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i have a spiral galaxy and i'm very happy about the fact that i have a spiral galaxy it's messier 100. this is ngc 4321 and it's what's called a grand design spiral galaxy in the constellation of coma berenices which i think is pronounced properly grand design really means that it's very well structured like you can see the very specific structure of the spiral arms rather than some spirals that can kind of look fluffy we call them flocculant which literally means fluffy as well which is quite nice i think it was sort of like a flock of sheep kind of thing stop talking about sheep and talk about galaxies so this is about 60 of the size of the milky way it's in the very famous cluster of galaxies called
the virgo cluster which is strange for a spiral because you don't tend to find these beautiful spiral galaxies in clusters because clusters of galaxies you get lots of interactions between galaxies and they can basically gravitationally ruin this beautiful spiral structure in the beautiful shape of these but this one has managed to keep hold of its spiral structure which is quite nice messier actually described this as being very difficult to characterize and couldn't actually tell that it was well what he called at the time a spiral nebula obviously we know now that it's a spiral galaxy it's not just a spiral galaxy there is a bar very much in the center you just can't see it on this image because it's so
oversaturated but if you look at the hubble space telescope image you can just about see this bar-like structure in the very center people thought it was surrounded by a ring but now you can actually see that it's two very small spiral arms that it's surrounded by so it's very much in the center this is something like the inner killer parser in the galaxy which is something like three percent of the galaxy's overall size it means that it's actually triggering a lot of star formation because it's i mean it's so bright you can tell there's a lot going on in that region first of all but also the presence of the bar and the presence of those spiral arms will essentially be moving a lot of gas around that galaxy
as well and where it gets compressed is where you're gonna form a lot of stars which is why you can also see in this image just down here that is a supernova which is why it's so bright in comparison to the rest of the galaxy yeah you can pick out some individual stars but that one is incredibly bright and in fact we've actually recorded five supernova from messier 100 which is a lot for a single galaxy it's probably quite so high because it's had what we call a star burst so this is where it's had a huge burst of star formation at some point in its history where a lot of stars have all formed at once presumably triggered by some form of interaction with another galaxy or maybe because of the bar in
the center or the spiral arms and now all of the massive stars that formed in that burst are dying off and so we're seeing a lot more supernova than we would expect to see the thing is for the shape of the galaxy that this is this beautiful spiral shape we'd actually expect the whole galaxy to be as bright as that central region where we think there's that starburst that's taking place the fact that it's not is really interesting for spiral galaxies we expect them to be very blue and very star forming blue light essentially means the hottest brightest biggest stars in galaxies where you've got a fresh gas supply all the time to make new stars so fresh hydrogen gas you're
going to form new stars all the time and you're going to be following the big stars and so you'll have a very blue galaxy in a galaxy that's sort of not got any more gas for stars or it's had its supply cut off you end up with a galaxy that's sort of reddish in color there's clearly not very many stars forming and we tend to call it like a dead galaxy but what we tend to see for those galaxies is that they aren't spiral shaped they are these huge big elliptical blob shapes kind of like messier 87 that we've done on this channel before and we think that those two things can correlate the fact that they can stop forming stars and they can change their shape at the same time
and we think it happens in clusters because you can have interactions and mergers first of all the mergers and the interactions ruin the shape but also they can heat or expel the gas needed for star formation so the fact that this spiral galaxy this messier 100 is in a cluster is probably why it's got this reduced star formation rate and it probably will end up dying as a spiral rather than dying as an elliptical perhaps in the end as well the way that we think a lot of spiral galaxies do go through this process of cutting off their star formation rate it's a process we call quenching but the process by which this happens in clusters tends to be thought of something called ram
pressure stripping and people might have heard of this because it's responsible for the jellyfish galaxies and the jellyfish galaxies essentially end up looking like jellyfish because as this galaxy if you imagine it falling into a very hot dense cluster it can get all of its gas stripped off in this huge big long tail behind it and also you can then trigger more star formation in that tail and it literally ends up looking like a jellyfish this one though doesn't look like a jellyfish it's very clearly still a happy spiral galaxy that's managed to keep its shape so we have to ask ourselves well how has it been quenched in this cluster of galaxies if it's not gone through the typical
round pressure stripping that we'd expect i have to admit this is actually what i research so i'm very excited about getting to talk about this on deep sky videos and i just wanted to show you um when i give talks to other physics departments and other astronomy departments uh across the uk across the world i give a talk that explains the different ways that spiral galaxies can be quenched in a cluster i try and do it in a bit of a different way i represent each of these processes with emojis because why not people actually go away from the talk actually remembering the emojis and remembering these different processes that can happen so it's all to do with how what we call the interstellar medium in a galaxy so this is the gas and dust in
between the stars in a galaxy the interstellar medium and the intracluster medium so that is the gas in between the galaxies inside the cluster so it's all to do with the interaction between those two things because if you have a huge cluster of galaxies then the gas between those galaxies is literally heated up by the movement of those things just like stars in a star cluster it's like an open cluster or a globular cluster that we talk about in this channel how they move much more quickly depending on how many stars that are in the cluster you know you literally increase the gravitational energy in there by increasing the number of galaxies in a galaxy cluster you do the same thing the galaxies move much quicker and the gas in between them gets
heated by the fact that there's a lot more energy in that system so you end up with galaxies that have lots of cold gas ready to make brand new stars in falling on a cluster that's incredibly hot where the gas is moving and the molecules are moving very quickly and so the interaction between those two things can cause either the gas and the galaxies to be heated in which case it can't be used for star formation or expelled in some way so one of the ways you can do that is through what's called thermal evaporation which is the interaction of the interstellar medium with the intergalactic medium to heat it up another way you can do that is through harassment so that would be repeated high-speed interactions between two galaxies which again would cause the
gas in the galaxies to get heated because you add more energy to the system another one is called viscous stripping which is again a really weird one to consider but it's essentially if you have an interaction between two galaxies you can actually disrupt the shape or the disc in a galaxy so that sort of flat spiral shape and you can cause what we call an instability so you can essentially like rock the orbits a little bit not just of the stars but also the gas and then you can actually cause a big outflow out of the galaxy so it can essentially just throw out a load of its gas because you've interrupted the orbit so much and the last one we talk about is called starvation which is all to do with the
surrounding galaxies what we call halo so you might have heard of a dark matter halo that surrounds the entire galaxy but because that mass is there it also attracts a lot of gas to stay there as well that can sort of be used as the supply into the galaxy because it will be very cold because it's outside of the galaxy away from all those internal effects and so what we think happens in starvation is that halo interacts with the surrounding intergalactic medium in a cluster and can actually completely strip away that halo so you remove the galaxy's supply basically and so all of those things you know family evaporation risk of stripping harassment starvation they're very violent there's sort of
this like push to rename all of these processes like possibly some things that are not as violent um but i guess the violent sort of words actually reflect how impactful they are on a galaxy and how much of an effect that they can have and so with messier 100 we have to debate whether okay none of those processes that i mentioned i didn't say any of them could change the shape most of the stuff that's happening is that you're heating or stripping the gas supply in some way and so you're never going to see that in the stars that you observe and the only way that we can tell is if we go away and actually look at the gas either with radio observations or with infrared observations as well sometimes
that can tell us more about what's happened in the history but it's very difficult to see when we first look at it in the stars all we end up seeing is that dimming from the bright blue that we'd expect this sort of reddish color with all of these supernovas showing us that it's probably post star burst but also in the process of being environmentally quenched as well if it was left alone to its own nature it wouldn't be this way and it's sort of this fight between like nature versus nurture they talk about in biology this idea of whether this process of quenching is happening from the inside outwards in which case it would probably be down to the galaxy's internal nature or whether it's happening from outside
inwards because of the nurture of the galaxy's environment and i think in messier 100's case it's probably a little bit of both because yes it's being environmentally quenched by the fact that you're clearly quenching the disk that surrounding area that's not as bright and that's what's happening first and it's happening from the outside in because of the environment but also that little bar in the center with those little rings of spiral arms outside of it that i said was probably funneling gas into the center where it's making a lot more stars in a big starburst if you make a lot of stars at once in a big starburst you use up a lot of your gas for stars very quickly and so you haven't really got any left over for subsequent
generations of stars and so by having this big period of star formation in the center it's effectively like shooting itself in the foot of the galaxy right it's going to quench itself from the inside out as well as the outside in like six years old and wanted a telescope for christmas kind of thing like i was always into space like space books on the shelf getting little telescopes always wanting to go out and see the sky i want to steal the crown i wonder where it is oh i know they go on wikipedia where is the crown kept oh some place called the tower of london apparently but that's like saying well let's not put the gold in fort knox because that's when they'll expect us to have put the gold it's like yeah that's what we built
that's where we put the gold i tell you what would be safer than fort knox though a place you haven't heard of that they don't announce and don't say where it is that's true yeah rather than for instance the crown would be a lot they could find safer places for the crown than on the head of a senior citizen
