly it's brighter just because it's got squashed, and so the stars are closer together, so you end up with a kind of a higher brightness area. But also there is a degree of star formation going on there as well. What would it be like to live near that leading edge on a planet around a star there compared to other neighbourhoods of the galaxy? I doubt you'd notice, to be honest. It is one of those weird things about galaxies. They're mostly empty space, you know, in terms of if you were actually so close to it that you were living on one of the stars within that galaxy, you know, the next nearest star would still be light years away. So you probably wouldn't notice very much different there compared to any other part of the galaxy. Does M88 have a cool name? It looks good enough that it feels like it should have a cool name. It should do, doesn't it? Not that I'm aware of, no. You guys have got to catch up with naming these galaxies. There's just too many things out there, that's the trouble. Too many cool things to look at, you can't give them all names. And perhaps something we call the destruction timescale, which is quite a doomsday thing to talk about. So once they have formed, there's a couple of things that can happen. You get star-star interactions in a globular cluster, so you have like flybys of stars.