Development of galaxies by Richard Ellis

so good evening and welcome to the 2015 Darwin College lectures which this year are on the broad theme of development and I welcome everyone here in the lady Mitchell hall people in the overflow halls who are viewing on the video link and also there many many thousands of people around the world who watched these lectures later on they are freely available on the web Darwin College is 50 years old founded as the first College in the University of Cambridge exclusively for graduate students and moreover the first mixed college from a small beginning we are now amongst the largest college with an alumni body encompassing every subject and spread right around the world it's a very real example of successful academic development the third lecturer in this xxx series of weekly Darwin college lectures is Professor Richard Ellis in 1993 after a distinguished career that led him from UCL to Oxford to Durham he came to Cambridge as plumie and professor of astronomy and experimental philosophy since 1999 he's been the steel professor of astronomy at Caltech the California Institute of Technology if we go back many centuries Galileo's academia del enjoy was the Academy of the Linksys the farsighted ones and Richard Ellis today is at the forefront of Galileo's farsighted successes Galileo's telescope had a 37 millimeter objective riches as I understand a 30 meter mirror that's quite some advance he looks to the very edge he has brought major advances in understanding why galaxies are grouped into the Hubble sequence and for using gravitational lensing to find some of the most distant objects in the universe now Richard Eris has two rather nice connections with Dharan college firstly he was awarded the highest honor of the Royal Astronomical Society their gold medal in 2011 an honor in which he was followed the following year by our own fellow professor andrew fabian secondly his Cambridge chair the plumie improvisation was once held by Professor Sir George Darwin whose house forms the core of Darwin College Sir George helped advance understanding of the moon and the birth of the solar system Richard Ellis looks to the very birth of the universe but he stands in that same tradition so I'm sure George Darwin would much approve of tonight's speaker so my very warmly welcome Richard Ellis to speak on the development of galaxies [Applause] thank you very much for that kind introduction good evening everybody I'm going to talk about time travel it's a ancient dream I think that we might be able to travel back in time everybody has their own personal adventure maybe you'd like to go and interview William Shakespeare I'd like to go back and see the pyramids being constructed in real time rather than have to speculate how those magnificent structures were made astronomers are unique as scientists in being able to travel back in time when we look at the Sun we see the Sun as it was just over eight minutes ago that's the light travel time from the Sun to the earth when we look at the nearest star we're looking back to see that star as it was four years ago that's the light travel time from the nearest star to the solar system but the situation changes dramatically when we use a very big and powerful telescope this is the deepest image we currently have from the Hubble Space Telescope it's called the Ultra Deep Field it represents an area about the tenth of the diameter of the full moon and it represents a collected exposure of over a week of solid observing time with the Hubble Space Telescope there are about 2,000 galaxies in this very very small field of view and the ones in colored in in the squares here represent some of the most distant objects that we currently know we're seeing these galaxies not as they were thousands of years ago or even millions of years ago but thirteen and a half billion years ago now the solar system is about 4.6 billion years old the universe itself we believe is 13.8 billion years old so we're looking back about 97% of the way back to the beginning so encapsulated in this image is a time tunnel a tunnel that enables us to attempt to piece together the evolutionary history of the universe a very very large fraction of its total age and so in thinking about development my task has has two rather different themes both involving the word development one is the obvious challenge of piecing together the development of galaxies from their birth to the wonderful magnificent structures that we see around us in the universe today so that's development of galaxies the other is the development of the subject and as you'll see it progress has been very dramatic in the last 10 to 15 years through the development of technologies and clever ideas that have enabled us to advance the subject empirically and the challenge will be to piece this together into a coherent picture of the evolution of the universe and also of course our own place within it so where better to start than our own galaxy so the Milky Way is our own galaxy the Sun is one of a hundred billion stars or so sitting in the Milky Way and the first person in recorded history to get a grasp of the significance of the Milky Way was Thomas Wright of Durham and in 1750 he published this original theory of the universe where he successfully up to a point realized that the band of light that we see across the sky is in fact myriads of stars one the Sun being within that system and of course when you look along this band of stars you see a much larger proportion of stars than if you look at right angles to that band he as so often with philosophers he was a landscape architect he didn't of course have any training as an astronomer but as often with philosophers he embellished his ideas and if he'd have stopped at this particular point perhaps he might have been more famous than he actually is he then went on and said well maybe it's not a plane maybe it's a spherical shell and and then he got very excited and he said at the center of this spherical she´ll is a Supreme Being and so at this point you know people started to lose interest in Thomas right but the idea is very clearly there and you can see this in this very nice illustration somebody who's much closer to a modern astronomer we're really one can celebrate his achievements in the context of galaxies is William Herschel so William Herschel built his own telescopes many of them this is the 12th so called 20-foot telescope it's actually the length of the tube the mirror itself was about eighteen and a half inches across amazingly this telescope operated pretty close to the runway of terminal 5 and yet he made significant discoveries and he catalogued a large number of net what he called nebulae across the sky and in 1817 89 he realized and put forward the idea largely a conjecture I think that some of these nebulae might be systems like the Milky Way but beyond the confines of the Milky Way in other words external Milky Way's and you can read this here he says they may also be called milky ways by way of distinction the confusion was that some of these nebulae were inside the Milky Way but a large fraction of them it turned out were outside so in some sense William Herschel was the first person to conceive of the idea of external systems from his own observations so we come to the 20th century and Edwin Hubble whose name of course graces the hubble space telescope demonstrated Caracara categorically that galaxies such as this one the Andromeda spiral lies completely outside the Milky Way so how did he do this he measured the period of pulsating stars so here's his photograph from 1923 and he found a variable star whose period in days you can see if you probably can't see this but this is 10 day this interval here so this is about three weeks and you can see these stars are varying in brightness and that's because they're stable pulsator z-- such stars are known in the Milky Way and the luminosity of these stars correlates very precisely with their period if you know the period clearly you can see their periodic then you know the luminosity that's the true intrinsic luminosity of the star obviously you know how bright the star is on the photograph so hence you can get the distance and he demonstrated that this wonderful galaxy which is the nearest galaxy comparable in size to the Milky Way lies actually far beyond the confines of the Milky Way so we now see this rich diversity of galaxies many of whose distances have been determined very precisely from these and other methods so we see spiral galaxies like this beautiful example here the Milky Way is a spiral galaxy also very similar to this galaxy you can see it has a a central nucleus lots of blue young stars and spiral structure dust lanes these little black stripes running along here contrast that with this elliptical galaxy whether the stars are very red and old no young young stars no spiral structure very simple structure a purely of stars and then as always there are some galaxies that don't fit into the classification and these are irregular galaxies and I'll say a little bit more about those later now the first thing one might want to do in thinking about the the physical significance of these different types of galaxies is to understand their three-dimensional structure and at this point I'm reminded of an event at the Royal Observatory in Edinburgh where I think they were having an opening a public public evening where the public could come in and see what was happening at the observatory and the astronomist Ronna mer took two pictures like this to a graphics artist and said he wanted to a three-dimensional model of these two galaxies made out of plasticine so that he could you know have it on the opening of the public visits to the Royal Observatory and the graphics artists took these photographs and thought about them for a moment and then about an hour later came back to the astronomer and said do you have a photograph of these objects from a different angle so of course you know one of the challenges is how do we determine the true form of these kind of systems well I suppose one could look statistically over the sky but it turns out we learn much more from the dynamics of the stars and gas in these galaxies so this in this leads me to spectroscopy which is a major theme of tonight's talk when we get a spectrum of a galaxy like this particular spiral here we see strong emission lines from gas hot gas heated by the young stars in that galaxy this line is a hydrogen line this line is a nitrogen line and the wavelength of this spectrum line through the Doppler effect which I'm sure most of you are familiar with is giving us the velocity of the gas in that galaxy so the slit of the spectrograph was placed oh right along this axis here so each point here with respect respectively reflects the motion of the gas at that particular point and you can see it's not a constant it's got a sort of s-shaped curve here and the idea is that the center of the galaxy with respect to the center of the galaxy one side is receding and the other side is coming towards us and so it's that the galaxy is a disc that is rotating and one can plot one can measure the velocity of the gas as a function of the position away from the center of the galaxy and here are some we call this the rotation curve of a galaxy and you can see the galaxies are spinning with a velocity of about 250 to 300 kilometres per second our own Milky Way is shown here actually it's rather hard to measure the rotation over the Milky Way because of course we're sitting within it one would have to have the distances of any object much better to measure an external object but to the extent that we can measure the rotation of the Milky Way it's consistent these galaxies are therefore highly correlated their velocities are systemic and these are what we call disc galaxies and they rotate about once every 200 million years or so now when I was a postdoc at Durham one of the surprising results was that the elliptical galaxies are quite different now as the word suggests elliptical galaxies not all of them around some are elliptical in form and one might have imagined that just as the Sun is slightly flattened because of its rotation in other words it bulges at the equator as as does the earth one might have imagined that these elliptical galaxies were wrote were rotating in order to explain their elliptical shape it turns out that that they're not rotating they're hardly rotating at all so this is an elliptical galaxy and this rather curious looking image is a map made with an instrument actually developed at Oxford that measures the velocity of each point of the stars in this image and blue would be coming towards as red would be coming away from us and you can see it's just basically noise there's no systematic it's not as if one side of this galaxy is moving away from us and the other is moving towards us if the galaxy was rotating in order to explain its shape then as one went to the more flattened ellipticals they would be rotating faster and that's clearly not the case so the explanation of the shape of these galaxies is really quite remarkable this galaxy is made up of millions of stars who each have their own independent orbit within that gal see randomly and the shape of the galaxy is the envelope of all of those orbits so there couldn't be a bigger difference between a spiral galaxy in an elliptical galaxy they have very different velocities of the stars and gas within them and and that is a very important distinction so I told you it's an adventure in looking back in time and I'm going to have to introduce the word redshift and I will explain this so astronomers of course when one look when one looks deep in the universe you're looking back in time as I mentioned but you're looking back if we can look back so far that over the time travel from say a distant galaxy to the earth the universe itself has evolved so one is able not just to look to great distances and back in time but the expansion of the universe has changed the light that was that left that galaxy so you probably know the universe is expanding it's very dangerous to think of the expansion of the universe as galaxies acting as projectiles in pre-existing space so often I'm asked you know where where in the sky is was the Big Bang so the universe is not expanding other galaxies are not expanding in pre-existing space from a point in the sky space itself is expanding you can think of the galaxies pretty well as being nailed to the spot and it's the stretching of space predicted by general relativity that explains the expansion of the universe so concentrate on this particular galaxy here it is sending a light ray to this galaxy here and the light ray is blue but the distance between these two galaxies is so large that the light ray is going to take quite a while to get there and while it travels there space has been stretched and now you go to the top plot and the universe is evolved so when the light ray finally are that that galaxy might be the earth our telescope the light ray has been stretched its wavelength is longer and we call this the red shift the shift in wavelength from the light emitted from the galaxy to that received at the earth now the red shift then is a measure of how much the universe has expanded since the galaxy emitted this light ray here and so we can correlate red shift with what we call look-back times is a very useful concept the look-back time is the time that we are looking back in history so here we are today a redshift of zero is today if we go back to a redshift of one what this means is the universe is doubled in size linearly since the light rain left our galaxy and we're looking back about seven billion years or so if we go to a redshift of two the universe has expanded three times in size and we're looking back to when the universe was about four billion years old or about something like about nine or ten billion years in look-back time so I'll keep referring to look-back time and red shift so that you don't get confused if you prefer to think in look-back time remembering that the universe is 13.8 billion years that's fine if you can grasp the idea of redshift I'll be very pleased so obviously we need to get spectra in order to measure these red shifts and measure how far back in time we're looking we need to time slice the universe in different in different redshift bins and so in order to do that we need to measure this wavelength shift and now I'm taking a picture of a galaxy is one thing but getting a spectrum of a galaxy one has to break the light into its spectrum spectral properties and of course that takes a lot more observing time so for example a very faint galaxy might take half a night of exposure on the largest telescope to clinch its redshift clearly astronomers are competitive individuals we don't get the telescope entirely to ourselves like William Herschel did we have to compete we might get three or four nights a year or six nights something like that on a large telescope so if it's going to take half a night to measure a redshift we're not going to make much progress in getting large statistical samples so the first technical development if you like bearing in mind the theme of development that I want to introduce is what we call multi-object spectrograph ield of view on the sky you saw that picture there were many galaxies within a field of view on the sky the field of view is covered by this brass plate which was placed at the focus of the telescope and holes are drilled in this brass plate at the precise location of 50 galaxies and this rather Heath Robinson looking apparatus takes 50 optical fibres fiber-optic cables and each fiber is placed within one of these holes this is an excellent job for a graduate student and each each fiber has a number and each hole has a number and heaven forbid if you should lose that piece of paper that tells you you know so we began this in the 80s with the anglo-australian telescope and it was a big hit imagine now measuring the spectra of 50 galaxies simultaneously that's a huge step forward in a way it's like having a telescope 50 times more powerful but really we realized that this manual mode you know was not no not really the the endpoint of this development so a few years later we developed an automated way a wrote a robotic system where a robot comes along it's an electromagnet it picks up a fiber say from the periphery here and moves it to the precise position of a galaxy the light comes down from above on this from the sky as one of these little units which has a tiny right angle prism in it which deflects the light into here and then all of these fibers are gathered together and fed into a spectrograph largely as a press PR stunt we we got this you know robot to make a map of Australia to which the response was always what about Tasmania anyway this led us up to a hundred objects and then this culminated in one of I think Britain's biggest achievements in this area which was a much more advanced robot which was able to move 400 and this was called the 2 degree field facility and here it is on the prime focus of the telescope and when I was in Cambridge many of us in Cambridge with our colleagues in Australia we did the survey of a quarter of the million galaxies with this instrument now this robot moves these fibers one by one and so it's still not optimal because it took 10 minutes to position 400 galaxies the way this was dealt with with this instrument was that we had a sister equivalent instrument at the bottom here so while we were exposing with one set of 400 fibers the robot was positioning the next set and then a massive tumbling took place so that the one that had been predetermined positions had been predetermined flipped up to here and then very little observing time was lost well I'm going to bring you up to date we're now building an instrument that will do this for 2,400 galaxies at a time and we're planning with the Japanese 8.2 meter telescope to do a survey of 10 million galaxies and we've broken this this barrier of symbol moving the fibers one by one with a very clever idea that our colleagues at the Jet Propulsion lab came up with so we have the fiber runs through a little unit like this which is about the size of my little finger and viewed from above there are two motors two small piezoelectric as one here and one here and via this eccentrically mounted to motor system if the fiber tip is here you can see we can patrol any area enclosed within this dotted circle so we line them up and then we insert them in here and we build up 2400 of these and they're all moving independently and it only takes 40 seconds to configure 2400 galaxies so this instrument will be ready in 2017 and it will do a 300 night survey of distant galaxies with this technique so this is where we were with the older instruments this is really the culmination of the surveys my colleagues and I did at Durham and what you see here is and this was with the anglo-australian telescope what you see now here is redshift conveniently for those who don't like redshift this is the look-back time in billions of years so this is about half way back to the Big Bang and each point here is a galaxy and I've plotted the luminosity because galaxies don't all have the same luminosity some are feeble and some are luminous and so as you go to fainter surveys it certainly you look deeper in the universe but you also pick up feeble objects that are nearby so I think you're familiar with this if you go out into the street and you look at lights you can't really judge how far away they are it could be a headlight a long way away it could be you know a feeble lamp pretty close by galaxies are very much the same as we probe deeper and measure their distances or redshifts you can see that we uncover feeble objects as well as more distant objects so it's not a very efficient way of probing to the very far edges of the universe just going deeper going to fainter galaxies is not necessarily optimal so one of my colleagues at Caltech Church know Chuck's ty Dell came up with a very clever way of pre-screening which galaxies are truly distant and the idea is that hydrogen the most abundant element in the universe has a very strong absorbing effect at ultraviolet wavelengths so that the spectrum of a galaxy is curtailed out of at a wavelength which is known it's in the ultraviolet and so with the clever use of three filters a red filter a green filter and an ultraviolet filter you can find in advance which galaxies are truly distant so let me explain here's a galaxy that's visible in the red filter visible in the green filter and it's visible in the ultraviolet filter so it's not so distant that there's hydrogen absorption has taken effect here's a galaxy that's visible in the red filter the green filter and it disappears in the ultraviolet filter so what's tidal did was to take huge areas of sky and just find these objects they're called dropouts the idea being that they drop out of view in the shorter wavelength filter and I remember this very well in the 90s it was a breakthrough suddenly we went from you know what had taken me a huge amount of effort with with the telescopes that were available at the time to a redshift of 1 he was able to go out to a redshift of 3 so Hubble Space Telescope was launched in 1990 repaired in 1993 and now that we have the distances to populations of galaxies out to redshifts of 3 in and beyond one can get the first simple view of the evolution of morphology of galaxies in the universe so here are here are some familiar galaxies here is a classical elliptical galaxy nearby and here's a very nice spiral galaxy so the surveys that I did probe to a redshift of one that corresponds to when the universe was just under half its present age five billion years here are some galaxies whose redshifts are known and you can see these two look pretty pretty similar to this elliptical galaxy here's two here are two objects that have nuclei there's a there's a sort of spiral structure and maybe it's not so beautifully delineated there looks maybe a little immature but one could argue that these objects are already beginning to form spiral structure and then here are two irregular galaxies I showed you that there are regular galaxies today it turns out there are many more irregular galaxies at this time than in the present universe but if you go to the highest redshifts redshifts of three when the universe was only two to three billion years old the galaxies bear no relation to the galaxies that we see today there are no spirals no obvious ellipticals many of them are multiple as if they're merging and assembling from smaller units let's have a zoom in on these they're physically very small they're ten times smaller than the galaxies we see today like the Milky Way yet they're forming stars prodigiously so the Milky Way is forming stars at the rate of about one Sun one to two suns per year these galaxies are forming stars ten times faster so clearly they're in a very active more might even say adolescent phase and then there are these multiple components what does this mean why are these merging and assembling of a merging systems that are building up to larger systems from smaller units now Hubble of course gave us this wonderful view of the distant universe by virtue of the fact that it's above the Earth's atmosphere so there it is few hundred kilometers up it goes around once just over an hour or so all the time and it's been a phenomenal success and of course one of the reasons why it's been so successful is it is above the Earth's atmosphere and so it's unaffected by the blurring and the twinkling of starlight and galaxies light that we see from the ground I now come to the second technical development and that is a technique that we call adaptive optics and adaptive optics has revolutionized our way of looking at these galaxies with our ground-based telescopes complementing very nicely what we can do with with with Hubble so these are the twin Keck telescopes the 10-meter telescopes on Mauna Kea in Hawaii and what you're seeing here is two lasers being launched into the sky these are sodium lasers 10 watts or so very powerful and they illuminate a layer of sodium atoms high up tens of kilometers up in the Earth's atmosphere sodium gets deposited in the Earth's atmosphere from meteors burning up and so when the laser shines on these sodium atoms it of course the laser beam is very very sharp it creates an artificial star and that artificial star is then monitored as it's light comes through the atmosphere it's a very bright artificial star and we can actually monitor weather with an instrument we call the wavefront sensor the corrugations in the incoming light as it comes through the atmosphere and reaches our telescope and this signal this distortion in the incoming beam is used in a control system to adjust a deformable mirror so these are very expensive pieces of equipment a mirror reflecting mirror which has many many individual elements each of which can be activated according to the signal that's received from this wavefront sensor the biggest deformable mirrors now have 3000 components and we have one at the Palomar Observatory the one at Keck in is is very powerful and with this adaptive mirror we can then correct the incoming beam from our celestial target say the faint galaxy in sync with the signal that we see from the laser guide star so we create images and spectra that are better than those from the Hubble Space Telescope you look somewhat in disbelief we couldn't possibly outpace the Hubble Space Telescope this is a picture of two pictures of Neptune taken with the Keck telescope under normal you know pretty good conditions and you can see there probably some some features here this is the same on the same nights with the adaptive optics at the Keck telescope switched on and this these are infrared images now Neptune has a ring you can see it's very very sharp just like Saturn these are clouds of methane in the atmosphere of Neptune and you can see that these are taken on different nights you can see the weather developing on Neptune not a hope of doing that without adaptive optics and these images are sharper than those that one could get from the Hubble Space Telescope this is the center of our galaxy the center of the Milky Way is a very very rich area where there are lots of stars this is in the southern sky and not easy to see with the Keck telescope but in June and July it can be seen and studied and if this is this is what we see without adaptive optics this is what we see with adaptive optics and of course one can measure the positions of these stars in the center of the galaxy very very accurately one wouldn't be able to do that without adaptive optics and Andrea Gertz who's a professor the UC Los Angeles has during her career has measured very carefully the motions of all of these stars and their orbits she's followed their orbits and demonstrated that there is a massive black hole in the center of the galaxy so what have I done with adaptive optics so what we've been looking at is do and galaxies to see whether there's the beginning of rotation so here's a very distant object and you can see again one side of the galaxy is moving away from us and the other side is coming towards us and this is a very nice rotation curve now the velocities are not as high if you remember the Milky Way was rotating at about 220 kilometers per second this galaxy is rotating about 45 kilometers per second but this is at a redshift of 3 when the universe was only 2 2 billion years old now there is one big difference which gives us the confidence that this is an object that will become a spiral galaxy but it's not yet completely settled down and that's that there's a lot of motion that is random what we would call the turbulent motion of the gas so it's as if the disc is of this galaxy is somewhat still thick and settling down it will eventually settle down and become a tightly rotating system but it is still a very very small system and so it still has to grow likewise we can track the history of the elliptical galaxies and they're growing too so this montage from Hubble where we have the redshifts of all these objects shows what I've done here is that each redshift I've collected a set of galaxies and I've made the images the same physical size in real units so you can see as we come down to the present day the galaxies are just they're very similar actually morphologically but they're just growing in size so the evolutionary history of spirals and ellipticals seems relatively straightforward then spirals are slowly settling down into disks that are rotating the ellipticals are growing in size but maintaining their morphological morphological forms now there is a danger in this kind of simplistic view that galaxies may may somehow migrate from one morphology to the other and that's always a challenge in making a general picture so the question that arises now is what is the physical mechanism by which these galaxies grow both the ellipticals and the spirals are very small at early times but by the present day they're very much larger so there are three ways in which or three physical method mechanisms that are important in the growth of galaxies one is the gravitational attraction of gas onto galaxies now galaxies are formed of gas clouds though the universe contains a lot of gas outside galaxies so in between galaxies there's material we call it the intergalactic gas it's very tenuous a very low density but the universe is a very big place so there's a lot of gas out there and of course it's gravitationally attracted so that gas can fall in and it will be pristine by which I mean it hasn't been polluted by star star formation so it's really largely hydrogen and helium the atoms that formed in in the Big Bang galaxies can merge we saw in those Hubble pictures that galaxies are close together so a galaxy can grow by meeting another galaxy and merging and building a bigger system so theorists calculated many years ago that if these two methods were the only way in which galaxies grow they would grow much faster than we observe so there must be some regulating mechanism that slows this process down so that it's compatible with observations and galaxies can be pretty energetic places so stars when they die they explode briefly in a huge release of energy that creates velocities for the gas it can it can even send the gas out of the galaxies black holes in the center of galaxies just like the one I showed you that we believe is at the center of the Milky Way when they're active they can expel gas and heat it up and so the balance between these two processes particularly the inflowing gasps that's pristine and the outflowing gas which is of course processed because it's expelled from stars which are nuclear factories that are converting hydrogen and helium into heavier element gets us into the very interesting topic of the chemistry and the evolving chemistry of galaxies now we see today that the chemistry of a galaxy varies with position so if we look at a big spiral galaxy for instance the oxygen abundance of the gas is higher in the center than outside whereas if the galaxy is merging that gradient that chemical gradient across the galaxy has been is is pretty pretty small and likewise we expect that if there are big outflows of hot gas then this will erase these chemical gradients so the key measurement really that will determine these competition between these outflowing feedback processes and these in infalling cold gas is to measure these chemical gradients now that's a pretty big challenge so I come to or lesson there's a movie must have the movie so this is a a movie simulation by one of my colleagues at Caltech of two galaxies you're looking at the gas and these two galaxies are spirals they have disks and the first thing you see when they come close to each other is that the disk is very fragile the disk gets disrupted very easily the gas can get expelled into new orbits it can be randomized and of course it can be heated up as well and then but there but at the Centers of these galaxies there are two small black holes and these galaxies merge and create a much larger black hole and that black hole has a huge amount of energy and it can expel the feedback from that black hole can expel the gas out of that galaxy entirely so clearly this process of out flowing gas is very very important in understanding the Assembly history of these objects and how they get bigger with time so the third development is gravitational lensing it's is a very important tool now for astronomy no prizes guessing who this is but of course he predicted that light would be bent by massive objects and this was verified by another pluming professor Arthur Eddington here at Cambridge at an eclipse in 1919 we're coming up to the hundredth anniversary of this famous Eclipse where he took photographs that showed that at the time of an eclipse star light is deflected gravitationally by the gravitational field of the Sun and arguably this really catapulted Einstein for fame and this gravitational lensing technique a few years ago my wife gave me a an stein calendar you know it's one where you know every month Einstein is doing something different you know it was Einstein against the blackboard and then you know Einstein on a bicycle and by the time we got to April I realized mind Stein only had one suit never seen him in anything other than this one suit so here's here's the size of a galaxy at a high redshift and you've already seen adaptive optics so we resolved the galaxies this is the size of the galaxy here's how well we do with adaptive optics gravitational lensing is like a natural telescope it stretches the galaxies on the sky it magnifies it think of it as a magnifying glass a natural magnifying glass so we get an additional boost in the magnifying power of our telescope it can be as much as a factor of 10 or so so my students and I have been working quite hard to look at these gravitationally lensed objects to measure the chemical gradients and sure enough we've succeeded in measuring these gradients so here is one of these distorted images here it is in hydrogen here it is in oxygen here it is in nitrogen and these gradients are very very much steeper than the gradients that we see in nearby systems so we're slowly we've done about fifteen objects now we're slowly building up a picture of how these chemical gradients are growing with time it's very challenging work but to the extent that we've made progress we're seeing broadly what the what our theoretical colleagues predict the theorists are always ahead of the observers is extraordinarily depressing but you know we just have to live with it if we verify their theory that of course they're very pleased if we disprove it they don't believe the observations so anyway here's here's the growth that was predicted and you can see to the extent that we have data we we verify it for the mergers the gradients are raised and indeed that's more or less what we see so time is running on I want to get to the last part of the talk which is the very birth of galaxies and I think this is a very exciting area at the moment here's a artist's impression of the history of the universe starting with the Big Bang and about three hundred and fifty thousand years after the Big Bang the hydrogen the universe expands and cools the hydrogen atom forms for the first time the universe is dark there are no stars or galaxies there's dark matter which I haven't had time to talk about but the dark matter we think is not the stuff that makes up you and me but is a different particle that has already detached from the expansion of the universe and it has mass and so it can cluster and act as little nuggets that the hydrogen atoms now fall into and eventually these hydrogen clouds collapse they get hot at the center they ignite nuclear fusion and so we see what we call cosmic dawn the very first moment of star light in the universe now these stars have only hydrogen and he they're very very hot and they emit copious amounts of ultraviolet light which breaks apart the hydrogen back into a proton and electron the energy from these stars is so intense it is the hydrogen again we call this realization and so this is shown here these ionized bubbles eventually overlap and the universe becomes completely ionized which we've known since the 1960's that the height of the universe is ionized in deep space today so I like this slide very much it's produced by Professor avi Loeb he's at a very minor Community College on the East Coast you've probably haven't heard of it but there's a simulation of this process and I like this very much so what you're seeing is the dark ages in black where the hydrogen is is completely neutral and these blue regions are the ionized bubbles and this is a cube where the expansion of the universe has been taken out so that you know it's more easy to see and this cube you'll see as these ionized regions get larger they eventually connect like Swiss cheese and so one starts to see the entire network connecting and eventually the universe is completely ionized the red regions represent the boundaries between the neutral and the ionized regions so there's a rather slow movie but this is 200 million years so ah and it's produced by Tom Abel and his colleagues at Stanford so can we see this moment wouldn't it be amazing to go back and witness directly cosmic dawn the switching on of star light in the universe so a few years ago my students and I thought well this is something that we should push Keck a big telescope like Keck of course isn't there's no point doing small projects on it we should do something very ambitious so we started using the Hubble images to target extraordinarily faint galaxies and doing two night exposures and we got to a redshift of six which is when the universe about a billion years old about 7% and what we see is this glowing line of hydrogen so what you're seeing here in black is an ultraviolet line of hydrogen called Lyman alpha and it's been red shifted by this these numbers redshift of 6 into the optical and far red region of the spectrum these annoying stripes are hydroxyl lines in the Earth's atmosphere which of course one has to live with now this hydrogen line is very very common it's the most common line in hydrogen in a galaxy and the reason is that if the galaxy is forming stars the Stars heat up the hydrogen gas and it glows in this line so for atomic physicists it's the it's the N equals to 2 N equals 1 transition in hydrogen is the most common line but it's in normally in the ultraviolet unfortunately or perhaps fortunately this line is very fragile if this line if this photon at this wavelength encounters a neutral hydrogen atom it gets scattered so if you're sitting in the dark ages this hydrogen line will not travel very far if you're sitting in one of those ionized blue bubbles this line will escape and by the time it reaches the edge of the ionized bubble it's it's no longer in resonance with the hydrogen and so it escapes so this is a complex idea so I have a little analogy for you it's very much a Los Angeles analogy I'm afraid basically you're sitting on a bridge looking down the freeway and you're looking back in time every car is a galaxy and every headlight is this glowing hydrogen line and as you go into the dark ages the cars are there but the headlights basically a scatter the light from the headlights is being scattered by the neutral gas which is a fog so it's a very simple test we should see the visibility of this line going down as we enter the dark ages and sure enough that's essentially what we've been able to see so here we were at a redshift of 6 1/2 the galaxies show this hydrogen by the time we get to a redshift of eight non of them do so we're pretty sure that we've nailed when the Dark Ages ended and was pretty well about eight hundred million years after the Big Bang so how much further back can we look so this back to this very deep Hubble image here are the most distant objects incredibly faint they're at redshifts up to 12 or so so over the last two years now various groups have charted the number of these galaxies as we go back to these high redshift sand you can see it's more or less continually declining and so we've we've we've pushed back to when the universe was 350 million years old and they're still shining galaxies out there so sadly we're not quite there we've not yet quite reached cosmic dawn but the future I think is is is is pretty exciting and I'm talking now only about two to three years initially and then finally with these giant telescopes so this year saw a completion of an amazing instrument in Chile as a global instrument involves Europe United States and Japan called Alma the Atacama Large millimeter array it is a network of telescopes each one is a pretty significant telescope it's an interferometer that gives us exquisite resolution so it gives us Hubble resolution at millimetre wavelengths and that millimeter wavelengths will allow us to trace the chemistry of the gas in these distant galaxies so that's a very immediate an exciting opportunity in 2018 we will launch the James Webb Space Telescope which is the successor to Hubble and one of the goals of the James Webb Space Telescope is to search for these earlier periods it has a spectrograph on it called NIRSPEC it's already being built and delivered that will measure the composition of these early galaxies here's a galaxy of the kind that we're just barely detecting with Hubble and we will be able to measure the oxygen lines in these galaxies so the ultimate test of a first generation galaxy would be of course no heavy elements so this is I think a very exciting opportunity - and then finally Mary mentioned the thirty meter telescope I moved to California largely to get involved in this it's turned out to be much bigger adventure than I ever imagined initially it was going to be a partnership between Caltech and the University of California then we co-opted Canada and Japan and now China and India and I'll leave it to your imagination how interesting it's been to bring together those very diverse communities and agree who builds what and you know how much observing time everybody guess but we have achieved that we have a partnership that's now cemented we had our groundbreaking ceremony last October so this is a telescope that's three times the diameter of the Keck telescope it will be on Maui Kea right next to the Keck telescopes the Europeans they had to have a bigger one you know when I was in Cambridge Andy Fabian and I would always grumble about how everything had to be bigger in America but now I've seen it from the other side of the Atlantic the Europeans had to build a bigger telescope 39 meters they originally had a hundred meter telescope this one's called the extremely large telescope their original design was a hundred meters that overwhelmingly large telescope but seriously is going to be fabulous having these two telescopes there in different hemispheres and I'm optimistic there will be partnerships between them one thing they have in common is the mirrors are segmented and made of many small units and of course that's been pioneered with the cap telescope so TMT will have 492 segments so that's going to be quite a quite an exciting development so thank you very much for listening in answer to the question of whether this is all worth it one goes back to Edwin or not a not a very popular man with his colleagues he went back he was at Oxford he was a Rhodes Scholar he went back to California and they really disliked his affected Oxford accent but he was a tremendous promoter of science and he gave a series of lectures at Yale University in the 1930s which are written up in a in a book called the realm of the nebulae which actually has just been reprinted and there's this lovely quote in that we search for distant landmarks the search will continue the urges older than history thank you very much [Applause] [Applause] [Applause] so thank you very much indeed the kicked los Galacticos the Milky Way has tantalized people since the very beginning of human search for understanding and perhaps like some of you I've been fortunate enough to spend time in the remote parts of the southern hemisphere you go out in a dark night and look up and you don't see arctos or as we might say the great bear of a plough but you see Orion the Pleiades and the brilliance of the Milky Way and the clouds of Magellan and the challenge to comprehend as you gaze is just overwhelming so Richard thank you very much for a marvelous exposition of our continuing quest to see further and further back and Galileo's Academy is thought to be farsighted but could they have ever imagined how farsighted their heirs would become I think not and we shouldn't either forget that the wider impact astronomy produces wonderful images and is amazing but it also helps shape Society some Paul quotes phenomena by kuratas the great astronomical texts of that time as being a formative insight and later Galileo's vision similarly transformed society so I just wonder what wider changes might ensue as we come closer towards understanding the birth of the universe so thank you very much indeed [Applause] you you

Channel: Darwin College Lecture Series

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Rating: 4.8834953 out of 5

Keywords: Darwin College Lecture Series, Darwin College, University of Cambridge, Development, galaxy, galaxies, luminous stars, space-based telescopes, evolving universe, astrophysics, California Institute of Technology, Richard Ellis, Mauna Kea

Id: AuQCFZIm2Z4

Length: 59min 51sec (3591 seconds)

Published: Sat Feb 22 2020