The Science and Beauty of Nebulae, Carolin Crawford

well welcome welcome to this last in our present series on the theme of beauty and for me one of the most memorable talks we've had this term has been Frank will checks lecture on quantum Beauty which concerned things which are about as small as you can get and now we're going to the other extreme with things that are about as large as you can get now as you know we had planned to have Carolyn Porco but at the weekend she fell on the ice and the Rocky Mountains and was quite badly bashed and bruised and so on and she's seen emailed us today to say that she's recovering well which was good and she's asked me to pass on her regrets to you we are however amazingly fortunate to have another distinguished astronomer Carolyn Crawford to speak to us about the science and beauty of nebulae dr. Crawford works at the Institute of astronomy and in emmanuel college here in Cambridge she was educated in Cambridge and her research has been on the properties of massive clusters and very large radio sources exploring them for overall wide range of wavelengths but she's actually known to a much larger audience as a leading public speaker and broadcaster on science and astronomy and in this respect if this respect only she Carolyn Crawford is to astronomy what Geoffrey Boycott is to cricket who better to tell us about the science behind cosmic beauty [Applause] so this evening stork is still going to be on the idea of cosmic Beauty and I've used it as an exercise to showcase some of the most spectacular and beautiful images from both ground-based and space-based telescope now I'm showing you these pictures because they're beautiful and you know the odd ooh and I wouldn't go amiss I hope you appreciate them but I'm showing you them because they're also scientifically very interesting and even if you recognize some of these pictures and I'm sure you will I want you to look at them with new eyes I want to teach you how to read the science that's going on in these images what you're looking at what the cosmic objects are and how they interrelate with each other and ideally get you to understand the science behind the beautiful images that we're going to be looking at so let's start so we live in a galaxy that resembles this one it's a spiral galaxy a hundred thousand million stars all held together by gravity and the galaxy is shaped like a flat disk or the analogy we sometimes use is two fried eggs stuck back-to-back and if the egg whites form a big disc and the egg yolks form a ball of stars in the middle now in our galaxy we live about halfway out from the center out to the edge and this disk is traced by brilliant spiral arms you can see this in this image that they're lined by large blue clusters of stars beautiful arcs around and we live in one spiral arm just like this so when we look into our sky at night and we see all the stars all those stars are part of our Milky Way and in addition we can see blue star clusters which live in the next spiral arm and within our own spiral arm of the galaxy so for example clusters like these those of you who might be amateur astronomers may know of the Perseus double cluster little double cluster of stars you can see in the constellation of Perseus if you got really good eyes you can see in the unaided eye certainly very clear in a small telescope or binoculars and these are bright because they're close to us we're seeing through our own spiral arm and we've seen them in X barrel arm over in the Milky Way so stars are the most obvious feature of a galaxy but they're not really what I'm going to be talking about today I'm going to be talking about the matter that lies between the stars we're told that space is a vacuum yes it's a much better vacuum probably a million times better than any vacuum we could get here on earth but it's still not completely devoid of matter so in a volume say something like this volume of this soda can there might be perhaps a dozen atoms of hydrogen if you're very lucky a single grain of dust and I'll tell you about dust later it's still not completely empty and the volumes of space are so enormous that it still stacks up to quite an appreciable about a matter between the stars probably about 10% of the mass that you see in all the stars there's about 10% of that mass in gas lying between the stars so tonight's talk is not just about the stars it's about the space between the stars and the matter that lies there some of it is left over from when the galaxies formed 11 12 billion years ago some of it has been cooked in the Centers of stars and then fuller flung out at the end of their lives and mixed in and mostly it's hydrogen and helium mostly hydrogen a little bit of helium and an even smaller amount of heavier chemical elements and this interstellar medium as we call it is of fundamental importance this is the reservoir from which stars form and it's not just the reservoir from which stars form but also any planets around those stars and any life forms on those planets as well so you all originate from this matter that lies between the stars now here's my schematic of a starry volume of space in our galaxy now not all this gas is apparent throughout the galaxy there's a very hot very sparse medium it's so hot it's giving off x-rays and tall extents and purposes for this talk we're going to ignore it it's invisible it's transparent for what we're talking about today there isn't much matter in it but it fills most of the volume of space embedded within that are colder clouds and embedded in those are even colder clouds now these diffuse clouds are denser they've probably got an equivalent amount of mass in them but because they're much more compressed they don't occupy so much volume and most of them lie in that flat disk of our galaxy and these clouds are so cold that maybe most of the atoms in them oh it's mainly neutral hydrogen atoms that any light and irradiation they give off we could only detect with radio telescopes like the ones down Barton Road so again this is largely invisible for the sake of tonight's talk however when these clouds are close to a heat source they get heated up they get heated up to temperatures of thousands of degrees and at that point if you pump that much energy into atoms they begin to glow by their own light and they glow and become visible and those are the nebulae that were mainly going to be concentrating on today so along the spiral arms you've got those bright blue stars so when we look at a galaxy you can see that the spiral arms are traced not just by the bright blue star clusters but by pink clouds of gas and if we zoom in just in the corner of this bit of this galaxy you'll see that the gas surrounds clear blue star clusters this is an external galaxy again we have many examples that I'm going to be showing you tonight that lie much closer to us in our own galaxy one such is the rosette nebula and I'm going to be coming back to that in a minute but I like just a little diversion about the images themselves and about the colors that we're using because it's often a question I get asked you will see in all the galaxies nearly all the images a lot of these nebulae that I'm showing you are pink now and just to stress I'm sure I don't need to say this it's very erudite audience but nebulae nebula is Latin for cloud so really I'm just discussing clouds in space and we call them by this name nebulae so this cloud is glowing a characteristic pink and what you'll find is that most of the clouds and images that I show you pink already pink is going to be a dominant color and that's because it's being emitted by hydrogen atoms and if you excite hydrogen atoms that they glow there and radiation they glow this pink color so let's just talk a bit about color and what it teaches us before we get on to the rest of the beautiful images astronomers have to be incredibly clever well I guess I'd say that anyway but you're gonna realize that we can explore our own solar system but anything outside our own solar system the only way we learn what's out there how it behaves is through the light it admits and so we have to learn about stuff by analyzing and interpreting that light now clearly from images we can get a distribution of the light and the matter emitting it but the colors can give us further information so again this is a very simplistic level but just to give you the idea that a star like our Sun it emits all the colors of the rainbow and I'm going to concentrate on the optical wave band so again if you're familiar with these units we're going from 400 nanometers so this is short wavelength these are blue colors up to about 700 nanometers which are red colors and the Sun emits in all colors and that's going to be true for lots of stars that you'll see they shine nearly all color summer ripped bluer than others some are a bit yellow as some are a bit redder but they get to give off optical light at all wavelengths the same is not true about some of the gas atoms in these clouds that I'm going to be talking about so inside an atom at the very core there is an atomic nucleus and that's surrounded by a cloud of electrons and if these atoms are irradiated you've got energetic ultraviolet light shines on these gas atoms they can absorb the photons and borrow the energy and the way it works is perhaps some of these electrons in the cloud may shift their position their energy levels in that cloud of electrons they more or less burrow the energy for a while and then the atom emits the photon again and emits color that's how they the atom glows the the end point what I'm trying to say here is that the color or the light that the atom radiates what is absorbed the energy played with it a bit and then gives it out again as a photon that light is very much determined by the structure within the atom so if you heat different atoms of different elements then and you give them energy then they glow different colors and they glow characteristic colors so for example if I heated a cloud of hydrogen and again we've got the scale of wavelength here from 400 to 700 nanometers of blue to red they just give off discrete photons of specific colors and because it's to do with the energy levels of these electrons and the clouds they can only give these certain colors so if you see lines at 65 36 5 6 nanometers you know that's a characteristic color of hydrogen and this is the one that you'll see all the images are colored pink if there's helium there it will give a different set of lines if you've got elements of mercury or carbon or nitrogen or neon or sulfur they all have a characteristic fingerprint in terms of the colors they admit and which of these lines which of these colors are strongest we can use not just for what chemical elements are there but ratios or specific patterns in these lines tell us the density and the temperature within the gas and so astronomers use something called a spectrum which is taking a light from the distant objects plotting against wavelength the intensity of these lines we have something like this here's the light from stars you're plotting wavelength against flux and you've got discrete spikes where it's Lotso just a tiny little band of color there's lots of light and those are from specific elements of gas atoms so here you got oxygen neon hydrogen lines oxygen and here's the very strong hydrogen line it glows pink so the reason I'm telling you this is that when we take a Hubble Space Telescope for example image it's not just like the camera in your digital camera we isolate light from specific bands so say I'm interested in how hydrogen is distributed maybe I just want to select this tiny bit of color and just pick out all those gas and try and pick out the light from just the hydrogen atoms then maybe I'm interested in the oxygen and I might take just that tiny little chunk of a spectrum and just pick out all the light then the oxygen atoms are giving off and that way we can deconstruct where perhaps the chemical atoms are and where certainly those ratios between the lines so for example here's a nice wide filter so we're isolating the light just in the wide green centered around sort of 540 550 nanometers pretty boring lots of stars let's take a blue image wide blue so wide filter again lots of stars not very different but then we take a very small filter we take a narrow filter centered on the red and this is where the hydrogen gas emits and funny all that you can see all the hydrogen atoms in this happens to be a supernova remnant here and then we colorize each of these black images and add them together and so the net result you colored thee the green one green the blue one blue the red one red you end up with a composite image which then recreates the natural colors and I will say that nearly all the pictures I'm showing you tonight are real images of space there may be one or two artists impression and I'll I'll try and remember to tell you about them the other thing is that a lot of the pictures I'm showing you I try to pick out ones that a natural natural color not quite true color but generally natural color and so they're colorized so things as a portion the wreck the correct color that they're emitted in so we can do tricks like this say here's a bit of a gas cloud I'm going to show you later as part of a supernova remnant and again I'll tell you about those later but we can isolate blue filter the light from oxygen atoms like from nitrogen atoms like from hydrogen atoms colorize them as we like stick them together and you merely get from the colors the distribution of the atoms within that cloud there are times that when we play a little fast and loose with the colors and that's especially true when we start getting right the edges of what we normally detect with our eyes you want to look at an image with your eyes you need to be able to see the colors in it so for example here's a beautiful nebula there's an image taking and wide green that's picking out the light from the stars we have an image of a returnee bit of red that picks out all the light from the hydrogen atoms in the cloud but then maybe we take an image in the near-infrared it's kind of off the scale it's over here it's not like we can pick up with our eyes so what color do we color it in our composite image we have to cheat a bit in that case we shift all the filters down and the colorizing maybe we say we know it's green but what we're going to do is we're going to color it blue we know hydrogen is really red but we want to color the infra red red so we just slip it down a bit make it a little bit sort of orangey red and then we can then safely color the infra red red and then combine the images to get this so what you think may not be accurate but it is a fairly faithful representation things we have been slid down the spectrum a bit but you see that still sea was bluer and what's redder and then you get your final image like this so most of the colors are representative of what we see now of course if you flew out there you might see colors approximate to this you'd have great difficulty perhaps seeing all the structures because you mix this light in different bands we can have long images that pick out the faint gas clouds short images that pick out the bright stars so we might play hard and fast with the contrasts to kind of accentuate the very faint structures and the other things if you try to look at this through a telescope you would have great difficulty seeing these colors with your eye because the cells in the retina that are sensitive to colors and sensitive sorry faint a few structures the rods are not sensitive to colors so it's always disappointing looking at these nebulae through a telescope because they appear just white you're not picking up the color and so relaxing and see them much better tonight on these images so let's go back to the science right we've had a bit about the images here's the Rosetta Nebula at the core is a young cluster of stars remember this is astronomy so young is 4 million years old they've collapsed down under gravity from a big cloud of gas and dust and what she sees surrounding it's the remnants of that cloud star formation isn't 100% efficient there's matter left over in the gas cloud once the stars are collapsed in the dense core and the light from the stars the energetic light from these stars is radiating the atoms causing them to fluoresce and it's mostly hydrogen so you've got this pink color also around the star cluster you'll see there's like a bubble they've got their own little cavity and that's because the star's heat up the gas next to them hot things expand and they create this bubble they're also energetic winds from the surface of the stars which eat away at the clouds as we'll see later and so all these star clusters you'll see they'll have the surrounding gas cloud and they'll be in their own little bubble and just a word about scale from one side of the rosette nebula to the other is 100 light-years now some of you may not be familiar with light-years despite the name it's a measure of distance is how fast so it's how far light travels in one year and there lies the fastest thing there is it travels at 300,000 km/s and it travels nine and a half million million kilometers in one year and we just call that a light year so it takes like a hundred years to go from one side to the other so don't think these are tiny little things around stars these are vast structures so we've got the stars I've told you about the gas the last ingredient is dust and by dust I don't mean like what you may find rolling under your bed at home it's not the dust that Philip Pullman has in his stories which is wood and what he uses to describe dark the idea of dark matter this is actual solid small solid particles of carbonates and silicates so it's like soot and sand and these particles are mostly tiny they could be about a thousandth the width of a human hair up to perhaps a few molecules across their little solid particles and if you like bouts about the size of particles and cigarette smoke they're tiny but if you get vast clouds of tiny particles they are there's enough of them that they can obscure any background light so when you look at this galaxy you can see the nebulae you can see the blue star clusters you can also see dark veins along the spiral arms that's not an absence of stars that's there's a veil in between you and the background light that's the clouds of dust blocking the light from the stars and that's mainly comprised within the plane of the galaxy so if we instead look at a galaxy edge on you will see that the dark layers of dust almost like cut the galaxy in two and I'll remind you that you live in a galaxy like this about halfway out from the center to the edge so when you look at your galaxy you're seeing edge-on like this and so if you see the Milky Way unlikely to see it like this from Cambridge especially if it's taken in the southern hemisphere it's slightly more dramatic because you're looking more towards the center the galaxy in the southern hemisphere just to guide the eye you can see the kind of shape of the galaxy there but I hope you can see there dark clouds even within our galaxy there you're seeing these dust clouds in the own disc of our own Milky Way fully with you know without any and birth telescopes binoculars in particular up here you have the Southern Cross if anybody is familiar with the southern hemisphere it's a very prominent constellation and right next to it is the coalsack Nebula again you can see this for the unaided eye it's a it's a big dark cloud that's blocking the light from the background stars so this dust exists in with the gas and it's more than that it's mixed in together and when you see a nebula you see not just the gas clouds radiating you also see obscuration by the dust so here is a classic nebula what you have to remember there's a big diffuse cloud around it you can't see it because it's radiating in radio it's invisible you only see the gas when it's close to a small star cluster and then it's almost like a little bubble little that's broken through the cloud if you like and you're looking into a cavern where the insight is lit up by the glowing gas atoms the glowing hydrogen so if we zoom in further you begin to see that there's dark shapes and this is where the dust is mixed in with the gas and it's blocking out the background light of the hydrogen gas and if we zoom in and even further you see some of these completely opaque clouds and these are the densest clouds in the interstellar medium I say dense for still a lot less dense than the air you're breathing now but the dust is mixed in with the gas and because we've got so much dust within these clouds no Tony doesn't stop the star light the background stars at the star light getting through to us it also stops the heat from those background stars from entering the cloud so the core of these clouds gets incredibly cold goes down to a few tens perhaps degrees above absolute zero and at those kind of temperatures the atoms in the cloud join up to form molecules and these are known as molecular clouds deep within these we have molecules not just of hydrogen that absorb see the most common or water come to outside carbon dioxide we got ethanol we got ammonia think of a complex chemical we've put a complex molecule we've probably found it out there in space and the other thing you notice but this is kind of looking a bit shredded around the edges it's fitting quite a harsh environment and that makes these molecular clouds suffer so dust we see it because it blocks out the background light now let's look at a very famous constellation if it were clear tonight you can go and see this in the southern sky hope you all recognize it as a Ryan this may be how you would see it with your na to die but if you then take a picture which is sensitive to all the hydrogen gas there there's lying in this direction about 1,500 light-years away from us you see the whole constellation is encased embedded in hydrogen clouds and if we zoom in to a region around Orion's belt there's a very famous no balonus sword but in a minute I'm going to look at this region here and then I'm going to just tip the image round on its side this is the Horsehead now for obvious reasons and when you're looking at the edge of a dust cloud here note there are more stars up here than there are down here that immediately tells you there's something obscuring stars behind here you see the edge of the cloud energetic light winds from stars are shining down they're making the gas glow and you can sort of sense it boiling off except to the point here where you've got a really dense pocket of dust there's kind of protecting the just this little little pocket from erosion from the star light star winds and that's the horse head and that resists the erosion and if i zoom in even further we look at this in detail this is what's known as the working edge that's where the impact from the winds and the irony's ionizing radiation from the stars eats into the clouds provides a nice sharp edge and already you can see perhaps the young star breaking out of this gas cloud there's gas and dust cloud that's going to be your first indication that this is where stars are formed you'll also notice that the stars that you see through the cloud are appear red the ones outside appear white and so dust produces an effect on stars it's the curse of astronomers any light that goes through a dust cloud is what we call reddened and as the light travels through the cloud the photons interact with the dust particles and it depends on the wavelength of the light the color of the light and the size of the particles but what happens is the blue light gets scattered by the dust particles preferentially the red light can just travel through the dust cloud fairly unhindered so this for example is why you see red sunsets red sun rises it's the particles in our atmosphere scattering the blue light and midday the Sun is overhead you're seeing it through the atmosphere maybe there's a bit of scattering but down at sunset or sunrise you're looking at it not just through more of the atmosphere and of course this diagram is not to scale you're looking through the denser part of the atmosphere as well so there's more of this scattering and only the red light makes it through the blue light gets scattered out of the path it's the same reason you see a blue sky but I just remind you what blue sky looks like I guess we didn't have one today when you look up at the sky you're seeing the scattered blue light so if I'm standing down here in the earth and I look directly at the Sun I see all the light from the Sun making it to me but if I look up in the sky I see all the blue light that's been scattered by the Sun beans going through other parts of the atmosphere so in the same way that the scatter blue light makes the atmosphere visible to me the blue light that's scattered by dust can also it makes the stars that you see through it appear red it also makes the dust cloud obvious so here you have a dust cloud I hope you can see this obscuration here dark patches as soon as it gets near this bright star it's lit up you see the scattered blue light near the famous Pleiades they happen to be living near or moving past some dust clouds these are blue ok the stars are blue but you're also seeing all this blue light that scattered off the clouds and here's one of my personal favorites this is the bright star Rigel and a dust cloud next to it and it's scattering the blue light it's called the witch's head nebula can you see her profile yeah knows math nice witch's chin so we can see the dust because it scatters because it absorbs and it also gives off its own light most of the images I'm going to be showing you our optical just going to show you a few infrared pictures so you recognize here you have the edge of a dust cloud look more stars up there fewer down here obscuration edge of cloud pink gas being ionized I'm now going to move to the same picture same region of space in the same scale you're now going to see it in infrared radiation because what happens is this light it heats I mean it's blocked from getting right to the core of the clouds the densest part of the clouds but it heats up the dust grains heat them up to temperatures of tens hundreds of degrees where they start to radiate not in the optical but in the infrared they're not quite warm enough to radiate in the optical and so you can detect the infrared emission from the dust grains themselves and suddenly all the dust structures become apparent she'll do it again I want you to look particularly round here and round here and you will see in the same way that I told you red light isn't affected by dust grains that means the infrared light is even less affected by dust grains so deep in here there are star clusters we can't see them in optical light but their infrared light can travel through the dust and we can see them there in the cloud it's true about external galaxies his beautiful Whirlpool shaped spiral galaxy you see the dark obscuration from the dust lanes if I click to infrared again you lose the stars and you just see the emission from the dust itself and here's the obstacle again of the Pleiades and if I move to the infrared again it becomes much more apparent the radiation from the dust and we're going to stick in the Pleiades for a minute here's the southernmost star Murrow P and I'm going to zoom into a tiny little region next to it and by next I mean it's probably separated about just over 3,000 times the size of our solar system okay so that's quite close and if i zoom in on this tiny region with the Hubble Space Telescope no the star Murrow peas up here somewhere out beyond the wall and you can see some of the scattered light from the star but this little patch of dust you can see it's been affected by the light and the winds from the stars it literally is if something's just gone whoosh over a pile of dust the lights of fluffier grains have got swept back more easily the heavier gains have resisted this this push sorry so you get the idea that starlight and star pressure as star winds can sculpt and shape and push dust around and nowhere is this more obvious than in this beautiful nebula called the Eagle Nebula it's not actually obvious from this picture why it looks like an eagle but if you zoom out of it it's more Eagle shapes now remember this is like a cavern in a big cold cloud you've got a young cluster of stars about five million years old their lights raiding an exciting gas lining the walls of the cavern you can see is that there are dark dust structures that are opaque now if we zoom in on some of these you can see they form these long pillars and the size of these pillars it's about 10 light years long from one end to another and the starlight and the winds are having an effect and eroding the dust and the gas but why do they always form those pillars you see that there are very distinctive long pillar shapes and you'll notice them a lot more in a minute and this is to do with the nature of the radiation and the direction it's coming from imagine you've got a cloud of different densities of gas and dust so here the darker pockets and then the dark bits meant to be the really dense pockets that resist the erosion the lighter fluffier stuff a lighter progressively lighter Gray's now I'm going to switch on some young stars high up above the ceiling the light is going to eat into the cloud progressively it should do it will eat into the cloud it erodes the lighter fluffier stuff much more rapidly and then the densest stuff acts almost like an umbrella protecting stuff beneath it and underneath that umbrella the stuff behind is not irradiated it's not eroded and you form these long pillar structures and so if we go back to this image you've already seen you can see it's like fingers always pointing in towards the star cluster all around the edge the nebula there in the rosette nebula there in the Eagle Nebula pointing in and in fact these 3 pillars are form one of the most iconic Hubble pictures that you see that's good where you've forgotten about views and ours I'm glad they're there and again these are light years long but even on the tiny scales you've still got that sort of protective pillars and they're all pointing towards the source of the radiation and the winds if we zoom in to the top here of this pillar you get a sense of the gas boiling off it's being lit up it's being ionized it's heating up it's boiling off the dust is getting swept off and away from the pillar and what's left behind are the densest pockets the coldest pockets and they resist this erosion and you can just begin to see them breaking free from the edges of the cloud just ringed a few to guide the eye and if you want to see what happens to them well we have to go back to Orion and look at those little sort of cocoon shapes at the next stage of development so back to Orion's belt there was the horse head nebula will go down to the great nebula and Orion's sword this is a massive region of star formation it's a huge stellar nursery and deep within there there's a cluster of stars let's move to the Hubble Space Telescope picture it just takes in a little bit of that nebula again think of this as a large cavity that's been excavated by the winds and light from these stars so again on the same scale in the infrared you can see through the clouds and you can see the young star clusters lying at their core and some of these are only a few hundred thousand years old very young and they're blowing and shaping the gas around them but if we close in on those stars or the full very obvious ones we see here now a little bit saturated I'll just change the contrast a bit so I'm not so interested in the stars I'm interested in some of the structures of the dust and you can perhaps see there are a few funny objects let's just ring them and blow them up those are those cocoons at the next stage of their development we think these are planetary systems in formation around young stars forming from these gas clouds here's a schematic I don't think I need to tell you this is an artist diagram though so if you have a large cloud of gas and dust it collapses under gravity especially where it's dense the Cert it's core and if things fall into gravity they heat up they gain energy and so matter rains into the core of the the cloud until at some point it reaches temperatures to say above 15 18 million degrees and a star is born and the process called nuclear fusion can begin that makes the star shine but again star formation isn't a 100 percent efficient there's lots of stuff left in that cloud around it that hasn't got used up in the star before it got switched on and because it's spinning settles down into a disk now this disk eventually we think goes on and forms a planetary system over perhaps the next hundred million years perhaps this is how our own solar system started four-and-a-half billion years ago with these objects in a Ryan we call them prop lids by the way short for protoplanetary disk we think we catch them in about this stage as a very young stellar object and it's surrounded by like a doughnut or a dust ring and again artist's impression I wish we had pictures this good of the prop lids but you've got a young stellar object and then you've got a very dense cocoon of matter around it including the obscuring dust so look again at some of these prop lights and Orion some of them are very conventional some are very misshapen and just to remind you that a solar system like ours we think was lucky was formed in a fairly isolated environment these little prop lids are forming right close to the strong winds and radiation of young stars and it's blasting them in particular if you look at the ones very close to the massive four stars in the center are just ring them and give you a sense of their direction they're almost like wind vanes being pushed out and there's a lot of argument among scientists about whether properties like this will eventually go on and form solar systems like our own or maybe just a reduced number of planets or a different kind of planets maybe some of the solar systems have very different kind of formation processes between the cocoon and the planetary system so I've told you how these nebulae are the places for star birth but they're also intrinsically associated with the death of stars and you get all kinds of stars out there you get yellow stars like our Sun lots of the blue stars that I've shown you in some of these star clusters and a whole of a star's life is a battle against gravity gravity wants to pull it in and the only way it can resist this is by the process called nuclear fusion at its core where it uses progressively heavier elements and obtains energy that supports it against eternal collapse so a star like our Sun will start by fusing hydrogen atoms into helium and it'll do this for perhaps up to 12 15 billion years of its life but at some point it's going to run out to the fuel where it's hot enough to do the fusion in the core of the star and at that point it's not hot enough to burn perhaps heavier elements and it can't any longer support itself against gravity and when that happens the core of the star collapses it collapses down now remember things that collapse down under gravity get get hot so the core of the star collapses down heats up and drives away the outer layers of the star and form something looking a lot like this now this is a planetary nebula it doesn't mean it's got anything to do with planets it's just the name the Victorian astruc books early 18th century rather astronomers gave them when they first started observing them in the telescope's because they were sort of round and disc II now here you're really looking at a bubble that's been thrown off a star this the famous ring nebula at the center here is the core of the star collapsing down to become what we will what we call a white dwarf it's heated up it's going to glow for a long time and it's radiation is exciting the gas layers that have been blown off the star causing them to give off radiation these are going to expand away into space over the next few thousand years and cool off and fade so these are fairly transit and transitory features what you may also have noticed within the structure here are dust obscuration dust structures and so this is and as well as some of the infrared observations shows us that we think the dust that we see endemic throughout these galaxies is forged perhaps in the late stages of a star's life when it when it before he goes ago this catastrophic collapse it swells up to come something called a red giant and the chemistry and the temperature in the outer layers of this is ideal for forming dust grains that then get expelled when the outer layers of the star blow off and there are mirrored so these beautiful nebulae this is a fairly conventional one it's about a Lightyear in diameter here's a much younger one about 0.2 light-years in diameter it's called a spirograph nebula but again the source of these weird structures isn't obvious and if you read about this in astronomy books you have a very conventional view the star cent goes crump outer layers go off in a nice expanding shell in practice it's rarely that beautiful of that simple here's a very strange planetary nebula it's got several bubbles it's got like eleven different shells it's almost like it's thrown off a layer of material about every 1,500 years and it's done at about eleven times and I'll content with that it's emitted jets and winds from the white dwarf to understand the end point of a star like our Sun is not as trivial as you might get you might think they're very complicated physics going on it's not in creating these beautiful structures and you don't just get ones like this you get even more complicated ones where they the emission the outer layers get him to get driven into a bipolar shape and here for example it's a beautiful peach from the refurbished Hubble Space Telescope it looks like the star at the core perhaps threw up and out of very dusty very dense layer maybe a few thousand years before and that's formed a doughnut or has been blasted back into a doughnut and the other stuff has been ejected it hasn't been able to go in that direction because the dust doughnut has blocked it and it's expanded and it's been shaped by this initial bit of dust and you get systems where perhaps they were and binary stars or maybe there were strong magnetic fields and the progenitor star you get very complicated structures and outflows but if you have a star that's much more massive than our Sun say above eight solar masses the end points somewhat more catastrophic it has it's hot enough to burn beyond hydrogen to helium in fact it can start fusing elements right up to iron at that point you can no longer get energy out and bigger stars more massive stars of the blue stars because they've got their more mass they've got more gravity they've got to produce more energy to resist that gravity they've got to burn hotter and physics hotter things are bluer so if you see a blue star it's a mass of star and not just that you know it's a young star because even though they start off with much more mass to begin with they burn through it it's such a prodigious rate they have lifetimes of only tens of millions of years and so if you see a blue star it's a hot star it's a young star it's a massive star and when these reach the end point of their lives when they finally have fused into iron in the core they throw off their outer layers and a much more dramatic explosion here's an example of one that was the suit the explosion it's called a supernova was observed by chinese astronomers in 1054 this is how it appears now these filaments of the outer layers of the star is still expanding wait about a thousand kilometers per second enormous ly fast and these filaments comprise not just the outer layers of the star but as they expand they sweep up the interstellar medium before them the blasts wait there's lots of energy in the blast wave it can excite the the atoms in the gas both the stuff that's thrown off the star and the stuff near to stella medium it all gets mixed up together it all gets compressed and as it cools it produces these glows and what we call these supernova remnants that glow thousands of years the core of the star to say in this case the core star collapses down and gets squeezed by gravity until such a point that even the atomic structure gets gets affected and Neutra and protons and electrons get squeezed together to form neutrons and neutrons don't like being squeezed and they resist it and that's when you have a neutron star if you start having a much bigger star or the original star was much more massive say about 25 solar masses or more then you can't store as stoll the inward pull of gravity and that's the point where you get a black hole so these supernova remnants usually mark the points where there are neutron stars or black holes these exotic objects the end points of stars writed look at the core and of course these are chemical factories you've got all the elements that were cooked up in the center of the stars during the supernova explosion there's a flood of neutrons that bathes all the atoms from these atoms can instantly transmute to much heavier elements than iron so a lot of the heavy elements are cooked up in the supernova explosion as well as been discarded from the course of the stars and these can get thrown out into space mixed up with a primordial hydrogen gas and seeds the gas around it with these heavy elements and this is important because those are the gas clouds that later go on to collapse and form new stars and so all the carbon and nitrogen and iron that's on our planet in our bodies has gone through this process of being formed in a star mixed up into a gas cloud that then later collapses to form our Sun and did the planets because all of this is going on for once at once and in the same region here's an example here's the star cluster you can see the gas cloud around it you can see some of these pillar structures there's one star in the edge here maybe this is the one that was the most massive it's about to go supernova you see it's kind of thinking about it's throwing a few preliminary layers thinking yep should I go supernova yep so that's about to go supernova very soon it's reaching the end point of its life but still within this cloud you have some of those very small dark molecular clouds waiting to fall together and form stars and you also have perhaps a couple of prop lids down here beginning protostars forming within a cocoon so all of this happens simultaneously in the same environment and one can affect the other and so for my final point I want to just talk about the process of star formation because I've told you there's lots of gas clouds in our galaxy they've been hanging around for billions of years why star formation still occurring and if you have a gas cloud of a certain size it might have little bits within it that are slightly denser than others so maybe there's a region here where the atoms the particles in the cloud are slightly closer together gravity is stronger the closer you are to something and so these pockets begin to collapse down under their mutual self gravity and gradually you might get condensation forming denser regions within the cloud and then these of course have a stronger gravitational pull and particles around them pull them towards them and you start a runaway process of gravitational collapse so you think yeah all gas clouds none of them are perfectly homogeneous they're not all perfect density some of them will you know why haven't they all collapsed of course not all particles are stationary anything that has a temperature that is an absolute zero all the particles all the atoms are just jiggling a little bit they're in perpetual motion the hotter the gas the more these particles are moving around so even stuff that's at ten hundreds of degrees above absolute zero the particles are jiggling all the time you're mesmerized yet I'll stop that and these motions this we call it the thermal pressure the thermal motions of the particles can resist can give the particles energy to resist the inward pull of gravity so any gas cloud or the given size whether or not it collapses to form stars it depends on the balance of these two physical processes okay I mean there are things like magnetic fields and rotation that might also inhabit in inhibit collapse so I'm very simplified idea here but if you have a gas cloud whether or not it collapses to form stars depends on the balance between the gravitational force wanting to pull it in and the thermal motions of the atoms that resists this force and if effect effectively for any one cloud that's the balance between density versus the temperature so if star formation is going to happen one of these have to change you can have a large stock and a large gas cloud and it lives out there in space for billions of years and what we call like an equilibrium state it doesn't collapse it's too hot perhaps or it's too sparse it doesn't fulfill the criterion for gravitation or collapse it only starts to collapse into stars if one of these two values changes now it's hard to change the temperature of a cloud suddenly no source of energy coming in things don't cool down fast the one thing you can change very rapidly is this density and if you just squeeze gasps clouds a bit you can increase the density maybe push them out of this equilibrium state tip them over the edge so they start collapsing to form stars and this again is going to happen remember you want the coldest and you want the densest places you're really looking within these dark dusty molecular clouds and as soon as you squeeze them give them an outside kick they start to collapse and you get runaway collapse to form stars within those clouds so if you leave a cloud long enough maybe it'll get a gravitational tug from another cloud or star maybe something will trigger it to form collapse but there are other external things which can accelerate accelerate this process the most obvious place we've seen for young star formation it's in the spiral arms of a galaxy whole clusters of young blue massive stars line spiral arms now I won't pretend we fully understand this spiral arms are a feature that we see in all spiral galaxies through the disk what we think is happening is that you have we call it a density wave a wave of compression if you like moving through the disk and as it moves through the disk it squeezes the gas just that little bit triggering it to form and collapse stars and where this density wave comes from again you might get another astronomer here and they may give you a completely different view of this is one of the things we were really not very certain about in spiral galaxies but perhaps it could be the fact that all the gas clouds all the stars in orbit around a spiral galaxy they don't all necessarily orbit in perfectly circular orbit slightly squished circles we call ellipses these don't all necessarily orbit in phase and you may get twisting and bunching of these orbits and you'd actually get an ellipse pyrrol shape from the squeezing of these different clouds and the proximity of these clouds and so we think that could be one place where you get one reason why you get these compression waves that travel through the disc causing collapses the star clusters in their wake and on a much smaller scale here's a young star it's anywhere two and a half million years old you can see if excavating that bubble around it from its winds from its light as it does so it pushes its pushing material back and if we move to a view for the new Herschel Space Observatory of this new infrared you can't see the star because it's too hot to give off infrared emission you see the light from the gas clouds and the dust around it and you can see that it's it's pushing back around the edges of this bubble and just hear there's a new star about to form and that has been triggered just by the squeezing of the winds and the light from the star but the final nebula I'm going to show you is where we see this happening sequentially across the nebula this whole cause and effect from dying stars - but new stars being born this is called the heart and soul nebula not quite sure which is the heart you might guess that that's sometimes you can see what they're on about can't always this is a mix just to confuse you all now this is a big of infrared and optical so the blue is kind of where the optical stars are the green and the red are in the infrared and they show you where the dust is the red is hot dust the green shows you the green dust I'm just showing you this because it's clearer where all the structures are the invisible structures within the cloud actually you have seen part of this nebula before there's a little region over here well actually just just zoom in and what I think is the heart so many they also it's the soul and we just look at this region here you have seen it this was the first infrared picture I showed you and again just to give you a sense for comparative scale if I showed you the the pillars from the Eagle Nebula to scale they're about that size so the picture and the rights taken with a spitzer space telescope that works in the infrared the picture on the left is taken with the Hubble Space Telescope you could have realized there's a bit of one up person ship between these space telescopes now when this Hubble image was released in 1995 did great acclaim fantastic image they were very pleased with it and it became known as the pillars of creation ten years later when this picture from spitzer is released they decide to call it the mountains of creation so here we have the mountains of creation you've already met them they're on the outside of one of these nebulae but if we map throughout this nebula we can see a time progression of causation and effect so right in the center of the nebula right at the very heart actually you don't see a lot there are a few sparse hot stars some of these are foreground starts so the really big bright ones are the massive stars now these are all that remain from the original collapse of stars from this cloud they were originally in clusters but you know so much has happened so much time has gone by all that all their cohorts have gone supernova and these are just the stragglers of the survivors the ones that weren't yet massive enough to go supernova however those clusters when they were born they had the gas cloud a lot closer to them they're lying there winds pushed on the glass cloud they pushed it away from them they squeezed the gas and they triggered a second generation either from the squeezing all from the actual supernova explosions could remember these are huge blast waves that ripple through the gas the combined effect squeezes the gas and causes the next generation of stars to form now these are still in fairly young star clusters so you can see that these maybe a few million years old perhaps four or five million years old and indeed when you look in the infrared around some of these star clusters there are a lot of prop lids information again poor little prop lids being battered by the winds and radiation from the stars but nonetheless some kind of planetary system forming around these stars but that's not enough because the winds and the radiation from these stars are now pushing on the boundaries of the current nebula and as I showed you from the first near infrared image these are squeezing the gas and forming the next generation of star clusters to be born these are still deep within the dust clouds they haven't broken free they haven't had excavated their bubble but these are the next star clusters that are going to emerge in this in this nebula and so you have a progression of at least three generations of star formation the first one triggering the second triggering the third through a nebula and you see the sort of generational effect within one cloud okay I have shown you a lot of pictures this evening I didn't know quite what I was going to get through them all they're an awful lot I didn't get a chance to show you I do want to stress that I have quite shamelessly pilfered all these images from work of many of my colleagues all around the world and all these images you can access on the web and in fact if I have inspired you to go and find out more about the science and beauty of nebulae I give you just three things but you could go and look at in your favorite search engine so the first one I recommend it's called Astronomy Picture of the Day and this is the one website that everybody in my department whether it's a highest professor or the lowliest secretary or should I say loves graduate student but I don't some of them are in the audience but that is the first website everybody goes to it'll have a picture about something about planetary geology or space science or some of these nebulae or distant galaxies from a range of wave bands so it's just a chunky little paragraph and very accessible text so that is a new picture every day it's been running for about 10-15 years there's a huge backlog of images then you can go and scroll through and you can do searches for your favorite nebulae the type of object everything like that second site I thoroughly recommend Hubble Heritage Gallery put those words into your search engine nuclei expose all the Hubble images the really famous ones some of you may be completely new to it again they give a very accessible page of text about again understanding the science behind what you're seeing and you'll find many of the pictures I've used have come from there and there are many more to explore either as well and finally the images I've shown you tonight well most of them have come from the Spitzer Space Telescope so there's a similar image gallery there that you can access but I will flag that many modern telescopes the new telescope the Herschel Space Observatory the Planck telescope the next generations Space Telescope all work in the infrared there will be growing archives of new images of infrared images for us to explore and I hope you have fun doing so thank you very much [Applause] when I was a kid I think we have the general impression that space was space it was all empty but it's clearly full of crud hydrogen and helium and soot and sand water and alcohol bit like Regent Street on a Saturday night and it's all blowing and it's all blowing and it's got implosions and explosions and there are births and deaths and it's all to do with the transmutation of elements the beauty of the image is that these space observatories have given us is just breathtaking but also I thought that the explanation that carolyn has given us is also explanation also breathtaking and it's rather satisfying because we started the series with likley Robert May and Frank will check explaining to us how simplicity in thinking mathematical otherwise has helped to explain our understanding inform our understanding of the universe we've ended with Carolyn telling us how the use of science helps explain the beauty that the ideas and beauty all interacts so very many thanks Carolyn now it's very much appreciated especially at five days of days can I just say some thanks for this series it was organized by Lauren Arrington Zuri Lionheart Phillip David and Jessie Homans it was supported financially as always by the over generous rich and King whose generosity is just beyond praise and of course it was supported by large numbers of people at Darwin college who muck in and make it all work so many thanks to all those people and this is 2011 next year is 2012 what's 2012 which is love quite a home team it's my last year in this role and I thought since there are so many fine speakers and fine academics and arrests in Cambridge we also give him a bit of a burst so same time next week next year I mean see here [Applause]

Channel: Darwin College Lecture Series

Views: 4,099

Rating: 4.8095236 out of 5

Keywords: Beauty of Nebulae, Carolin Crawford, University of Cambridge, Darwin College, Darwin COllege lectures, Science and beauty of nebulae, nebulae, vacuum, interstellar space, death of stars, birth of stars, Spitzer space telescope

Id: KdKvPFWWJIs

Length: 60min 51sec (3651 seconds)

Published: Sat Mar 07 2020