The Early Universe - Professor Carolin Crawford

good afternoon everyone and welcome to the early universe which is today's topic of interest I've spent an awful lot of time of my lectures discussing different aspects of the universe so for example we've had to talk all about that very first light of the universe the Cosmic Microwave Background that happened when the universe was only 380,000 years old contrast that now with the stuff that's in the universe around us again we've had plenty of lectures about individual stars about the planets around them the way the stars clustering galaxies and the galaxies themselves clustering clusters of galaxies today's lecture is an attempt to join the dots how do you go from that very pristine early universe with barely any features in it to the complexity of the universe we have around us today and you'll discover it's not a case that galaxies emerged just after the Big Bang fully formed but they take a while to develop and grow they're not all born at the same time and they're going to take on different manifestations as they grow and evolve to today's galaxies and in a way this part of astronomy is very much driven by the observations really it's a talk about observational cosmology and as I seem to say nearly all my talks this is something it's undergone a renaissance in over the last fifteen to twenty years and it's driven by the bigger the better telescopes that can achieve much fainter magnitude see much fainter sources the fact that they use adaptive optics so they get much clearer images and also our ability to image and the sky in the infrared which then allows us to see objects at further and further distance and it's still early days there's a lot we have to learn but we're going to talk about what we think happened between the cosmic microwave background to today's universe what are the first stars like what are the first galaxies lie what ones have we discovered and how exactly do you go about exploring that very distant parts of the universe and also of course what does it tell us about galaxies like our own Milky Way we know it looks something like this now but how different was it in the past what kind of galaxies ought we to be looking for so if we start at the beginning we're not quite the beginning I'm going to ignore the Big Bang right Big Bang happens universe in flights very rapidly and for that first sort of three hundred thousand years old it's a hot soup of charged particles and bright and energetic photons and it's all confined it's a bakelite can't escape the universe is expanding the universe is cooling and at some point about 380,000 years after the Big Bang it is expanded enough and cooled enough that all those charged particles all those protons and electrons start to combine to form the very first atoms now we call this recombination strictly it's not right because it's the first combination it's not a recombination but it is the recombination area and at this point everything that fills a universe it goes we're in completely opaque to completely transparent the universe is full of neutral atoms and the boundary between this kind of pre cosmic life and sort of pre recombination era and post recombination era is the Cosmic Microwave Background again this is just the picture I showed you from the planck satellite this is a temperature map of the whole sky and you have to realize that this is in fact incredibly uniform these are just tiny tiny little fluctuations the universe is incredibly smooth there are tiny enhancements in density which are producing these little temperature fluctuations and they've been caused by sound waves that were traveling through the universe at the instant that it called and the reason that this is the first slide of the universe is it's at that point the photons are freed up as I say before that point everything is charged the universe's are Paik photons can't ask crystallizes out to form the first atoms photons are then free and they travel through the universe towards us and those first photons we see other light to the microwave background that's why the light and the patterns in this light tell us what the universe was like at that time so it's clumped here you have to realize though it is not luminous matter that's clumped it's dark matter the first congregations are matter to form are specks of dark matter think about our ordinary matter luminous matter it's subject to lots of different forces that kind of resist it clumping together under gravity dark matter has no such problem with that it starts to collect simply under gravity and these tiny condensations you see in the microwave background art form the focus for those gravitational aggregations and they will start to gather into dark matter and it's only later on that we will see neutral gas start being pulled in and becoming part of these structures of course we can't see this happen it's dark matter nothing in the universe is luminous yet the best we can do about how matter congregates under gravity whether it's dark matter luminous matter is through simulations for example this is the illustrious simulation from about a year ago one of the state-of-the-art illustrations he is showing how Dark Matter pulls together under gravity to form the structures that we see and even this is only started in the universe is about half half a billion years old it's very difficult to probe this area of the universe what we do know from the simulations is that again that Dark Matters dragging the conjugations if you didn't have the Dark Matter there and structures and universe wouldn't have formed by today that nothing would have happened quickly enough and the other thing is that all the simulations tell us the ones that match today's universe starting from those initial conditions in the Cosmic Microwave Background is that structure assembles in a hierarchical faction fashion we call this bottom-up so tiny structures merge together to form larger structures as the universe ages but we do have a problem as I say about actually seeing this the universe may have moved a Paik too transparent there may be all these photons of the Cosmic Microwave Background flooding through it but it is dark it is full of neutral gas very dispersed it's just basically hydrogen smattering of helium all those elements that were formed just after the Big Bang and this is now what is known as the dark ages and they stretch from the point the microwave background to when the universe is probably a few hundred million years old here you can't see anything you've got that dark matter beginning to come gate starting to pull in the neutral gas and is somewhere in this stage that the first luminous objects will begin to form the very first generation of stars and we don't expect them to be like today's stars your go to imagine you've just got a sea of neutral gas neutral hydrogen again its primordial gas we think that the first stars formed be very much more massive than today's stars and parlays due to the fact that if you have a gas blob without heavy elements insert elements such as carbon nitrogen all the metals anything heavier than height these light elements are hydrogen here he's going to affect the gravitational pull within the gas and so it's very possible that when you've got a slightly filly a warmer interstellar medium that we have in current day galaxies the gas is warmer and it's getting is completely primordial composition you can accumulate a much larger mass into a clump before it switches on and it begins to shine so we have this hypothetical generation of we couldn't population three stars don't worry about the name but it's the first generation of stars and they click on at the end of the dark ages this is just an artist drawing of course I have to have to stress these are hypothetical the kind of masters we're talking about our individual stars with hundreds of solar masses worth of material in each star if you have that much material burning through nuclear fusion it's got to burn very brightly because of course the amount of energy it produces is what's cut you know counteracting the inward pull of gravity so the more mass you have or gravity you have the hot of the star has to burn them all rapidly burns through its fuel so this is a very transitory very short-lived generation of stars now maybe only live just a few million years and they're doing that very important thing which is they are forming out hydrogen and helium and they're turning into heavy elements at their core and when this first generation goes supernova and presumably enormous supernova events they then seed those materials into the interstellar medium around them the gas around them and then subsequent stars won't be as massive there'll be much more like the stars that we know about today that make up our galaxies today so these first population of stars are very very special so not only are they very more massive they are also that much more luminous and our problem is because we would love to see these first stars and we can't there have been dedicated searches but because they live such a short length of time they there's such a transitory feature that the chance of actually catching a glimpse of them is very remote and again you're looking for the light of even if it's a really massive star a very individual star all the way across the universe very very difficult to see but one thing we expect is that a very bright star will have quite an influence on the gas around it if you got a very massive star is going to be very Blues going to have lots of very energetic light that it's giving off and this light these photons are energetic enough that they will go and break apart those hydrogen atoms again they'll give the electrons so much energy that'll get stripped away from the whole atom and so we have the gas around the stars gets ionized again so it's been all hot and soupy have a cosmic microwave background then it's all neutral and then the heat from the stars begins to affect the gas around them so you'll develop a bubble around each star that will gradually expand and grow because it gets hot and as more stars begin to form and they get hotter and run through their lives these bubbles will begin to grow and gradually the gas will get less and less neutral and more and or an eyes de ghin this will happen around the first stars and then maybe the first stars will congregate into first structures and maybe these are proto guy lactic fragments they're not even proper galaxies or if you like they're kind of baby galaxies right in the early part of the universe and this effect will carry on and as these bubbles grow bigger they'll begin to overlap and so even though we may not see the first stars or these tiny first fragments we can perhaps trace when they're happening because we see this change in the gas around them I'm going to show you a simulation now it covers a two hundred million light year cube of the universe they've taken out the expansion of the universe I mean of course the universe is expanding all the time that we're evolving it but you're just going to see how these bubbles grow and overlap here all the white dots are some of those first condensations of luminous matter the blue shows you those ionized bubbles growing around them and where you see right where'd red and white is interface with a neutral gas which is displayed in black so as time goes on these bubbles grow they expand they overlap and the whole universe by the time the universe is a billion years old it has changed it's no longer dark and neutral we've gone through the dark ages and within in an ionized universe so dark ages end the first stars start to form and after that we get to the epoch of rihanna's ation and this lasts between say a hundred million years or a few hundred million years right up to when the universe as a billion years old and at that point those first stars those baby galaxies are beginning to grow and develop into things that we recognize as galaxies so by the time the universe billion years old as say it's completely different completely changed and those galaxies will in time evolved through the next sort of few billion years to the systems that we see around us today in the universe so an awful lot is going to happen how do you then see these very first gal these or even these protocol antic fragments I've told you about the first stars I mean we can realistic say we're not going to actually detect them there are possibilities that we can detect the change in the gas that they produce but let's look at detecting perhaps where they've congregated into early forms of galaxies and this is going to be back at this crucial stage when the universe changes from being a few hundred million years old up to about a billion years old things we can expect about these galaxies is they're going to be small and this is again from those simulations that model how galaxies build up you've got smaller fragments building up into bigger systems maybe they're going to have they have masses of about a million solar masses they're going to they're going to be physically small they're going to be faint not many stars are switched on and the stars that do switch on a very transitory you've yet to grow the more ordinary stars that have the longer lifetimes that are going to make those fragments shine for a long time so they're small they're faint and of course they're halfway across the universe which makes it even more difficult to see that light because as I say they're even if they were close to us there'd be small and faint it doesn't help they're a long way away and all of that effect gets diluted by the inverse square law to us and then there are further complications no any looking for very dim and distant objects but we have the redshift a lot has happened to the universe between when that light left that galaxy and got to us the universe has stretched and expanded and that is affect the light as its traveled through the universe originally what may have been sort of very blue light that was given off left the distant galaxy being hurtling across the universe towards us but it while it's making way across the universe space is stretching that stretches the light waves within the space and it keeps on stretching and it gets red shifted you stretch light you lengthen the wavelength of the light and it goes from blue to red and so this is the redshift we have to contend with the most distant objects are going to be the ones where the lights travel through most of the intervening space they've been stretch most and so they're going to their lights going to appear redder this causes problems first of all very distant objects may be going to be giving of most of their light in the infrared so we've had to wait for our infrared detectors and technology to catch up with what we can do in the optical so any recognizable features we understand about nearby galaxies have now been shifted to the infrared and what the part of the galaxy we see is the light that's given off in the blue now in the nearby universe the blue the ultraviolet light the stuff that doesn't get through our atmosphere is the stuff that we don't we've only recently begun to image in galaxies so we don't some understand so much about the blue light of nearby galaxies yet that's is what gets shifted into the optical with the redshift and we're comparing you know different parts of the galaxy in different bands of light so the redshift is a further complicating factor and then redshift also is tells you something about how far away these objects are so it is a bit of a nuisance shifts all the light to the red confuses everything but it gives us a good proxy for how far away these objects are the further an object is the more its light will have been redshifted but I'm not really going to talk in terms of redshift but you can think of translation between redshift and distance there's an even better one is that we use which is a translation between redshift and time if I ever see of galaxies here all of them light different distances away from us so just looking a patch of sky there may be some systems which maybe a couple of billion light-years away that means the lighters left that galaxy 2 billion years ago I'm seeing that galaxy as it was 2 billion years ago elsewhere in the same picture maybe one of these blobs I've got an object that's 9 billion year light-years away I'm seeing it as it was 9 billion years ago so this we can turn to our favor because the time that it takes galaxies to evolve and change is so much longer than any human lifetimes the best we can do is look at these different epochs these different snapshots and back through time and compare different galaxies so any image like this and you're going to see an awful lot of light like this within this talk you're looking at different epochs all at once you can unpack the layers and you go from galaxies it is seeing where it's a few billion years old out to five to nine billion years old and the ones that we're really interested in are perhaps the most distant and the most redshifted that are farthest away away she also means that the youngest because we're seeing them back when the universe with a fraction of its present age so redshift transcribes the distance which gives us an idea of how far back we're looking at these galaxies when they're light left them and another way we can look at it is also recall it in terms of look-back time so any one galaxy you know women with these frames I've got the look-back time so how far apart in the past I'm looking back and it also tells me what the age was of the universe at that point and of course it isn't a beautiful kind of one-to-one relationship this for example is a pot of redshift against in a fractional age of the universe the universe is 13.8 billion years old by redshift of one the universe is already a half its present age when the universe was 380,000 years old at the Cosmic Microwave Background the redshift was about a thousand and by the time you get to it being about a redshift of perhaps six and 12 that is the period between about 500 million years old two billion years old that's the dark ages so that it's very easy to observe this kind of part of the universe out to redshift of one we can't see this part out here where it's so far away today's talk is going to concentrate at these kind of red shifts between three and six and with sampling this kind of part of the history of the universe when it was about ten to twenty percent of its current age so you got redshift got distance we've got look-back time got age the universe all really equivalent and I'll try and be clear about what I'm referring to when in the talk okay so how do we go about looking at for very distant galaxies well one of the best strategies is to just take an image like that within the sky and look at the distribution of galaxies as with age this is our prevalent to doing a geological core drilling sample and some of you may have seen some these images they called the Hubble Deep Field so the most famous most celebrated of these images they've caused many other teams have done similar views out of the the galaxy and what you do is you pick part of the sky here's a familiar part there's the saucepan the Great Bear and I'm just going to zoom in and show you how small a region you get with one Hubble Space Telescope field you cover a patch the sky that's 124 millionth of the area of the whole sky and you stare that piece of sky for a very long time and what you get is a Hubble Deep Field now this is the first one it dates from about eighteen years ago almost 20 years ago now and it is again one of those snapshots where you've got foreground galaxies middle galaxies and then very early galaxies all within the same image you've seen them all of those different epochs and by comparing galaxies at different epochs you can start to build it you know join the dots between the very early sources to the nearby sources and not just that if you stare for long enough there is the hope that you might begin to see those very first galaxies now this was breakthrough when it happened it was followed a few years later by the Hubble Deep Field south which actually doesn't look all that different and that's a good thing okay because the Hubble Deep Field north which is the first one it was chosen to be looking out of the sky in a direction where there's not much of the Milky Way in the way it's trying to take a very clear view out of space there are maybe just a handful of Milky Way stars for example I can see one there they're just in the foreground but then you've got to worry you've spent ten days staring at this tiny bit space you put all your effort into that one little bit of space what if that's an unusual direction so if you then choose another direction out through a completely orthogonal part of the sky and it looks very much the same that means you have the heart that your one observation you're very deep Uggs is very representative and this is indeed what we call the cosmological principle that the universe when averaged out is kind of the same in all directions there's no preferential direction to the universe and even so all these objects you see nearly every single one is a galaxy there are so many within this field but still there's black space between the galaxies there are not so many that they're overlapping and filling the sky the still dark space between the most distant galaxies and then this was followed up a few years later by the Hubble ultra-deep field and this is an even smaller patch to the sky and it was looked at for about a million seconds it's about 11 days straight and again just to stress the area of sky imagine you've got like a one millimeter grain of sand and you hold it at arm's length and you look at it that's how big an area of sky this is and within this image there's something like ten thousand galaxies right pity the poor graduate student had to count them all and again we're interested in the look-back time but even just the number of galaxies we see and if that is typical of the whole sky that's Amelie telling you you've got of the order of 120 billion observable galaxies out there of course there could be plenty more and when you look at them there are some very interesting sources a lot of those intermediate redshift ones so here for example you've got a galaxy it's about a billion light-years away and you can see a variety of morphologies again you've got some that look sort of fluffy and spiral and then you've got some relatively compact and red ones and then you as you'll see later we've got some very strange beasties but within all these galaxies these kind of intermediate redshift ones there are plenty which are a lot older and there are plenty which date from before the universe was a billion years old so you're looking back about 13 billion years and then you're looking at that it's not quite in the epoch of realisation when those first galaxies are forming but you begin to see the galaxies that emerge and here for example are 28 of these galaxies effect I can't remember something like 50 of them within the Hubble ultra-deep field which date from before the unit book they date from the time when the universe was about billion years old or younger and of course you can see that all red they've been red shifted and I hope when you see these little blobs you begin to appreciate the difficulty of actually getting data on very distant objects it's not enough just to find them but then you're getting so few photons and they're all very red photons it's very difficult to perhaps characterize the source in terms of its size or as properties or its light and imaging is a very effective way of doing this because you can collect the light from a whole number of sources in one observation and then you would image through various bands to see how the light changes and very clearly here by looking preferentially at the red objects already you've got you're assuming that these are the most red shifted ones the ones that are going to be most interesting to follow up if we look for example right in the corner here and zoom in there's one of the faintest objects within this source within this field but you've pretty struggling to see it at the back okay probably need a Hubble Space Telescope from the back row to even see it you big again appreciate the difficulty this is well you can see its telephone number there udfy-38135539 this is one of the faintest objects one of the most distant objects within that field it's dating from when the universe well it's the look-back times thirteen point one billion years the universe was seven hundred million years old at that point this is probably one of the first galaxies to be emerging from that epoch of realization it's probably got the light of about a billion solar masses and it's Kotani okay it's probably a fraction of the diameter of the Milky Way now this is about as far as we can get back with the current technology and with the Hubble Space Telescope again just to stress from this ultra deep field you've got foreground galaxies and the ultra deep field only goes back to a distance of about a few hundred million years old we are not yet sampling that epoch of the first galaxies and the first stars and it gets even more challenging to do so so be aware that these are already fairly fully formed systems you can of course push the observations still further going back to a smaller region even within that Hubble ultra-deep field you go to the extreme deep field you image it in even more colors and even within this much smaller region you're still looking about 5,500 galaxies and you can incorporate UV lights you can incorporate UV and sorry object infrared light and you can get an even more slightly comprehensive image but you're still not getting many more galaxies but there is an advantage to getting this same image in lots of different colors because you need the redshift to know exactly how far away an object is but it's actually quite difficult to get if that object is so faint it's not giving off many photons together ideally to measure a redshift you need a spectrum it features like emission lines or absorption lines within that spectrum you can measure them and calculate it exactly that's not always possible for some of these sources because they're so faintness so far so for example here's one of the faint objects within this field you can't see in the main image and in the visible it doesn't show but it's light is so red shifted that it begins to pop out becomes more dominant in the infrared now if you have sources like this where you can't measure a redshift it would just be prohibitively expensive in terms of telescope time you can still get an estimate of its redshift from using its colors and let me explain this this is wave estimating redshift here's an icebox and elliptical galaxies in the current universe you can see it's quite whitey yellow it's full of old stars it doesn't have much in the way of massive star formation massive stars produce blue light it's only got old fairly small all stars puttering away if we distribute the colors of this galaxy into what's known as the spectrum you will see for example here you have it against color it's got lots of red light because that's the color of the stars it's barely got any blue stars so this spectrum drops down and there's any barely any blue light ok that's in the nearby universe but imagine that whole spectrum shifting to the red as the galaxy gets further and further away you can start to use things like the steep drop of light to guess what kind of galaxy you're looking at you can't get the speck from the object but imagine you just took you took a measure of how much light it has here how much light it has here there there there and you just get kind of a broad-brush spectrum and that's what we do is called photometric redshift fitting so in other words it's color redshift fitting and to show you here here's your galaxy in the current universe lots of red light so imagine we've got an eye band so that's the infrared you've got red green and blue it's got lots of light in the infrared in the red green not much light in the blue the spectrum shifts to the red as the galaxy gets further away and what you will notice now you barely get any blue light the green light has dropped enormously the red lights dropped a bit and the infra red stays the same shift your galaxy still further you begin to lose any light from the green filter and are you much reduced in the red you're beginning to forget reduced in the infrared so you can build up models you have the spectrum the galaxy of current nearby galaxies you shift it to the red you predict what you would see through the filters of your observation you match it then to the colors you see of the objects and you can start getting a first pass of how redshift did that object is yeah funny it were that simple because of course in the nearby universe we don't just have elliptical galaxies we also have spiral galaxies spiral galaxies from lots of red light and and lots of blue light particularly if you look at its spectrum they don't have that deep fall-off in the blue remember they like to go galaxies lots of red light and then it crashed the spiral galaxies' the blue light keeps on going and so they'll give a very different signature as they shift towards the infrared they won't lose the blue light so much so again you have to take a guess is is it a spiral is it an elliptical galaxy what do you predict so you do different model spectra different red shifts you match to the colors and this is a very good way of guessing the redshift so here for example this objects called Z 8 GN d5 296 now this is the furthest confirmed galaxy it's at a redshift of 7.5 1 you're seeing it with the universe we're looking back 13 point 1 billion years ago again about 700 when the universe was 700 million years old and this was first found and identified through doing that broad-brush fitting identified as a candidate and then you go and soak up lots of time on it with a bigger telescope to get the spectrum of it and determine the redshift so it's very difficult very time-consuming but you can pre-select the pre-screen your images for the candidates that you then going to follow up because you think they're a great redshift and in this source in particular we think it's forming stars at about 300 solar masses a year it's changing very quickly it's already got some heavy elements you've already had that first generation of stars turn the hydrogen to the heavier elements and it's got a mass probably between one two percent of that of the Milky Way so it's still quite an early system and here's an artist's impression of what it might look like if you went there now here we're detecting galaxies that are very blue and the other thing of course is that you can see an early galaxy may not look like the ones in the present day galaxies change and evolve so we might have templates from modern-day galaxies that are not applicable to the light from distant galaxies so this is quite quite a fraught way of determining your distances to the objects other things you can do if you've got lots of star formation maybe you're exciting the gas to make it glow you're producing emission lines for example if you see star formation in the nearby universe surrounded by gas clouds these the nebulae now in the visible these radio very strongly in the pink due to again hydrogen is the most common element you've got this line called H alpha it's six 656 nanometers it's a very pink color if I showed you the spectrum of a star formation region like this you've got the light from the stars it's very blue but you've got a huge amount just at that pink color now this pink color doesn't help us much because even if you've got stuff formation a great redshift it just gets shifted to the infrared or more difficult to detect but other light gets shifted into the visible so another strong line that you see in the ultraviolet is called the lyman-alpha line again it's produced by hydrogen gas around stars here it is weak continuum very strong lyman-alpha line and if we're dissing enough galaxies that gets shifted into the optical so imagine you've got one of those early systems it's forming stars but there isn't actually many stars there yet so you don't have much of that sort of background continuum you no lie to all different colors but you might have a very strong emission line spike may be due to gas around the stars absorbing the energy in reradiating it's lyman-alpha now you've got to get to redshift above 2 before that line gets shifted into the optical but again imagine you're doing different filters select your filters so that you've got one that just covers where you might expect the lyman-alpha line to emerge so de reg of two-and-a-half or three compare it to filters either side and maybe if you see you look in this color range this filter see nothing this filter see nothing but just in this band pow lots of structure maybe you're picking up one of these gas clouds indicating early systems and this is what is done here's a range that have been detected by the Subaru telescope in Hawaii where the green is picking out lyman-alpha clouds they go by the technical name of lyman-alpha blocks and these are just huge gas clouds that have been lit up maybe from star formation inside here's the largest known one again doesn't look that aspect that's that's bigger than a galaxy would be at that age it's kind of three times the width of the Milky Way this has probably got proto galactic fragments and the stars from those illuminating a wider cloud so we're seeing very peculiar systems out there you can also extend this you know if there are features in the spectrum where not just they're sort of massive spikes and you pick that flux of light maybe there's a sharp drop in the spectrum if you are lots of stars surrounded by neutral gas clouds what happens at 91 nanometers sorry 900 and ya know I think in angstroms I'm astronomer sorry hundred nanometers but 912 angstroms you get this you get this attenuation where the gas absorbs all the energy of the star so if you have very Rimmer if you've got lots of energetic photons they will get absorbed by those hydrogen atoms and so with the Starlight you've got lots of blue light and then beyond a point these are the more energetic photons and they get completely absorbed by any surrounding clouds and so and again this is a feature that gets shifted by register to 3 it moves into the visible so you've got the sharp drop in the continuum again here's your model galaxy at the redshift of 3 you get this sharp drop observed now imagine you image it in this band you image it in that band you've got a huge jump in continuum huge jump in their structure so here for example look at an object a new band see nothing look in the B band pow suddenly there's continuum light from galaxies and there are needs so many of those very obvious steps in the light from a galaxy these are called alignment break galaxies because this is the Lyman break feature and this is a very good way of identifying galaxies above a redshift of 3 or even higher if you move from the U and B bands up to the redder bands such as the R and the iron into the infrared there's always the worry though that we are detecting the most exotic gal seeds at high redshift we're only detecting those that are maybe forming stars at a certain rate are they representative of the rest of the galaxies out there how do you select a random galaxy and here's where you have to have some luck instead of going out and searching for ones that show a lot of continuum emission or we're assuming something about star formation or about the gas it excites to reduce that line emission let's just see if we can find some by chance and here we can make use of nature's own telescope gravitational lensing to remind you if you have a large mass like a giant cluster of galaxies it bends the shape of space around it light ways rays traveling through that space get warped get curved and get focused towards us if the geometry is right so the light from a background saw so the cluster wasn't there would travel straight towards us if you have a large mass like a galaxy like a cluster of galaxies in the way there's so much distortion all the light rays that would have gone off in other directions get bent round and get focused towards us this means that distant galaxies can be magnified because all the light that would have gone in those directions has got poured round towards you so they get brightened and they get magnified because these images are also smeared they don't look like little galaxies but like arcs and rings for example here's a cluster of galaxies able to 744 many of these Blues structures are the distorted mirages of those background galaxies once it just happened to lie behind the like you know in that direction of that cluster if you look at these images of the distant galaxies you were looking at galaxies behind the cluster and again you would the the spectrum the colors of the distant galaxies and not affect by its gravitational lensing process so the spectrum is unchanged you can use the colors to work out the redshift so for example in this cluster if you look at some of those tiny images between the galaxies there's a very distant object again you have to have the either believer to believe it's there so this what I mean by it's really the observations to get to these distant objects but here again you've got incredibly distant object it's probably about five hundredth the size of the Milky Way it's probably only got a mass of about 40 million stars and it's you know without that quirk of cosmic geometry of putting that cluster the galaxies in the way it'll be ten times smaller it be ten times fainter we would not have a hope of being able to observe it and indeed they can fate for the farthest known object and this is just from its colors we haven't got a spectrum of it it's too faint to get a spectrum of it is this object max oh six four seven jd1 it's an estimated redshift is and would put it at an age when the universe was 430 million years old so this is right within the realisation epoch this is an incredibly exciting source this may be the most distant galaxy I can show you the sieve and this afternoon but we're not going to know much more about it for a while so what do we know about these distant galaxies especially the ones say above a redshift of 3 just before the epoch verrano's ionization so you're not seeing the first galaxies but you're seeing early galaxies well obviously they're smaller and they're fainter we expect that that fits with this idea of assembly of smaller structures up to make bigger structures but they also have different morphologies some of them look like spirals perhaps you might believe that when is there's one up here some of them look like ellipticals but there's a higher fraction of disturbed sources blobby disturbed galaxies they're only about sort of ten percent than the local universe by the time you get out to Richard 3 and above you're looking at at least 25% of them consistent with you again the idea of assembly of small structures to form big ones and indeed in the Hubble ultra-deep field you get many of these kind of tadpole-like galaxies or Lego galaxies where small you can begin to see fragmentation or other small fragments joining together to form bigger systems but we are still limited in that we can perhaps start to get these gal sieze but we're not sampling this region to do that we have to not look for the emitted light but we start to look for almost like the shadows that the gas might cast and background light we're going to look for absorption now one thing we learn from the simulations from the observations is not all galaxies form at the same time some form earlier than others and indeed one of the very early manifestations of some systems is a quasar this is when you've got a galaxy the supermassive black hole Center it secreting material the activity at the center outshines the local galaxy and is so bright you can see that light halfway across the universe now as that light travels across the universe it will travel through clouds of matter it will get some of its light absorbed from those clouds of matter so here's your distant quasar maybe you got invisible clouds a neutral gas maybe you've got very obvious galaxies and every time one of them crosses this line of sights distant quasar they're just absorb a bit of that quasar light and you get signatures of invisible clumps of matter along the line of sight so to explain spectrum again this is lyman-alpha emission lyman-alpha again hydrogen gas emission at the quasar it gives you the redshift of the quasar and then you've got the rest of the light of the quasar which if it all came to us would just carry on cording to this dotted line but instead every time that light intersects our clouds along the gas cloud of Gathol on the site that gas just takes a little bite out of this spectrum to give one of these spikes and remember they lie between us and the quasar so they're at that all these absorption again happens at lyman-alpha but they're not as redshifted as the quasar so these all intervening clouds all produce spikes of absorption at lower redshift so you can see there nan up here there are loads down here this is the lyman-alpha forest you can see that in many distant quasars and again the further the quasar these features year the the absorption line so near is the quasar emission line red ship the quasar redshift are the ones that are higher redshift further back in the history of the universe and you can look at the distribution of these neutral gas clouds with time back to wherever that quasar was and the first thing to say is they're not galaxies they're not dense enough the clouds that are producing this light or not dense enough not massive enough the distribution is different from galaxies if you look around a quasar you don't see the galaxies that are doing the absorption these are likely protocol active fragments just big clouds well again we don't really know how big but they're the large clouds of neutral gas maybe some of those fragments coming together and forming the early galaxies what we do know is there are many more of them in the early universe than there are in today's universe here's about the lowest redshift quasar we know about here's a very distant one look at the difference in the lyman-alpha forest this has intersected many clouds of gas as the lights traveled towards us this is barely intersected any so we know that these clouds are much more numerous within the early universe and they begin to disappear to today's present day universe that's why we think there could be those either they get drawn into pre-existing galaxies or they form the clumps that then condense down and then merged form the galaxies so this is a key indication of the distribution of the gas right out to some of those throughout that ionization epoch and again looking at the properties of this forest and how it behaves can help us trace perhaps that point where the gas goes and from rihanna's to neutral again or rather I'm going the wrong way from neutral to reown eyes again it gives us a way of sampling because with one of these spikes you can work out something about the density of the gas you can work out something about is velocity how much mass there is pulling it together and there's going to be some dark matter there to just congregate that amount of gas together into one coherent clump and you can also tell something about metallicity of it and I'll come back to that in a minute but these are mainly due to gas fragments as I say we don't know how big they are very rarely you might have two quasars close to you know in the sky and there's one cloud that happens to bloat block both their lines of sight towards you then you can get an estimate for how big it is but you don't know whether it's one coherent cloud or maybe there's a group of them ordered about the same distance from you so sizes of these clouds are very difficult to obtain so here's a lovely animation trying to explain or demonstrate what I'm showing you we've got our quasar without any intervening meter this is what the emitted light looks like now as the light travels across the universe is going to get shifted all of these features are going to move to the right and every time the light intersects one of these blobs of gas is going to check a trunk out of the spectrum and see how this accumulates and how it builds up and again remember the Knik ones nearest Lacroix's are caused emission lines closest to because absorption lines closest to the quasar redshift and it all builds up and we can you know find so much about these gas clouds from this technique so I'm just going to go back says one thing I don't know if you notice we intersect the galaxy as we went along that's when it got interesting as the galaxy comes into view is a much thicker line of sight through a cloud of gas and suddenly we have a huge chunk taken out and there was some more features up here because every so often you get a patch of gas that is so thick that it absorbs all the quasars light these are called damp lyman-alpha lines it goes to zero if i zoom in around that region and then move it to the take out the redshift it goes down to zero just at that point there's so much light it's taken out all the crazy I'll spectrum to produce that much absorption you're looking at a very thick cold slab of gas again we can't find evidence for stars at that redshift so it's not luminous so and the sizes and this is going to be much bigger than the Milky Way so the things still collapsing down together maybe not luminous yet not producing stars so these perhaps give us indications of some of the early forms of perhaps the spiral galaxies' what we do know though is that here this is hydrogen absorption do the lyman-alpha you see at exactly the same redshift elsewhere in the quasar spectrum if you've got that galaxy causing this complete a pay part here they're associated lines from elements like carbon and magnesium so some of these systems even though they have got lots of luminous star formation they have been enriched they've had that first population of stars they've had that first processing of hydrogen helium two the heavier elements so what do we know the early galaxies are smaller they're less luminous they're probably forming from neutral gas clouds they're building up and again as I say a lot of them a blobby er than others and you start with galaxies at far redshift like this they still got to grow to todays galaxies and this is where still a lot of the uncertainty comes in because galaxies don't sit in splendid isolation all through their history they can accrete gas they're in large gravitational potential they're going to pull in primordial gas intergalactic gas they're going to continue to accumulate it from their surroundings so you're going to have an inflow of gas all the time we know that galaxies merge and you've got this sort of galactic cannibalism going on so they may be pulling in small galaxies and so you can either have primordial interstellar or intergalactic gas gradually accumulating and then you can soar up a small galaxy and you've got loads of stars and enriched material it's possible that looking at abundance gradients in some of these very distant galaxies begins to tell us when each of these process and might dominate or what might be important for the growth of a galaxy alternatively we know you've got a quasar you've got a supermassive black hole occurrence at early stages of the galaxy you've also got lots of very early star formation going on there may be points where there's so much energy put into the heart of a galaxy it'll heat up the gas and remember it's cold dense gas that collapses down to stars you heat up the gas it's not going to form stars any more so you're going to stifle star-formation heat it up enough it becomes it blown out of the galaxy so you've got these two competing processes of accretion and expulsion of gas and a lot of our current understanding about how galaxies go from redshift of three to the present day depends on modeling those two competing mechanisms and again you look back to redshift of one where the universe was half its present age well really you still got ellipticals so you've got little red galaxies and then you've got more kind of blue galaxies and the red galaxies they're shaped like lipped achill they're read like ellipticals they're just smaller and we think they kind of grow passively maybe they create material maybe you start with something that has merged maybe goes through a quasar phase but by the universe you know when the universe is getting on a bit it just settles down to a nice compact ball pulling in material gradually and growing passively to the current day we also see very distant blue galaxies spiral galaxies where the rotation has been measured at high redshift they're not rotating so fast they're not nice flat disks yet they're still settling down they're still undergoing a lot of star formation activity there's a lot of debate about whether the blue galaxies can turn into today's red galaxies and indeed if you look at a snapshot of galaxies that we think will grow into ones like our Milky Way we see that they change a lot through history of the universe in terms of both the way they accumulate mass they accumulate size but also in their colors and colors of course represent very active star formation periods because young stars massive star formation is blue you don't get that in the elliptical galaxies they stay red and they just low mass star formation they don't go and undergo anything spectacular but a lot of the galaxies and this may include the precursors to those elliptical galaxies undergo a huge burst of star formation you know eight to ten billion years ago if you just average up the colors of galaxies at different epochs back in the universe's past we find the redshift of one to two so here blue color stands as a proxy for massive star formation because massive stars produce blue blue light this is Jesse if you like the volume average star formation rate against you are here going back in time it's a huge burst here between eight and ten billion years ago and then the galaxies quiet and down and everything I so what happens here why is it so crucial here how typical is that for all galaxies or is it just the brightest ones that we're detecting are the nearby ones it gets a bit uncertain here because of the paucity of galaxies at much higher redshift there's a lot we've got to do to map these states is this the point where there's a massive star burst that expels the gas that it stifles the star formation you know what at what stage is what thing having an influence and subsequent evolution of the galaxy and what does this mean for our galaxy well obviously it's a spiral galaxy you look at it in the sky resembles something like this if it's like those other galaxies well first of all we know it's accreted small galaxies do satellite galaxies during its past but it's regular shape means it's never undergone a major merger so we haven't pulled in equal sized galaxies so we've been fairly quiet about obtaining matter that way however is likely still to have accumulated a small amount of stuff from satellite galaxies and from its surroundings and certainly if all those galaxies we look back in past epochs or anything to judge by eight to will have undergone an intense bursts of star formation eight to ten billion years ago and that's when a lot of the structure of our galaxy was formed and you know the ball and the major shaking at the core of our galaxy and before that well that's when it would have been those neutral gas clouds that we can never see except you know if you're an observer in a very distant galaxy far away one of those lyman-alpha clouds along the line of sight to another quasar maybe that has in the intervening billions of years collapse into a galaxy and are in that galaxies some life forms looking towards us they'll see us back as a lyman-alpha cloud in a distant quasar spectrum to the to us so what I hope the future we're slightly stymied at the minute but there's going to be a big change you've got facilities like Alma coming online Alma's very sensitive it works in the millimeter wave band it's very sensitive to the gaseous regions of the universe the cooler regions of the universe some of those very early star forming sort of objects those particular antic fragments as Alma gets more and more dishes online we're going to start being to probe those very dusty obscured star formation regions in the early universe beyond that of course from 2018 we've got the next generation Hubble Space Telescope this is going to be working entirely in the infrared ideal for those most distant galaxies at that point that's when we start to get redshift of some of these most remote targets that we've identified from the imaging of photometric redshift fitting and it's not just the James Webb Space Telescope there's a new generation of telescopes we just had to go ahead for the European extremely large telescope which should come online of the operation in the early 2020s and there are other initiatives like the 30-meter telescope in the States so there's lots to look forward to and we're going to carry on pushing back those boundaries and hopefully begin to study in great depth those contents those very early galaxies and you never know begin to see the very first stars in the early universe thank you

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Keywords: gresham, gresham college, gresham college lecture, gresham college talk, gresham lecture, gresham professor, astronomy professor, science, astronomy, cosmology, astrophysics, history of the universe, the universe, the big bang, the dark ages, the early universe, star formation, stars, early galaxies, early stars, carolin crawford, professor crawford, professor carolin crawford#, Chronology Of The Universe, Universe (Quotation Subject), Professor (Job Title)

Id: SKaUX4oWE_w

Length: 56min 13sec (3373 seconds)

Published: Wed Feb 11 2015