The Violent Universe - Professor Ian Morison

the violent universe you could have called this the biggest bangs in the universe Plateau such a nice title really so I'm going to talk however about what are the largest bangs in the universe there are two types the major part of the talk I think will be about what are called gamma-ray bursts and the last third perhaps I'll talk about what perhaps was the biggest bang of all the Big Bang at the origin of our universe which was an explosion of a very different and unique type so we've got really two things but they're combined by the fact that there were some pretty big or are some pretty big bangs so to start with gamma-ray bursts and it's an interesting story the discovery of what we call gamma-ray bursts or GRBs for short basically came out of the Cold War in 1963 the USA USSR and the UK signed a nuclear test ban treaty now the Americans weren't at all sure that the Russians would abide by it now they're obviously two things you can do you can try and explode in your clear bomb underground and I can promise you the whole the world was covered with incredibly sensitive seismometers so the Americans could detect any underground explosions but obviously the Russians knew that and it was thought that they might actually try and explode nuclear bombs in space in the hope they wouldn't be detected so in order to prevent that happening the Americans produced a series of what are called Veiler or what were called Veiler satellites veiler means Watchers and they were put up there they had gamma ray detectors upon them and the objective was to detect if there was a nuclear explosion in space a very characteristic signature we might call it where you get in fact a double burst of gamma rays when the nuclear bomb is exploded so these were sitting up in space from about 1963 onwards in 1967 although the data was actually being analyzed by hand it was Nana lye until a couple of years later they discovered a very odd burst that had none of the right characteristics of having come from a nuclear explosion you can see there was an initial very rapid spike and a dip then a rather more gentle spike and then a long gradual tail off and they'd never seen anything like this before it was obviously nothing to do with a nuclear explosion and this is in fact what the team leader of the vaillar project said one thing that was immediately apparent was this was not the result of a clandestine nuclear test well they put more valus satellites up each little series being better than the previous ones and quite a number of events were detected and initially these were classified in fact the vaillar project wasn't actually secret the Americans had told the Russians that they'd done this but it was sort of least not terribly out in the open but finally in 1973 the results were Declassified and clarabel published the first results 16 confirmed bursts in the journal Nature which as you probably know is the UK Journal probably one of the two preeminent science journals in the world it was called observations of gara gamma site gamma-ray bursts of cosmic origin I couldn't find a picture of the appropriate nature journal on the web but this is one I thought would do is actually from 1869 but anyway it's a wonderful journal it's I've had a few papers published in Nature and it is very very vey pleasing when that happens just a little aside on the 22nd of September 1979 Veiler did detect a flash that looked as though it might have been nuclear test it took place over the centre here well they call it the mid-atlantic flash you can argue whether it's Atlantic or the Indian Ocean but it was here that has been very largely classified not very much has come out into the open about that but from what I read and I've done quoted reading that it looks as though it actually might well have been nuclear test which was initiated by South Africa with possible assistance from Israel there are people who say that they are sure that was the case so it may be the vaillar craft did actually achieve one of its prime objectives or its main objective but the real thing about vaillar was it discovered these cosmic these gamma-ray bursts well having learnt about these things you want to find out more so they designed and built the Compton gamma-ray Observatory these things take quite a while to do it didn't actually get launched till 1991 but over nine years had observed over 3,000 gamma-ray births these short rapid very bright bursts of gamma rays it had on it a thing called Batsy the bursts in transit source experiment and essentially there were eight of these little detectors one in each corner so it could look around the whole sky and this is a very significant image it shows you all of the Batsy gamma ray bursts 2704 of four of them basically plotted on an all-sky map with in fact our Milky Way running across the center that will be the center of the Milky Way possibly there's a slight gap there because I think me very hard to see through the middle of the Milky Way but the important thing about that is that is a pretty uniform distribution across the whole sky compare that with this picture which is a distribution of what are called pulsars more a bit about those later on and these are the remnants of stars in our own Milky Way as a result you will expect the majority of them to lie along the plane of the Milky Way because that's where the stars are and that's exactly what you can see here you do see them all around the sky as well but not nearly so many so if you see something like that you say well it's to do with the Milky Way if you see something like this you say no it's nothing to do with the milky way at all these things must be at quite great distances from us in the space beyond our little local universe so by this time it was known that CR bees had an origin well beyond our galaxy as you've just seen there was no bias towards the plane of Milky Way also whenever they looked at where they thought the bursts might have come from which wasn't too easy in the early days they couldn't see anything and that rather implied that these objects were a very long way away so that was a good start but what you really wanted to be able to do was to locate very precisely where this gamma ray burst came from and the next satellite called Beppo Sachs which was an Italian and Dutch satellite played a very significant role in our understanding of these wonderful objects because within seconds of the observation of a gamma-ray burst by its detectors it could actually orient itself and take further imaging to look at what is called the afterglow following the brief few seconds a bit more gamma-ray bursts that tends to be an afterglow in the optical the radio the x-ray and so on so if you can look quick enough you can see that and if your instrument has got much higher resolution then you can actually find out where it is so that's the key thing you want to do and it made two absolutely key observations GRB 9 702 28 which probably tells you it was the 28th of February in 1997 and the other one was the 8th of May 1997 and these were absolutely fundamental to our understanding of what these things actually are not all that long ago really well the first one as I said was detected in February 9 97 and within a few minutes Beppo Sachs had got its cameras onto it and Wow and the position to a precision of about three arc minutes that's not that good but at least it's good enough to allow other telescopes to have a look within the field of view that a typical large telescope has got that actually shows you their image in effect and you can see that this is two art minutes here so the size of that is about three art minutes the fact that says plus means it's in the northern part of the sky and five hours just tells you how far around the sky it is so that's a very very key observation that position was told to the people at the UK's William Herschel telescope they keep on saying they're going to close it down but I think it's still there it's a lovely telescope my boss professor Francis Graham Smith had a lot to do with it some construction and the site is actually at La Palmer on the island of La Palma in in the Canaries they were able to observe that position within 20 hours and they were able to see the afterglow the optical afterglow of the gamma-ray burst so they could refine its position and that meant that the Hubble Space Telescope could then once the afterglow had gone in fairly last a few days could actually look to try and see what was there where the gamma-ray bursts had come from and this is in fact the Hubble image that was produced shortly afterwards that was on September the 16th this is the little bit of the sky you want to look at it's around here that's that bit and that's been expanded so just this bit here is expanded to this bit so that's that this is the galaxy where the gamma-ray bursts originated from it's called a progenitor galaxy and that little dot basically is the remnant of the afterglow of the actual GRB so this was the very first that the very very precise position of a GRB had been found and at least in the first instance it showed it was in a very very faint galaxy which sort of implies it's a very very long way away now they weren't able to get a spectra which lets you find the distance for some time when they finally did they discovered that was the spectrum they discovered that this object was at a distance of 8.1 billion light-years now our universe is about 13.7 billion light years old so can you see you're looking back in time over halfway so this is a very very distant object the next of those pair of that pair of GR bees was in May that year that was detected by Beppo Sachs and the William Herschel telescope here was able to have a look and ajit at optical wavelengths so they got the precise position really quite quickly and this is the Hale telescope the lovely five meter the 200 inch telescope we always used to call it in the days of yore at Mount Palomar a lovely telescope and here you can actually see the OP - laughter glow actually going up this has made the night it peaked on May the 10th and then died away again so you get this typical sort of rise and gentle drop in the brightness at these other wavelengths not gamma rays the gamma-ray burst is very short but then you get a rise in the radio the optical the x-ray ultraviolet which you can then perhaps see and this time in fact a very large array of telescopes in America the Americans are not terribly modest about what they call it we have sown we called a very small array which is on Tenerife II but compared to this which is 36 kilometers across our array on Tenerife is only a few meters so perhaps we're not being modest or otherwise anyway it was able to show that the afterglow as seen in the radio was incredibly small in angular I really point like and in fact that shows you in fact the brightness seen on the 10th so the 9th of May and that had dropped quite significantly 14th of May this was the spectrum and that was actually found quite quickly and that had a redshift of nought point 8 and that tells you that the galaxy is at a distance of 6 billion light years at the time that was the most distant GRB the nuoc was a while before they found the redshift of the other one so these things were a very very long way away the fact that we see them implies they must emit a very large amount of energy well the next spacecraft to come along was called Swift and that's still there and this is a multi wavelength space space observatory which means it's got x-ray ultraviolet and optical telescopes as well so the idea is that it actually detects in the gamma rays the approximate position of one of these bursts it then sloughs itself around so that it's optical x-ray and other telescopes can look at that direction at that position I can image it in far higher at far high resolution so there's a Swift spacecraft all the bits that matter are up the frontier these are the cellar panels of course that's looking down on these are artists impressions but the things that matter that is the actual gamma ray detector and then you can see here we have ultraviolet and x-ray telescopes that can be focused or pointed towards the position of the gamma ray burst and that can be done very very quickly so Swift can find the precise position of a gamma ray burst well within seconds or certainly within a minute or so and that's key because by that time or at that time some of the after clothes are really pretty bright so within 10 seconds it's produced an arc minute image and it can point as I said and refine that even better what they then do is that position is radio down to ground and effectively broadcast over the Internet in what's called the gamma-ray burst coordination network so all other telescopes around the world can in principle find out the position of that gamma-ray burst more as within seconds certainly within a minute and this is the basic idea here is a gamma-ray burst this is not to scale as you can imagine here is Swift but there are other spacecraft up there that can detect gamma rays now and it's been detected by Swift it sends down its data to here that actually then sends it back up to these other spacecraft so they can look as well because there's an x-ray spacecraft up there Ulysses and so on but also out to telescopes both radio and optical on the ground so within a minute or so if telescopes can slough quickly you can have a whole host of other telescopes observing the source of the gamma-ray bursts pretty much as it happens and this is one of these high slew rate telescopes not this a very big one that one I think is in Australia but he certainly looks quite pleased with it on the right there one that I know more about is the Liverpool John Moores robotic telescope which is on that Palmer and this is again the same idea here's a gamma-ray burst the gamma rays are picked up by Swift Swift notifies that information by downlink it goes through the internet the local robotic telescope can slough within a minute or two onto that position take an image which is then sent back to Liverpool University to some of my friends there so that's the sort of thing it's now happening every time a gamma-ray burst is detected and they're being happy they're being detected now several times a day basically so that's a rather lovely view of the Liverpool John Moores telescope with the Milky Way above and I always wonder that probably a composite image because that would be jolly hard to take I wouldn't know how to do it but it still looks good doesn't it and this is a lovely telescope they're the two meter telescopes they built a factory which is on the we're all to build these I think they've built for maybe five now two of them are called the falx telescopes do you remember when I talked about the search for Planet X with my friend Samuel here we actually used it robotically to image the most distant object that we know of in the solar system so this is one of the same type of telescope sadly as far as I know they stopped producing them so what's the most distant GRB that we know of well it's actually this one here it's in leo the constellation of Leo it was detected in 1999 don't know I like 2009 so not that long ago and from its spectrum we know that the light was emitted when the universe was just 630 million years old and until a few weeks ago a couple of months ago so that was the most distant object that we knew of in the universe it was imaged with the UK's Germany North telescope it's actually one that's jointly owned and built by the UK and some other people as well I believe in the cuts that we had a couple of years ago we're now in fact stopping using that at the end of this year or end of 2012 I think there's a very nice telescope that's up on the top of Mount akhir and that's a picture of that so that was until recently the most distant object known in the universe I have to tell you that I'm afraid it's been beaten because detailed observations of galaxies in what's called the Hubble Ultra Deep Field this is when the Hubble telescope looks at one spot for days on end integrating the very weak signals it did one in the northern hemisphere we've got involved with the Jodrell Bank with Merlin but the southern hemisphere one we obviously couldn't but that was the Hubble Ultra Deep Field in the south and although you will not see it there there was an object in here which is that little thing you can barely see and that has a spectrum which shows it was actually seen as it was 600 million years after the origin of the universe that's actually a very significant observation because it means as we're going to come to at the very end of this lecture that there was just a period of a few hundred million years before the formation of the first stars and galaxies in our universe just a nice thought in 2008 again not long ago the optical afterglow of a GRB Oh a toh 319 Bibi says it was the second one observed on the 13th of March in 2008 had a visual magnitude for a short while of plus five point eight in principle that is visible on a dark clay transparent night no moon to what I would a few years ago have said was the naked eye but apparently that's politically incorrect so I have to use the word unaided eye um that's true at schools in America and I don't blame them have what they call nanny software that scans everything that people download off the web and it looks for all naughty words and obviously naked is one of these and that meant that schools were not able to download the sites from for example sky and telescope magazine know which is the astronomy map with the best astronomy magazine in the world probably because of course occasion it talked about naked-eye visibility so I don't want that so anyway so the point is had anybody seen that as far as we know nobody did but in principle one could have done the photons that were detected by your retina have left their object 7.5 billion years ago you would have seen more than half way back in time to the origin of Unix a nice thought sadly as far as we know nobody actually was able to do it but it was fun so look we know these things are very very far away so in principle we can detect so we can calculate the amount of energy that they have to produce to make them appear so bright at such a great distance let's do an analogy how can we calculate the energy output of the Sun I would say that probably at least half of you could do that if you had a bit of paper and then enveloped and perhaps a little calculator on your mobile phone you could half you could do it but does anybody think they could do it you'll all say no won't you how on earth could I possibly do that well all you need to know to start with is how much energy falls on one square meter say of the Earth's surface and you'll say well I don't know that below just think about it let's do a thought experiment imagine you were at in the Sahara somewhere and the Sun was directly over your head you'd feel quite hot wouldn't you okay now imagine it the sun's gone is totally dark but above you just in fact if I stand here and don't fall over there's a little light or something first of all imagine it's a hundred watt bulb secondly imagine it's one of those little one kilowatt you know those little radiant lamps you have in bathroom sometimes and thirdly imagine if it's a 10 kilowatt arc light now think don't do anything but think which of those three would be most like sitting there under the Sun overhead hundred watt bulb 1 kilowatt sort of radiant heat lamp 10 kilowatt art like I wish you could all have little but you know these things in they have little buttons and you press which one a B and C decide which it is and don't let anything change your mind hands up those who think it might be a hundred 100 watt bulb one that's obviously in the minority all right hands up those o2 I'm sorry do apologize hands up those at my I think it was about a 1 kilowatt heat ray Lampe actually not all that many quite a few and then is it all the rest think is a 10 kilowatt arc lamp I think you'd be a bit frazzled I mean I was expecting to be honest most of you would say it was like a 1 kilowatt heat lamp because if you stand in one of those in the bathroom you know it feels quite warm but look you're actually between the two of you you're right because the exact number is 1.37 kilowatts so it's not as much as 10 it's a bit more than 1 but look would you agree you could get an estimate at least within a factor of 10 and probably a factor of 2 to 5 do you see that just as a thought experiment it's what we call a guesstimate now the only other thing you need to know is how far it is from the earth to the Sun and that's 93 million miles but we ought to talk about kilometers it's 150 million kilometers if you know what the formula is for the area of the surface of the sphere of that radius you have 4 PI R squared you can calculate how many square meters there are in the shell surrounding the Sun at the distance vert you get the idea all the radiation of the Sun must go through that shell so all you need to know is that area times 1.37 and you've got the answer and in fact 4 PI R squared is the formula we use 1.5 times ten to eleven is 150 million kilometres that's why meters I should say that squared times 4 pi and you multiply that by one point three seven and you get three point eight six times twenty ten to twenty six watts but you get the idea it's not difficult that's exactly what one does with the gamma-ray bursts the amount of energy that's detected is very small but on the other hand the distance is not measured in millions of kilometers it's billions of light years so a is absolutely enormous and basically if you assume that the power is radiated what's called isotropically then in fact it would the energy involved is what you'd have to have if the Sun was suddenly the whole of its mass converted to energy there's nothing that can do that so what we believe is that the energy must be beamed so it's like if you have that a bulb of a torch just by itself powered up to a battery you'd see a little light if it's actually in a torch there's a beam if you look along the beam if you see the beam it looks bright elsewhere you don't see it at all it concentrates the energy so that begins to make sense and the total energy is about having to convert 1 mm the solar mass into energy instantaneously pretty well and that is theoretically possible so that's good it turns out we've seen many thousands of births now there are two types the majority are long period that is they take many seconds maybe 10 20 seconds or so defined as being greater than 2 seconds in length the minority are short period less than 2 seconds or some nice short sharp ones they're 1 or 2 seconds in total length we believe they have two different origins but both result from the evolution of massive stars the long period ones we believe the result of supernova or hypernova the short period ones we believe are the result of neutron stars merging as we shall see so we need to know a little bit about the evolution of stars line I know I talked about this in a lecture a year or so ago called aging stars but I hope you'll let me summarize what we learnt a star forms out of dust and gas which gradually under gravity gets smaller and smaller and smaller if the core reaches a temperature of over about 10 million Kelvin then nuclear fusion starts and it becomes a star and stabilizes it'll time this is our Sun but eventually that fuel runs out it then expands becomes what we call a red giant before it finally explodes and our own Sun does something like this it starts off as a cool bit of mass but it's quite big actually so it's still quite bright it comes down it lives here for a long time then in fact it gets much cooler so it moves over to the this is cooler and redder over here but it gets much brighter because it's very big then it gets all it oscillates a bit blows off the outer parts and the rest is just left behind is what's called a white dwarf as we shall see there's a white dwarf in the constellation of Lyra it's down here this is Vega and there's two stars here and it's just between the two it looks like this the colors you see the red is hydrogen but that lovely turquoise color are the lines of oxygen so in a star once the hydrogen has turned into helium you start building up carbon oxygen nitrogen and other elements and when the star explodes they blow up into its place leaving behind something we call a white dwarf that is held up by what is called electron degeneracy pressure it is a result of quantum mechanics essentially if you try and squeeze electrons too close together they don't like it very much and they will produce a force that can basically oppose gravity and stop the collapse our Sun the core of it will end up eventually as something about the size of the earth that's what happens with sort of smallish stars those about the size of our Sun and certainly smaller and perhaps a bit bigger if you have more massive stars perhaps eight times greater in mass than our Sun they evolved much more quickly they don't live very long as stars perhaps fifteen million years or so they burn helium into carbon and they expand again and become quite enormous they're very cool because they're so big they are very bright perhaps a million times brighter than our Sun they're red supergiant's and there's a lovely example you all I hope seen Orion in the southern sky the last few weeks when it's been clear the upper-left-hand star of Orion is called battle jizz the Americans might say Betelgeuse and here it is a red supergiant it's about the size of the orbit of Jupiter it is really quite enormous so that's a red supergiant and just to give again an idea of scale there's our Sun and Bethel jizz I can't do it but you get the idea it's pretty big they can carry on their nuclear fusion process way beyond smaller stars and they end up with the core made of iron and perhaps nickel they are the most stable nuclei you can't do better than that these stars then often blow off much of their outer envelopes they become rather unstable and the star will come back to called e to Carina that actually blew off its outer layers about a hundred years or so ago and it disappeared for a bit because it was hidden by the dust but now as the dust has expanded you can actually still see the star right in the center come back to that little wall so when these stars come to the end of their lives the core made of iron can no longer produce any energy to support or to oppose gravity it collapses down it tends to rebound once it's got to the bottom the outer parts of the star are falling in or is the inner part and you get sort of one not going in one bit coming out and you get an incredible compression of the gas and you get a thermonuclear explosion of epic proportions that we call a supernova and one thing to know about supernovae in just a few seconds the neutrons flying around build up all the heavier elements than iron so any gold you might have with you basically was produced in a supernova and then these parts are blown off into space was a nice example in constellation of Taurus is up here it looks like that so we do have not very often these fairly epic explosions this is the remnant of a star that was seen to explode in year 1054 another famous one is called Tico's supernova of 1572 but we haven't had one for an awful long time we'd love to have one to look at nearby we're not too close um if the mass of the core is above a limit of 1.4 solar masses then electron degeneracy pressure the thing that supports white dwarfs that had it gravity can actually get overcome that and the thing gets smaller and smaller and smaller until finally it becomes what we call a neutron star a giant nucleus and the something called neutron degeneracy pressure another quantum mechanical effect which prevents any further contraction at this time the thing has a diameter of perhaps 10 to 20 kilometers or radius of 10 to 20 kilometers if something's big rotating slowly and you make it get smaller it spins up so these neutron stars you would expect to be spinning quite quickly well I've talked about this before but very briefly these neutron stars were a theoretical concept and they were discovered in the 1960s by a young lady called Jocelyn Bell who was Tony Hughes students at Cambridge and she helped build a very large radio telescope back she looked a bit like a vineyard but it was a very big telescope much bigger than our Jodrell Bank one and with that she was looking at about 400 feet of chart every day observing a particular characteristic of radio sources and she discovered what she called a little bit of fluff and it turned out that this in fact when they looked at it in detail was not a little bit of fluff it was that a sequence of very short rapid pulses and no one could understand how you could actually get any natural phenomena giving rise to a very accurately spaced sequence of pulses she thought it might be et phony home and she called it lgm1 for little green men one well someone called Tommy gold an American who was working at Cambridge realize what these things were neutron stars very small perhaps 20 kilometers or so across rapidly rotating with an incredibly powerful magnetic field this appears to be usually not along the axis of rotation just like the Earth's field so as the thing rotates the field is going around and this seems to produce beams of light sometimes and radio waves usually which sweep around the sky if one of these beams happens to be pointing towards us at one time of its rotation each time the beam crosses our position in space we see a pulse of energy like that so you can see why you get a very accurately spaced set of pulses those things are very massive they are very very good clocks move that now some years ago astronomers at Jodrell Bank which is where I come from discovered two of these objects co-rotating takes about two point four hours to want to go around the other they're so close you could fit the orbits in the inside of our Sun this is just to try and hypnotize you briefly but that's just an idea of what's going on now Einstein you've all heard of him we've talked about him he says if you have a pair of objects co-rotating then they will emit gravitational waves and that's an idea little ripples of space-time that travel out at the speed of light through the universe but they take energy away from the system that's got to come from somewhere and what happens is these two objects are slowly spiraling in towards each other the rate we have measured at Jodrell Bank is seven millimeters per day it is precisely what Einstein predicts this is the very end of their life the green grid is space-time you can see some ripples going out the two are just about to coalesce into one as they do so you get a gravitational wave tsunami which may be detected before long but did you see that little burst there that's a gamma-ray burst that's one little way of looking at it this is a bit smaller but it's just a slightly more artistic way of doing it here are the two things beginning to coalesce and form one object well we'll see what that gives rise to very shortly we think that the result of that is a black hole which is rotating as you see there and the Jets of gamma rays come off along the rotation axis of the black hole in the center so this is one source we believe in fact the source of short-period gamma rays and this in fact in 2005 is an image of the very first visible counterpart of a short burst GRB as it's called it doesn't have to be the coalescence of two neutron stars oh those are the final moments you can see the two getting closer together they finally come together as one they form a black hole we talked about those not that long ago and you get these two opposing beams of gamma rays initially followed by an arc to glow at other wavelengths and this we believe seen in x-rays by the Chandra satellite is in fact the merger of a black hole with a neutron star so neutron star neutron star black hole neutron star or even a neutron star gradually picks up material by its gravity from the surroundings and finally exceeds the mass that can be supported by neutron degeneracy pressure that will also collapse into a black hole so three basic mechanisms of producing black holes which we believe give rise to the short period gamma-ray bursts so such mergers of neutron stars and the like are thought to be the source of the short period grbs what about the long period ones well we think they come from the final stages of the life of a supernova or hypernova a hypernova is said to come from a star that is actually 200 solar masses so very very massive stars but the two are pretty much the same the word hypernova didn't actually come around until quite recently so the core of a giant star is too massive to be held up by neutron degeneracy pressure and collapses down directly to form a black hole and here is one in the galaxy m74 that's not too far away from us I always like the way you get these big arrows on the sky to help you find things and this is sort of the idea this is a star evolving it finishes up with the core of AI and as I said surrounded by shelves but like an onion magnesium neon silicon carbon oxygen nitrogen helium hydrogen and the center part falls down becomes a black hole and then a rather nice thing happens I show you a movie which i think is really rather good that's just at the start of it the black hole is formed in the center and the two beams of gamma rays are just being emitted from it in opposite in opposing directions what it does it sort of bores a bigger and bigger hole gradually just destroys the star now lovely and right in the center we're going to zoom in now is the black hole you can't actually see the black hole of course surrounded by what's called an accretion disk and it's the material that falls in towards a black hole from the accretion disk that actually does it should I just do that once more I think we can just rather nice if I can actually get there there we go just to see that so this is what we believe is the source of the long period gamma rays and as I said the energy that's given off in quite a short period of time is equivalent to about one two hundredth the total mass content of our Sun these are pretty impressive things and someone went out there with a Cameron took a very nice picture of one in a star cluster that's rather nice piece of graphic art I think so in summary gamma-ray bursts two types the long gamma ray bursts the results that I've just shown you of a massive star whose core is so big when it collapses down nothing will stop it becoming a black hole the second one's a short period bursts when you have two neutron stars say or a black hole a neutron star or whatever they spiral in towards each other that's all down to Einstein he's got an awful lot to blame be blamed for until they finally coalesce and also form a black hole the energy involved there isn't quite as great there's still quite a lot should we be afraid no not really first of all we believe that those very massive stars that form the black holes were more likely to form in the early days of the universe we don't see any nearby which is not too surprising because they're very rare we suspect you'd only have one of these the order of every million years in our Milky Way galaxy and you've seen there beamed and the likelihood of the beam being pointed at us is again quite low so I really think we shouldn't be too worried this is one of the two stars that we think are going to do this in the quote near future but I can't tell you what near is it could be tomorrow it could already have happened and the beams coming towards us at the speed of light but it could well be millions of years in the future that's one of them and I mentioned you to Carina this is in the southern hemisphere but there's an encouraging thing here can you see the axis of the rotation of the star it's that way that's not pointing at us that's important because if that was pointing towards us then at some point in the future it might be a problem in the southern hemisphere what could happen if a gamma-ray burst reached the earth it could destroy the ozone layer it would let much more ultraviolet light reach the ground it could really cause a major problem and some people suspect that one of the mass extinctions about 440 million years ago could have been caused by a nearby gamma-ray burst we think the number of stars that's going to do this is very low but there's nothing to stop two neutron stars coming together they'll be happening at fairly regular intervals but again very rarely so I think we can go home and sleep easy tonight so just for their final 15 minutes let me say something about the Big Bang origin of the universe which you could say was the biggest bang that has ever happened just to set the scene and my final lecture by the way called to infinity and beyond I will try and summarize take you through the last almost a hundred years of cosmology how its developed as a subject and what we suspect it may be happening to it in the future so this is just a little bit where I can spend a bit more time about the Big Bang than I'd be able to in a single lecture Hubble showed the universe was expanding a bit more about that in the next lecture which is called Hubble's heritage a a freedman a Russian derived an infinite set of models using Einstein's general theory of relativity to model an expanding universe as we shall shortly see in all these models the whole universe expands from what is called a singularity zero sized infinite mass and density if you came to my lecture on black holes you know I don't like singularities essentially it's where the physics in this case general tivity breaks down Fred Hoyle called these the big this the Big Bang model these the Big Bang models of the universe and the point and the origin is thus called the Big Bang I'm sure you all know that there are three things I'd like to say because I often get asked questions to these three points where was it and the answer is it was everywhere the whole of the universe was once essentially I'm not going to say at one point as you'll see later on but within a very very small volume of space perhaps a metre across so we were all together or least whatever caused this eventually we were all very close together in the same point everywhere in the universe now was once at the Big Bang secondly where is it expanding into the answer it isn't it did not expand into space it is not expanding into space now the Big Bang created the space into which it's expanding so space was created by the Big Bang it wasn't there before in the currently accepted theories it was also the origin of time as saga Stern has said the universe was created with time not in time I don't actually think that was a quote because I tried to find it but it's just an encapsulation of a somewhat longer thing that he said but essentially that's the essence of what he said and he was in that sense right the universe was created with time not in time time did not exist before the Big Bang okay that was thus those were the standard Big Bang models but it didn't take an awful long time well that's what he did from about 1930 up to about 1970 for people to realize that there was some real problems with this sort of standard Big Bang model one of them which is my own worry is not one that you generally read about I don't like the thought that all the mass and energy of the universe was once in the singularity of infinite density I say as others do it just means the theory of relativity has broken down and you'll see what I think happened or what we think happened shortly there's a second problem Freedman produced essentially an infinite number of models of the BIGBANG universe they all start from the Big Bang at the origin it's a little bit like me throwing the ball up in the air if there's not enough energy of expansion in my case throwing up a ball fast enough gravity wins and the universe is collapsed down again so there's an infinite variety of what are called closed universes where the universe expands to a maximum size and then collapses down to what's called the Big Crunch we don't think this will happen but if it did it would be at least 120 billion years so again don't worry about it now if I kept on throwing up a ball at faster and faster speeds there would come a point where it would just leave the earth it would carry on slowing down with time until eventually it came to a halt infinite time in the future at infinite distance that's just having got what we call this scape velocity here there's what we call the critical universe where that's exactly what happens the universe continues to expand at an ever reducing rate until it comes to a halt at an infant time in the future that's just one case it's the case between what I call the closed universes which will eventually come back and the open ones that just go away and expand a bit faster and what we now know is that we are very very close to this and there's nothing in the laws of physics that says why that should be so that's a slight worry the other things call the horizon problem if there was a Big Bang the universe was once very very hot as the universe has expanded although the temperature would drop it wouldn't drop to absolute zero and way back George Gamow and his students predicted the universe if you put a thermometer in the middle of nowhere would measure about 10 Kelvin 10 degrees above absolute zero Richard Dickey predicted it was about 5 Kelvin the radiation related to that temperature was discovered by Penzias and Wilson who got the Nobel Prize and it's actually a 2.73 degrees what they found though was the temperature in every direction they looked was identical and that's called the horizon problem how can that be look at there's a problem the radiation that reaches me from over there has only traveled 431 has trouble for thirteen point six billion years the age of the universe the radiation that reaches me from over there has traveled the same time but there's no way that any radiation from over there could have got to over there because the universe isn't old enough so how do they know the same temperature here's an analogy I'm on a ship and it's a British ship you see it's got a red inside okay now over the horizon I see the mass of obviously I don't actually see the whole of it but I see this ship and I see it's got a flag well I don't see that to start with but as I'm a strum I climb up to the crow's nest and I have a telescope do you see the telescope yeah and then I can see the flag on that ship while I'm up there I look in the opposite direction and I see another ship and it's got exactly the same flag and I can only just about see that above the horizon can you see that the people on those two ships cannot see each other they're below each other's horizon so how have they got the same flag the obvious thing is they've come from the same place some port somewhere and they belong to the same shipping line or the same area at the same Navy whatever so at one point in the past they were causally connected that's the word we use that they were then a sufficient volume of space that information could travel between them at no more than the speed of light so what we say is that the universe had at one point to be so small that the whole of it was in thermal equilibrium and that can't be the case in the standard Big Bang Theory it was Alan Guth who came up with an idea and I call it an idea not a theory to start with the idea is called inflation that prior to inflation there was a little bit of space tiny probably almost empty but then over a very short period of time and the times I've given in the transcript I'm not going to go through them now detail it expanded by some enormous factor 10 to the 50 10 to the 60 in size and that's a lot of expansion in a short time and we call that inflation we suspect that at the end of the inflation period the universe was somewhere between the size of a golf ball and a metre ball something like that but of all disguise of a meter and then it continued to expand in the way of the standard model now there are two things that result from this first of all if you blow a balloon up by 10 to the power 6 T times can you see what was once possibly a curved surface becomes flat it's got so enormous so it drives inflation would make us live in this basically critical universe where we say space is flat more of that in the last lecture so that's a good thing also prior to inflation everywhere in the universe was causally connected so it could all be at the same temperature so in the revised model the initial infinitesimally small volume of space from which our universe sprang may have started from effectively nothing a little quantum fluctuation had the right properties to allow this period and inflation now this is the key thing which solves my other problem at the end of the inflationary period when the thing was really big there was what they call a phase transition associated with what's called a strong nuclear force don't worry about that but essentially that phase transition created a vast amount of energy energy equals matter that's where everything came from so it wasn't all in a tiny point it was all perhaps once in something about the size of a meter which I can cope with a bit better whether you can lots of them anyway now how can all this lot how can everything in our universe come from nothing and the answer is that the universe in total is nothing the total energy content of our universe is actually zero now the point is all the matter that exists in the universe is what has got what's called gravitational potential energy and you can regard that as being negative look if you have a car a top of the hill and you put it off it rolls down the hill it gathers speed so it gathers kinetic energy and actually a little bit of mass - according to Einstein at the same time it loses gravitational potential energy so the two are sorry can be opposite and it turns out that in the flat universe there's an exactly equal amount of negative gravitational potential energy as there is and everything else so the sum of the two is zero so we're a big sort of excursion from nothing at the end of this time there was what's called a quark-gluon soup a mix of quark and gluons but it was too hot for protons and neutrons to form the things we know about and I just want to quickly say that rather nicely I told you this before Christmas that in November I think it was Alice which is one of the detectors in the Large Hadron Collider basically crashed together beams of lead nuclei and produced a quark gluon soup I'm sure you can all understand that but those are the tracks of the various particles the quarks different types of quarks and the gluons that were produced in this explosion and that's the first time in effect we've created the conditions that happened a billionth of a second after the origin of the universe that's really good there was a slight excess of matter over antimatter we believe that virtually identical amounts of matter and antimatter were created that's what should happen but it looks as though because of something called charge parity violation which you can believe or not but it may well have happened that there was about one extra matter particle for every billion antimatter particles so a billion antimatter a billion one matter particles obviously what does matter and antimatter do you all know about that if you've listened to read one of them those books they annihilate and you get protons and antiprotons annihilating electrons and positrons annihilated all the anti particles disappear just leaving a an awful lot of high energy photons and be relatively small numbers of particles the one and a billion that were left so only matter particles were left we live in a matter universe now finally got cold enough for the quarks to form neutrons and protons it turns out that neutrons are unstable if you had a million of them in ten minutes you'd only be left with 500,000 half of them would go it's called the half-life and they turn into protons electrons and anti neutrinos so the neutrons began to disappear and the only ones that were left with those that were locked up in the nuclei of helium helium three deuterium and lithium so we have far more protons in our universe now than we have neutrons and that was because the neutrons decay the relative amounts in fact of those four elements tell us quite a lot about the early stages of the universe by this time there should have been a lot lot more antimatter particles but because we don't know what they are we don't know how they were formed that's still a very big question mark over the whole of the Big Bang idea how did we get all of the dark matter particles but they were there so now finally we nearly they're the building blocks of our universe existed but the atoms still could not form the photons were very energetic and sure the little electron attached yourself to a proton to form a hydrogen atom very quickly a photon comes along kicks it off into space so essentially the universe was filled with photons electrons and also alpha particles as well the electrons scatter light just the same way that water droplets scatter light in a fog and there's a nice picture showing a fog bank over here and a bit of an analogy would you agree the fog bank is some distance away from us so the light that reaches us from here has taken a longer time to reach us in the light or anything between us where we can see so we're sort of looking back into time a bit to a point where we can look no further and this is exactly the case in our universe as we look further and further back into time we come to the point when there were the free electrons then the universe was opaque it looks a bit like a fog bank 380,000 years after the origin nearly finished as the universe kept expanding the photon energy dropped and then the protons and electrons could form hydrogen the alpha particles and electrons could form helium and so on so we had the building blocks the atoms of matter at that time the temperature was about 3000 Kelvin so the universe was filled with a sort of a yellow orange light that's what you get at about 3000 Kelvin since then the universe is expanded by about a thousand times and the temperature has fallen by the same ratio to about three Kelvin it's actually 2.73 Kelvin that is now that radiation is in the infrared and the and the radio so you have to be a radio astronomer really to see it and this is a map I showing you a year or so ago of the fluctuations of that this is looking back at that fog bank and you see it's not totally smooth it's got structure and that structure is basically caused by the dark matter that's around perhaps six times more of that the normal and they form concentrations little gravitational wells into which the hydrogen and helium could fall and gradually get concentrated and so form a few hundred million years later as we saw the very first stars and galaxies those fluctuations we see are actually quite a good thing to tell us that inflation probably happened it's not a hundred percent right it's pretty good we've learned about dark matter just said that so essentially the hydrogen the helium was able to form the first stars and galaxies some of them are very big became these hypernova and that's the Hubble image of the early days of the universe some of those galaxies there as when we saw just earlier some of the earliest objects to form in our universe and so eventually about 500 million years or so after the Big Bang our universe had sprung into life thank you very much you

Channel: Gresham College

Views: 47,492

Keywords: supernovae, hypernovae, Big Bang, Gamma Ray Burst, Space, Star, Stars, Universe, Galaxy, Stephen Hawking, Science, NASA, Jodrell Bank, Space observation, Space Science, Ian Morison, Gresham College, Gresham, Gresham Professor, Gresham Professor of Astronomy, Professor of Astronomy, lecture, talk, astronomy talk, astronomy lecture, education, free education

Id: MQSIKmoGqDI

Length: 63min 16sec (3796 seconds)

Published: Thu Aug 25 2011