28:08
so uh we've been working our way through the messier catalogue making videos about every single messier object and it turns out there aren't very many pretty ones there are lots of rather boring looking clusters of stars and things but once in a while you hit a really beautiful galaxy and this is one of those it's messier 63 otherwise known as the sunflower galaxy it is a glorious looking thing i mean it's a spiral galaxy it's about 40 50 million light years away it's actually part of a group with various other galaxies of which actually another of messier's more famous and beautiful galaxies messier 51 the whirlpool galaxy is a member of the same group messier 51 is a beautiful
grand design so it has sort of two big spiral arms whereas this is what's known as a flocculant spiral in the apparently it doesn't have ground design structure we'll come back to it in a bit it has these kind of little bits of spiral arms which i guess is why it ends up being called the sunflower galaxy because they look like the little petals of a sunflower so this is a good opportunity to talk a little bit about the nature of spiral structure the classic picture people have of spiral structure is you've got a galaxy and it's got these beautiful spiral arms coming out of it and that's what galaxies like the whirlpool galaxy and various other grand design spirals look like famously there's a problem with understanding
how this structure is there or at least how it stays there in that if you look at how fast the galaxy's rotating what you find is the bits on the outside are going around at almost exactly the same speed as the bits at the inside and the reason why that is a bit weird is because if you think about it's as if you had all the stars running long distance race where they all stay in lane and if you really ran a long distance race that way the people in the outside lanes would be hugely disadvantaged because they've got a whole lot further to go the stars the material near the middle would have gone around dozens of times and this lot in the outside lanes would still be panting their way around the first lap and so it
would very rapidly get wound up as the stars on the inside went round and the stars on the outside hadn't yet completed one circuit it's a thing called the winding paradox and we sort of understand it because we don't think that the spiral arms in these grand design spirals are really kind of physical entities they're more like waves that are working their way around so just like in a water wave the individual molecules of water don't follow the wave they stay more or less where they are same here that the wave will propagate through the galaxy but the stars are just traveling along at their own particular speed as they orbit around so that's grand design spiral structure here we have the other extreme which is this
stuff called flocculant spiral structure you know you can't pick out two arms here there's just lots of little tiny bits of spiral structure and here we think there might be a different piece of physics as to what's going on so in this case we've got the center of our galaxy and what we think probably happens in systems like this is some stars start to form at some point and what happens is the very massive stars will very quickly go supernova and they'll compress gas around them and so you'll end up with other stars forming another little clusters of stars forming and so you end up with these little sort of collections of star formation occurring and of course all this stuff is orbiting around the galaxy but again
remember the stuff at the inside is going at the same speed as the stuff at the outside which essentially means the stuff further out gets left behind and so what will happen is although they might have originally formed in a circular blob if we look at them a bit later on the one on the inside will have gone further and then the stuff a bit further out wouldn't have got quite so far and so you end up forming these little bits of a spiral arm so we think probably in cases like this a lot of what we're seeing is little bits of star formation happening and then getting stretched out by this mechanism into these little sections of spiral arm which sort of form the petals of our sunflower now which is further
complicated by the fact that the other thing you can see in this picture is there are lots of dark bits and the dark bits are where there's dust lanes so as well as the stars getting stretched out there's also dust lanes that can be getting stretched out as well and are obscuring stars and just complicating the picture so what's happening is that there's light being emitted in the optical in the ultraviolet by the stars and it's being absorbed by the dust but that really just makes the dust warm up a bit like the energy doesn't disappear what happens is that light gets absorbed that energy gets absorbed by the dust then warms up a bit and then re-radiates it in the far infrared so although in this in the optical
picture here we see the dust as kind of absorbing stuff if we were to take a mid to far infrared image of this galaxy we'd see that dust glowing so here's a picture of the same galaxy as seen in the mid to far infrared so what we're seeing here is actually this dust glowing as it's warmed up to this relatively cool temperatures tens to hundreds of kelvin so low temperatures but still warm enough for it to be radiating and so we can actually see these dust lanes which were previously obscuring things actually radiating their infrared energy away and the other intriguing thing is when we looked in the optical picture there really wasn't any real evidence of any ground design but here we start seeing much longer
features so it looks like there's something else going on in this galaxy beside those little bits of style formation getting stretched out that does appear to be more kind of something closer to grand design structure in the optical part of the spectrum you have struggled to see the stars because they're being obscured by the dust in the far infrared the light that you see is dominated by the dust itself in between in the near infrared you can see the light from the stars still and actually in the near infrared the dust is pretty bad at obscuring that starlight so actually the starlight gets through the dust so we can actually see the stars in a fairly unobscured fashion by looking in the near infrared
so somewhere i have a near-infrared picture of this galaxy yeah here we go so the title of this is uncovering spiral structure and flocculant galaxies messier 63 is a classic example of a flockland galaxy and sure enough it's one of the ones that made it into their sample and they looked in the near infrared and here's their picture of it so this is a negative image which means that the dark bits you can see is actually where the stars are and if you look at this closely you can actually see that actually the flocculant structure has largely disappeared and really what you see in these slightly older but unobscured stars is just two spiral arms they're quite faint but they're definitely there so underlying
all the stuff about what's going on in the recent star formation and creating this flocculant spiral structure partly obscured by the dust it looks like the other story of spiral structure the grand design thing is also going on in this galaxy there is a wave of these slightly older stars which we can see when we look in the near infrared and we end up seeing this grand design spiral structure as well right this is a really beautiful galaxy have you waited so long to show us because we were really good and actually i was really stressed so several of us were making these videos and i was pretty strict saying look we've got to do lots of the boring objects because the trouble is the messier catalog has
got lots of boring objects in it as well as a few of these real gems well it turns out no sorry i shouldn't call them boring objects they're all interesting but they're not all necessarily pretty and so there are a few of these pretty objects and lots of objects which don't look so inspiring so we've been pretty good in that for every you know pretty object we do two or three that don't look very pretty it turns out we've slightly overdone it so we've actually got quite a few of the really nice ones left to do at this point where the s is us right which means that in any direction you look you'll see more stars say this way than you do in if you're looking this way and so actually any direction you look in the
plane of that slab which is kind of this ring around the sky you will see the milky way which is exactly what we see when you see the milky way as kind of a band across the sky
