Transcript for:
Extremes of the Universe: Power and Phenomena

sleep and study don't forget to subscribe talking about the extremes of the universe I'm spoiled for Choice one of the extremes of course is the Big Bang which is the origin of space and time that started it all but I'm not going to go and talk about cosmology I'm going to talk about the extremes of power in the universe the most powerful things I'm looking it up nearby Powerhouse the sun in this little movie and and you can see all these eruptions of material above it uh these are solar prominences which are visible the lives of hydrogen Alpha and we're going to go on and look a bit at those things but in a sense what the theme is it's going to be about power in the universe what are the most powerful objects in the universe that we can see and often it's involving magnetism sometimes it's gravity most often gravity and magnetism that is driving what I'm going to talk about so I'll move ahead talking now looking at these eruptions from the Sun connected with solar flares the sound is actually a very inactive startup compared to many stars out there uh we it's a dwarf star um and things about our solar system are not very eruptive like this thankfully for us I think but uh what we've got on the sun of this the Sun as you know has not got a solid surface but it's a gas ball and it's rotating not this fast in this little x-ray image up here uh it rotates at 26 days at the equator and at 30 days at the poles this means it's differentially rotating and if you differentially rotate a magnetized plasma it's like winding up a basket full of rubber bands eventually they start springing out and here are the rubber bands that the magnetic field lines springing out from the surface of the Sun in this picture down here taking in the ultraviolet but sometimes there are really enormous eruptions on the sun so-called solar flares and uh perhaps the brightest solar flare seen in uh historical times was recorded by RC Richard Carrington Esquire well engaged in the four noon how many of us talk about the four noon of Thursday September the 1st in taking my customary observation of the forms and positions of the solar spots the appearance was witnessed which I believe to be exceedingly rare and that is in this drawing here it's these white bits just here and what we refer to as a white light flare now white light flares on the side are very rare he's the only one to have seen one and it was verified by somebody else so it's a genuine observation but it coincided with the observation of the Aurora this is a painting of observation of the Aurora as far south as the Caribbean also back in those days they had telegraphs connecting cities that ran along railway lines on things they were long wires and people were getting Sparks off them and things was being set on fire by them this is because there was an enormous eruption from the Sun at the same time or plasma coming out directly towards the Earth and that plasma striking the earth a few days later giving rise to all these phenomena essentially what you've got is the Earth's magnetic field is encased in this solar wind all the time but there's a big eruption passing through it it squeezes the Earth's magnetic field and everybody knows from Faraday's Lord if you move a magnetic field you generate an electric field and those electric Fields lead to all of this phenomena and also the Sparks and were one to happen today it could easily wipe out many of our transmission systems and wipe out our satellites particularly the GPS satellites the next time one happens um they're not predictive we can't predict when they occur the next time what happens I don't want to be landing in an airplane now it was thought that these were extremely rare and haven't happened recently but actually we have got two satellites monitoring the sun one ahead of us in our orbit one behind us in our orbit by about 60 degrees and they're called stereo a and stereo B you're now seeing the whole of the July the 23rd 2012 that's the sun in the center it's just a it's not an image it's just an image pasted on this is a disc blotting out the image of the Sun and you can see in this speeded up movie you can see that something is erupted from the Sun here it goes this vast coronal mass ejection it's called but notice how that this image suddenly gets terrible it's full of spots that's because there's a vast cloud of very energetic particles coming out as well and those energetic particles which come out only slightly slower than the speed of light are them bombarding that satellite with this intense uh erase it's very intensely irradiated that's what causes a lot of damage to satellites it's what we don't want so this was 23rd of July 2012 had it happened just a week earlier it would have happened directly at us so 2012 would be known to all of you this date would have been known to all of you had it happened uh well or let's say it would be 16th of July 2012 would be known to all of you if that the alignment are being different so are solar flares the biggest things that happen on the Sun well this is just a technical plot but this is the frequency at which flares occur versus their energy and don't worry about the units uh but what we've got each of these ticks is a factor of 10. so you know this is 10 to the 24 10 to the 26 that's a factor of 100 that's a factor of 100 that's a factor of hundred in order to plot anything and I'm going to show you only a few plots but I'm going to talk about big numbers and the only way I can talk about big numbers in astronomy because they are astronomically huge is to talk about them in powers of ten so when I say 10 to the 20 that means a 1 followed by 20 naughts 10 to the 40 is a one set followed by 40 norts 10 to the 52 Watts we're going to get there 10 to the 52 watts is a 1 followed by 52 zeros Watts well here we're talking about 10 to the 32 uh this is the total energy in a flare and you see people have looked at the rate at which flares occur there do they also occur up here well you can if you work it out these flares up here where they to occur would occur once every thousand years or so so we have to look at the sum for a thousand years to see one of these super Flats but another way to do it is to actually look at a thousand stars like the sun for a year and that's what's been done with the Kepler satellite just staring at a thousand solar type stars and they do see these flares and it continues up there so we don't quite know where this ends and there's probably some physical limitation but they can be extremely energetic and this is just a dwarf star unlike the sun it's smaller than the Sun a small red dwarf star actually have a flare that big in 2014. now I'm going to go on now with I'm doing the preliminaries before we get into all the exciting details and all the powerful events in the universe I want to talk you through a little bit about what I what what how big Power can be how much how large can you think about the maximum power and I'm going to send you all out of the room because I'm going to give you an equation which everybody says one shouldn't do but this is a very simple equation it's just what is the maximum power that you can get from an object of mass m and so it's very simple but if you've not seen it it's very tuned as at least in terms I think it's cute but this is the power or luminosity it's it's defined as energy divided by time we all know about light bulbs 100 watt light bulbs or 15 watts light bulbs that you use so that's that's a unit of power so it's energy divided by time what's the maximum energy you can get from Mass m Einstein gave us the answer it's m c squared and I'm sure everybody in this room knows E equals m c squared so there's energy equals m c squared what's the shortest time then you can get it out on it's what we call the light Crossing time it's how long light takes to cross the object because the fastest you can remove the energy is at the speed of light and of course if you want to get a a pulse from it you've got to have the light from the back side Andrew God would see the light from the front side and there's a time difference between the two so that's R over C rearrange that we get m c cubed over r and then what's the smallest radius it can be what's the smallest radius a mass can be it's a black hole what's the side of a black hole it's GM over c squared if it's spinning okay so I now rearrange it and the N cancels and I get C to the fifth over G and that's the maximum power that you can generate from an object C to the fifth C is the speed of light which is a very large number G is the gravitational constant gravity is not a very strong force it's a small number a very large number divided by a small number it turns out to be 3.6 times 10 to the 52 Watts okay that sounds utterly ridiculous utterly utterly ridiculous but uh it's not completely ridiculous it turns out to be the maximum power is 10 to the 26 times the Luminosity of the Sun okay now it turns out that in our galaxy there's a hundred billion stars and there's about a hundred billion galaxies in the universe so if I take the power of all the stars in the universe and they'll add them all together that's going to be 100 billion times 100 billion that's 10 to the 22. so this maximum power is 10 000 times bigger than all the Luminosity of all the stars in all the galaxies in the universe but this is my maximum yeah another limitation on power in the universe comes from what we call the Eddington limit 100 years ago one of the most prominent astronomers in the last century was Arthur Eddington a plumbing professor in the here in the University of Cambridge this is named after Eddington pointed out there's a limitation to how powerful something can be because power that because radiation and if you've got something radiating radiation exerts a pressure we've all seen pictures of this this is this is Comet hail Bop that the older members of the audience will remember from uh about 20 years ago this is its tail or tails this is the so-called Iron Tail which I'm not interested in this is the dust tail and basically the sun is way over on the left here and the radiation from the Sun is blowing the tail away from the comet and this is very visible visibly demonstrating that radiation pressure can push things and what you can get there's a limit to how powerful something can be in terms of radiation when the radiation is so powerful it blows the thing to pieces so that if radiation outwards is equal to the gravitational pull inwards um or it is sorry greater than the gravitational pull inwards then obviously the object will blow itself to pieces and that's called the Eddington limit when you're there and this is a plot showing power up there versus massive objects in the universe and I'm again using this logarithmics unit so zero means one let's turn to the naught that's 10 billion and so on the sun's down this bottom part this is the heading to limit there's the ultimate or maximum power and it turns out stars are down here galaxies up here and all stars in the universe up there now we're going to start thinking about exploding Stars ah so I'm in order to talk about exploding Stars I want you to think about what stars are and what's going on in stars and I'm going to do this in terms of this Mass radius plot don't get too worried about it but this is mass and radius that astronomers like plotting everything in the universe all on one plot and so we've got logarithmic units again okay and stars are over here with the sum there on one one of these units and these are black holes these are planets and when you get up here this sort of turns around it goes down to these objects called white dwarfs incidentally why dwarfs were first understood by the Master's grandfather Ray Fowler this Turning Point Here is known as the Chandra Seeker Mass that's there's a maximum Mass to a white dwarf and it's up here down here there's another point at which things you can have stable objects these are this defines where stable objects occur why dwarfs planets that's Jupiter that's the Earth and neutron stars are over here just before you get to black holes there's nothing that is made that what we would see is a solid object and above in this part of the diagram above the white dwarfs and neutron stars you then have the black holes which are objects which I'll get to later where they've collapsed in on themselves stars are over here and they're held out over there because they have nuclear reactions in their cause which have generated pressure in them which balances gravity and so in the sun we've got the outward pressure thermal pressure due to the creation of all the helium in the core of the Sun from the hydrogen there nuclear fusion that's actually inflating this the sun keeping it in balance and the sun's been like that for the last five billion years but eventually you end up using up all the hydrogen in the core of the star and it then collapses the core collapses and starts burning helium to carbon and eventually the sun will die as a carbon oxygen white dwarf so there I've represented this by an arrow the sum will end its life as a white dwarf it will throw some of its outer envelope away but it goes like that and it will get stuck on that bit there but if you're a more massive star somewhere up here then what happens is the only thing the core of the style can do is collapse all the way down and form the black hole there's nothing else for it to do and in doing so because the material of the star the core of the star there's collapses inwards there's nothing to stop it collapsing down and there's an enormous amount of energy being released and it does it very quickly it collapses down in a matter of uh minutes and seconds enormous amount of energy vast explosion that's what we call a supernova explosion there is just one other one of these and that is if you're a medium-sized star then you can actually go across here throwing off some of the mouse on the way and you can end up as a neutron star so I'm now going to introduce you to supernovi and neutron stars starting off with the only Supernova that's the Supernova explosionist that star exploded that's what it looked like beforehand it's this thing in the middle this star exploded in 1987 in February in the nearby Galaxy called the large magellanic Cloud it's a satellite Galaxy of Our Own this nebula is a nebula of gas and you can see it in the light of hydrogen there it's called the tarantula nebula because it looks a bit like a squash spider anyway this thing was extremely bright and visible to the naked eye it's the last one that's been visible to the naked eye and this is just a plot of its brightness versus time that's in gear and you can see the thing actually was not observed down there and then suddenly very quickly it brightened up and made this brightness and drop down like that and when it's below this level it's two fate fate for the human eye I actually was observing at the anglo-australian telescope in late 87 and saw this Supernova through binoculars well it didn't come early enough to see it with the naked eye so I've not I've never seen a naked eye uh Supernova the this part of the curve in this plot which is straight like this is due to radioactive decay when you get a supernova explosion the temperatures are extremely high and they go and uh in the ejector as it's all thrown out there are lots of neutrons and that leads to many of the heavy elements uh the elements greater than hydrogen helium that we have around us most of us are the I don't know if you know this but the dominant element in your body by mass if I was to go around and ask you most people would say carbon actually you're wrong is oxygen okay now if I was to get a stone and do the same what's the dominant element in a stone it's mostly oxygen I'm the geologist in the front there is nodding in approval so I think I've got that right anyway uh so so oxygen but in our bodies okay most of the oxygen in our bodies was formed in one of these Supernova explosions so you know all of this we are star dust etc etc but that's where most of the oxygen comes from and about half of the iron in your blood comes from what's called a core collapse Supernova these are the supernoving where the core of the Stars collapsed as I've shown you and and this is a wonderful image is made by the Eros II collaboration and this is speedied up images of the region the Supernova occurred here and this is this is uh speeded up images over the subsequent over the seven years from 1996 to 2002. could you see these ripples going outwards these are just where the light from the Supernova is now reflecting off the nebulae here okay these nebula have got dust in and if you shine a bright light on Dust it shows up and it can reflect and so you're seeing the reflections and you can see them going across here so they circle around there so in a way this means you can look back in time if you see that and you can actually go and measure its color and so forth you're actually looking at a reflection of the original supernova so when you're out there in a clear night and you shine a torch around that torch light goes out into space and may reflect off uh dust grains and if your torch was really powerful you can see it back again but these you can see this is a another cold collapse Supernova in our own galaxy in the constellation of Cassiopeia and this occurred in the um 17th century and it's not clear that anybody saw it there's still a squabble about whether anybody saw the flash from it but you can see the outer shock wave as it's propagating out into the gas between the stars and you can see the inside of it there now there's another class of supernovae I just wanted to mention because I'll be talking about mergers of binaries again later in the talk and this is these are white dwarfs I said how the Sun is going to end its life as a white dwarf now our sun is unusual in a way because it's a single Lone Star most stars in the galaxy more than half of stars in the galaxy are multiple Stars meaning there's not just one star there's several stars and sometimes there are two stars which are close together and both of them can evolve and become white dwarfs and they can be driven together by the radiation of by gravitational radiation which is something I'll get to near the end of the lecture and they can spiral together like this and when they do that it needs to a giant thermonuclear explosion where the brightness when it goes bang is about a billion times as bright as the sun that's his power not how bright it appears to us but is a billion times the flat the loop power from the Sun and there is a nearby Galaxy M82 with uh before and after when a supernova occurred back in 2012 in that Galaxy and that was this kind of merger of a white dwarf uh supernova and those supernovae mostly leave iron behind and the other half of the iron in your blood comes from that kind of supernova now the brightest flash that's been recorded by anybody flash to the eye occurred at the generation of this Supernova Remnant this is the remnant of the Supernova that occurred in 1006. and it was seen uh The Flash the Supernova explosion was actually seen by Korean Chinese and other astronomers and recorded and uh that's where it where it is now this is the remnant of a uh Paul collapse even over and it's called The Crab Nebula because Herschel thought it looked a bit like a um crab but I I can't see that myself but uh it's a very strange object and this is the remnant of the Supernova that occurred in 1054 A.D um this is in the constellation of Taurus and when it was going off it would have been easily visible in the daytime there are absolutely no records from England um maybe everybody was going around looking at the ground all the time or maybe it was cloudy all the time but uh anyway it it was not seen but it was again recorded by uh Asian astronomers and I think it was also recorded by some monks in Switzerland now this Supernova of AD 1054 which is only 48 years after the 1006 one so it was possible for somebody to have seen two supernovae in their lifetime um this this one has left behind a neutron star and it was long thought that there's something funny about one of the stars in the center of it and it wasn't until 1968 it was realized it was a pulsar a pulsar is essentially this collapsed object to the center only it's highly magnetized and as it spins round it flashes at us and it flashes in all wave bands from the radio through to the um gamma-ray bands and here is this is the Pulsar that thing there and you can see that it's done something to the nebula around it and that's because it's a highly magnetized neutron star the neutron star has got a size of a radius of only 10 kilometers so it's about as big as London it's rotating at 30 times a second so it's going spinning pretty fast and it's got a magnetic field of a million million Gauss or million billion times that magnetic field in this room I'm now going to just play you what it sounds like that's 30 times a second there are pole tiles out there that are much faster and I'm now going to remind you of last your last visit to the dentist because this one is 600 times a second you ready [Music] I thought you'd like it so these are pulsars pulsars are the dead remnants of um explosions uh exploded massive or medium mass stars and they're quite common in our galaxy that are also kinds of neutron stars which have got extremely high magnetic fields there are a thousand times higher than the one I just talked about so there are a thousand billion billion times the magnetic field in this room these extremely high magnetic veils mean that the crust of the star is incredibly stressed by the magnetic field and sometimes it cracks and breaks and that leads to an intense flash of radiation most of it in the gamma ray and hard x-ray bounds and these objects are known as magnetars and this is the most intense flash that's ever been recorded most powerful flash well it's it's the brightest flash this one and it occurred in 2004 in December and this is just a time running along there where that is a minute another minute and so forth and this is this incredibly intense Flash and indeed that that in this instrument it's totally saturated and the only way they got good measurements of the brightness of this flash is by looking at gamma rays reflected off the Moon and the Moon is not very shiny at all in gamma rays in fact it mainly absorbs them so this is a really intense Flash and as I say it's it's the brightest flash that's been seen and it comes from the other side of the Galaxy and as it decayed it showed a pulsation okay can you see the pulsations there every five seconds that's due to its spinning um these flashes of gamma rays hitting the Earth's atmosphere ionize the atmosphere and indeed the oscillations could be picked up by radio measurements of the outer atmosphere either outer ionosphere of the Earth so it set the Earth's outer atmosphere ringing like a bell so something the size of London the other side of the Galaxy goes bang and causes our atmosphere to ring like a bell okay if you wanted to do real astrology we should all do gamma-ray astrology because these are the things that really do affect you I'm absolutely 100 convinced that the position of Saturn in the solar system of the day you were born has got no influence whatsoever any influence whatsoever our new personally I'm now going to turn to black holes and just to show you the evidence for the one in the center of our galaxy these are all stars in our galaxy this is the Milky Way the dark bands are due to dust and the center of our galaxy is there everything in our galaxy rotates around the center at about 230 kilometers per second if you go in and look at the cluster of stars at the center of our galaxy particularly in the infrared band you could it's this is where the center is just there you need to remove the flickering the the deviations caused by the Earth's atmosphere in order to do this and this is called Adaptive Optics where basically you have you create a star and the atmosphere outer atmosphere of the Earth and you sharpen your images up on that and as they switch it on you can see the image gets very sharp here so that you can actually see the motion of the stars um we make the artificial star using these laser beams these are the Keck telescopes on Hawaii shining laser beams at the galactic center the galactic center is 25 000 light years away so if they were to send a signal it would take 25 000 years to get there so I don't think if there's anybody at the galactic center where they're going to take much notice of that but anyway here is what they can see in terms of the motion of the stars and you see the stars are doing something moving around the center here if we now look at that the these are the actual a plot of all the motion of those Stars and there's one of the Stars I'll go back it's this one is orbiting this Center about once every 15 years and that's this star and when it was going close to this point it's orbiting around this point in an elliptical orbit when it's close to this point it's traveling at 4 000 kilometers per second this is the radial velocity of it and these are the positions of it using Newton's equations of gravity you can work out the mass of the object there that mass turns out to be four million times the mass of the sun four million times the mass of the sun and yet it has to be a very compact region because it follows an orbit very precisely how compact does it have to be it has to have a density which is more than 10 to the 19.5 times the mass of the sun per cubic parsec you probably don't know what a cubic parsec is it's a distance measurement in astronomy but essentially its distance apartheid is the distance between us to the next star approximately so our local density of stars is one in these units this is a hundred million million million times higher than the density locally to us it can't possibly be made of stars because it will be incredibly bright he can't even make it out of neutron stars without the neutron stars colliding with each other there's nothing known to physics that can be there other than a black hole now black holes also are powering quasars but let me go on to the concept of the black hole this is from Einstein that the idea that Mast warps space-time and here it's shown warping the space in just in the two-dimensional representation and it's something where the the the center has collapsed but warping the space around it and there is an event horizon around it a little bit like a water portal this is Niagara Falls of course but you've got to think about this Edge round here as being a point Beyond which you you can't come back and we call that the event horizon as you approach The Event Horizon and are observed by an outside Observer and you go from looking yellow to Red you appear red shifted and eventually time appears to stop if you rather clock your clock would appear to stop by the time it gets here you never actually appear to the outside Observer to fall into the black hole so black holes were originally a theoretical concept and originated in the 1780s by John Mitchell who was a fellow of Queens College but spent most of his time looking after a parish in Yorkshire but he theorized that if he was to pack lots of sons together lots of stars together eventually they would have an escape velocity from the surface bigger than the speed of light and therefore you couldn't see them that's a Newtonian argument which isn't right nowadays but uh he essentially got the right answer but then Einstein came up with his general theory of relativity and that gave rise to the concept of black holes that the the equations were solved the following year just a hundred and one Years Ago by Carl schwartsfield for us a stationary Point Mass and then for a spinning object back in 1963 by Roy Kerr I now want to show you about black holes by just showing you a picture of the sky this is the visible sky and if there are any amateur astronomers amongst you you'll recognize this pattern this is the constellation of Orion with Beetlejuice there and rigel there and that's the brightest star star in the sky serious this is the moon and that's the constellation of Taurus the Bull I'm going to switch now to walk the sky the same patches guy looks like in the X-ray band there it is and then you can see the stars of Orion's belt flip back you can see Orion's Belt and they're showing up because of magnetic activity like we can see on the sun you cannot find Beetlejuice in this picture the Moon is that thing this bright thing here is the Crab Nebula which I've already shown you which has got the Pulsar in it's just a dead star and this is serious but not serious a this is its white dwarf companion Sirius B so in x-rays you see Sirius B not this bright star which is serious a you know they almost each other every 50 years so in this picture in x-rays you see dead objects white dwarfs neutron stars some active Stars magnetically active stars and many many black holes most of the objects you can see are black holes and here we can see black holes now I've just said things can fall into a black hole and you can't see them they can't go out how can you see black holes you see black holes because material falls into them they are the ultimate thing to drop material into and you can release the greatest amount of energy by dropping material into a black hole and this is just an x-ray image of a patch of sky and 95 percent of the dots there are black holes accreting material from their host Galaxy some of these things are clusters of galaxies they're big fluffy ones there is an artist's image of one of these black holes creating material in the form of an accretion disk we expect the matter to swirl around and sometimes the magnetic fields generate powerful jets that come out of them so accretion dropping matter into black holes generates enormous amounts of power and just to go through some numbers with you this is equals m c squared but with an efficiency factor and in for chemical reactions that is 5 times 10 to the minus 11. it's a very small number chemical reactions are very inefficient and it equals m c squared nuclear fusion is a hundred million times better and that's what powers the Sun so clearly you're getting a lot of energy out for your mass and indeed if you were to uh you you take your petrol from your car and uh enable it to undergo nuclear fusion rather than chemical reactions you go 100 million miles per gallon or should we say a billion miles per gallon you can go even 20 times better than that if you can go to black hole accretion if you drop matter into a black hole you can release more than 10 percent of its response so small amounts of matter in galaxies falling in to black holes at the centers produces an enormous amount of power I've shown you pictures of the black hole at the center of our galaxy it is not very bright somehow it's not that much material falling into it in many other galaxies they are very bright and what they do in this brightness is uh essentially blast all the gas out of the Galaxy and we think that this is the reason why many of the elliptical galaxies the most massive galaxies in the universe are mainly these big pools and stars they all look now red and dead unlike spiral galaxies we should got lots of star formation we think that's because the black hole at the centers of these galaxies has blown all the gas out of the Galaxy in Blowing all the gas out of the Galaxy they stop any new stars forming there's no gas to form new stars this is amazing this is been a realization in the last 20 years is the black hole at the center of the Galaxy that controls the mass of the whole galaxy when a Galaxy ends its life is due to this tiny little thing spatially tiny it's actually got one thousandth of the mass of the Galaxy but it's physically very tiny it's got a size the black hole at the center has a size compared to the size of the Galaxy a bit like the size of an orange compared to the size of the Earth okay that's on the extreme for you okay imagine something that small controlling something that big it's got a thousand for the bass but small amounts of matter falling into it blast all gas out of the Galaxy that's what we think is happening in quasars moving on there are these jets that come out of them often powered by the magnetic fields and if we happen to look down the jet those objects can look even brighter so this is very bright but if you look downward it's going to look very very bright and actually one of these objects act quite High distance and for anybody who's an amateur astronomer they might know about redshifts and redshift one there was a quasar redshift one visible in binoculars just over Christmas because it's jet pointing at us underwent an enormous flare these Jets can go out beyond the galaxies this is a large Galaxy and is squirting these Jets out either side making these enormous lobes this is actually emissions seen in radio wavelengths overlaying on an optical picture of that region now these Jets can lead to interesting phenomena this is the nearest jet that has been seen it's in the consulate it's in the constellation of Virgo in a galaxy called m87 and here's this jet sticking out that side you cannot see a jet the other side this was found a hundred years ago by Hebrew Curtis who wrote that there is a thin white ray emerging from the nucleus of m87 he didn't know what it was and you know we don't actually know exactly what it is even now a hundred years later we know it's squirting electrons out we know that because of all sorts of things including the fact light is polarized I'm not going to Define what that is if you don't know but basically that means it's got negative particles coming out we don't know what the positive particles are coming out whether they're protons or positrons maybe it's squirting antimatter out I think it's squirting antimatter out which is rather interesting we cannot see the other side we think their Jets going out equally either side we can see that one why can't we see the other one well we can perhaps start to understand it if we see look at this Hubble image of it it's been tipped rounding to make it level here and there's the jet I've just shown you there we're going to look at this bit of it here and can you see in the 90s Hubble saw there's clearly something emitted and has moved across like that if you work out the distance it's moved it's gone 24 light years he's gone 24 light years in four years so he's troubling at six times the speed of light okay is that all right I'll have one of those please because you know that's how I can travel around in space it's super luminal It's actually an optical illusion even those ripples from the Supernova were traveling faster than the speed of light okay it's due to the fact in this case that this jet is pointing towards us and the matter in the Jets is traveling very very fast it's going very close to the speed of light it's chasing the light beams and you can do a very simple geometrical calculation which I am not going to do here show that you can end up with this apparent super super luminal motion now the most amazing jets that we see are these ones and they're associated with gamma-ray bursts these are intense flashes which were first found in the 1960s by the military both the Russian sorry the Soviet and the U.S military were monitoring outer space hoping to check that each other were not letting off nuclear bombs in space these are monitoring satellites they did find flashes of gamma rays that you would expect to see from a nuclear bomb accepting these flashes of gamma rays clearly Came From Beyond the solar system they did not come from nuclear weapons I mean people did at one point say well maybe their other intelligent life as netting off nuclear bombs but no that's not the answer these flashes like this are associated with the birth of black holes in Stars and basically what happens is during the Supernova collapse forming a black hole if the material is spinning very fast it's able to make jets which squirt through the whole star and out through the star and if it's shining at us and I'm not going to point this laser beam at you but you know a laser being pointed is very bright along the laser beam it's like having a laser beam Shone at you that's what we're seeing here these things are very bright in gamma rays the gamma ray bursts and for anybody who knows about relativity these Jets have got a lorentz factor of a hundred and this thing has got a Lorenz factor of 10 but I'm not going to go any further in defining it these are extreme objects in the sense they're got extreme powers now I'm going to I'm on my last 10 minutes I'm going to go through two final classes of objects these are fast radio bursts they're the mystery of 2017 they made the cover of nature in January the first issue of nature this year these fast radio bursts were discovered in first discovered in 2007. these slides were given to me by Jason hessels Over The Duchess astronomer um now that's the parks radio telescope here in in Australia and it picked up intense flashy at one intense Flash in 2007 that's when it was published by Duncan Lorimer so known as the Lorimer burst it's an intense very bright flash these are hundreds of that's a hundred milliseconds 200 milliseconds so that is half a second so it's a very sharp flash it also change this is now frequency and it changed in frequency so essentially in radio frequency it was first detected at high frequencies and then you know it decayed and was seen in the lower frequencies this is called dispersion of the radiation is characteristic of radio signals going through ionized gas and this looks like it could be the gas between the galaxies or it could be gas associating with the thing itself apart from the fact that the radio telescope was pointed at a particular region they uh Duncan Lorimer had no idea what this is due to it was clearly very sharp and very bright people then begun to wonder whether they there were any other ones time passes people are getting frustrated they can't find any more bursts nobody found any more bursts and then there were some bursts seen also from the parks radio telescope they looked a bit like the original one accepting they were a bit sort of spotty there's something funny about they don't quite look right and what they were due to was somebody opening a microwave door nearby it took a while to work this out but they're pretty certain that this one is not due to a somebody opening a microwave door okay and so it remained as a big puzzle what the what's going on here until in 2013 another burst was seen or and a few other this meant there's a population of fast radio bursts people didn't know what they were because these radio telescopes are only looking at a tiny patch of sky there must be thousands of these over the whole Sky per day but what are they and you could these are all the ideas are they pernicious radio frequency interference or atmospheric effects flare Stars we've already heard about flares are the micro quasars pulsars magnetars or are they Shetty are they little green people okay can they be something new gamma-ray bursts supergiant pulsars from pulsars evaporating black holes for Stephen Hawking supernovae uh merging black holes I'm going to talk about that in a minute we don't know and then another one was found from the Arecibo telescope you can see it's not a great one but there it is and this is the start of making working out more what they are this came from this Arecibo telescope which many of you will remember if you like watching Bond films they they falls on here during the film and which film was it hmm GoldenEye well done thank you chefs yeah I always remember the eye bit because this is an eye on the sky okay so there we are um anyway it came from there okay now this is a globular class this this is the plane of our galaxy The Milky Way so it came along the plane of our Gallup Galaxy but it's not obvious it's galactic and then they found more from the same position so it's not due to a cataclysmic explosion something blowing itself to Pieces it's repeating and um you can see there are many more of them you you may wonder why they're not all shaped like that that's because somebody's straightened them all up just to pack them all onto a simple plot so really important it rules out the cataclysmic Source it's not a single explosion it's due to a pulsar on steroids perhaps and they even worked out where it came from because it repeats they even found there was a constant Source at the same position they were able to combine a whole load of radio telescopes Arecibo and the European vlbi Network and there's a map of it and you probably can't read this but this one here is it it it's uh this one is Cambridge so anybody who drove up the Barton Road will have driven past the telescope the big The Big Dish there is part of this uh this European very long Baseline interferometry Network by using all these telescopes at the same time looking at the same patch of Sky they can get a very accurate position foreign this object okay it came from that object and you can see it doesn't look very exciting does it so this burst came from there this is the cover of the first nature of the year um and uh so this is where it comes from it's a very faint object it's a hundred million times fainter than the naked eye limit the Galaxy it comes from is a thousand times less massive than the Milky Way I showed you that Supernova 87a came from the large magellanic Cloud the small magellanic cloud has about this Mass so it came from a little tiny Galaxy and each Burst when it goes briefly outshines all the other stars in the galaxy and it looks like this object is the small magellanic Cloud only at three billion light years so these bursts we're looking at happened three billion years ago thank you what are they we don't know uh I think many people think they are actually due to a very young magnetar okay if magnets are were formed you know maybe 20 years ago we don't we never saw a supernova from there but then maybe we wouldn't have done and uh maybe it's left behind one of these magnatars it remains a puzzle now into the last part uh one other class of flair that you can get is when a star Strays close to a black hole and is ripped apart by the tides I don't have time to talk about those but I'm going to talk now briefly about gravitational waves when you get binary Stars spiraling together when they orbit each other they cause warping of space-time and they cause gravitational radiation and this is meant to represent ripples of space-time flowing away from this binaries system you can get binary styles of different types white dwarfs we've already spoken about but you can also get neutron star neutron star binaries here they are and these are the temperatures so going up to 10 000 no 100 000 billion degrees when you merge two neutron stars together like this you probably get a gamma ray burst and you also generate a lot of heavy elements it turns out that in the generation of these heavier elements I've talked about oxygen I've talked about iron but it's very difficult to get significant elements Beyond iron out of supernovae and there's been a big puzzle where gold comes from I've got some gold you many of you will be wearing a bit of gold that's where they come from neutron star neutron star mergers that's the only way we can explain gold and when they do this they generate a significant mass of gold about the moon's mass of gold now before you sort of are thinking about a gold moon it's probably spreading a load of bits and uh it'll be a very difficult thing to get hold of but anyway I'm just trying to say many of the things I'm talking about are actually connected with you not you in your current form but the atoms out of which you were made and the atoms out of which your jewelry is made now go on to the final one this is the ultimate one this is the gravitational wave merges of black holes two black holes can spiral together and as they spiral together they go faster and faster and then leave behind a black hole and the ligo Virgo Consortium have got instruments now which are the ultimate rulers which rulers in the sense of you know measuring inches should we say um these things are this is ligo which consists of this Cross of laser beams are shining up there shining up there they are comparing these laser beams all the time if you stretch that and don't stretch that one then they'll get out of sync and you can detect that down here and you can detect changes in length equivalent to an atom the size of an atom versus the distance between the Earth and the Sun that's that's the Precision that they're making okay with these gravitational wave detectors 10 to the minus 21. okay and they switched a translago on in September of 2015 and within three days they had measured a merger this is what it looks like there's the oscillation this is just a plot of a theoretical plot of The Strain that's uh that the relative loot motion of it you can see the oscillation gets faster and faster as these two spiral close closer to each other they merge and then ring down and so we've got it like this just to show you the data here's the data like that you can see this is frequency that's time you're seeing it for only 0.2 of a second but there's a it starts off with a frequency of somewhere like 40 Hertz and at the end it's gone up to almost 300 Hertz and this is this detector which was in Hanford in Washington state and this is the detector they had in Livingston Louisiana so they've got two of these interparameters in the US and they were both working at the same time they both saw the same signal and in fact you can take the signal from that one and plop it on top of the signal from that one and you see that they match so they're looking at the same event they were extremely lucky because this was the merger of two 13 solar mass black holes two black holes of 30 solar masses merging together and they presumably formed one of a mass of about 60 solar masses I say about because three solar masses was lost it went into radiation not into electromagnetic radiation it went into gravitational radiation and this is where it sits in this plot is the ultimate power is gravitational waves that merger is up here I've put it at low mass because it's 30 solar mass objects I've given it green because it's not electromagnetic it just for 0.2 of a second the amount of power out of this merging system in terms of Rippling space time the power involved exceeded by more than a factor of 10 the total power from all the stars in all the galaxies in the universe so that is it got within eight percent of the ultimate power C to the fifth over G I've now put everything else I've talked on about on this plot there are quasars apparently can look brighter with jets Supernova gamma-ray bursts supernovae actually most of the power of a supernova comes out in neutrinos and the 1987 a supernova collapse did create neutrinos of which 30 were detected on Earth neutrinos if you know anything about them you know that they're ghostly particles which can go can go right through the Earth many times so that that sort of power there but this is where power lies in the universe and I'll just uh I'm going to finish with a demonstration but this is just a uh again representation of two black holes merging if you were close enough to look at them against the Milky Way uh it would look a bit like this you wouldn't want to be this close but um okay and here it goes we get closer and closer and space-time stopped wriggling and there we are okay and there's just a nice picture of the Milky Way there's the large magellanic cloud and there's the small magellanic cloud now I'm going to show you just a chirp what happens the oscillations go faster and faster and then stopped that's called a chirp and that device I'm about to show you actually produces a chirp and you this is your take-home experiment okay okay now don't be worried about it's actually a toy don't be worried about playing with toys these are three Nobel Prize winners in physics Richard fireman Wolfgang powley Niels ball two great physicists of the last century they're looking at a toy is the top a tippy top one that you spin and it flips over if you know what I mean and they're trying to work out what's going on this guy Richard Feynman was actually watching somebody spinning a plate in the Cornell cafeteria and realized that the motion of the plate was peculiar and he worked out what it was doing and in his autobiography he points out that it that took in broke through in his thoughts and ideas that led to his Nobel Prize so what I want to do now is to show you a simple toy and it's uh this thing here it just consists of a heavy disc and just a plate to put it on and I'm going to spin it now and hopefully the camera um will okay it's now spinning you can do this at home with a dinner plate okay do it on the floor of the way in which it gets faster and faster the rate of of change of it is the same rate of change form as the merger of two black holes or the two white walls together so it's going faster and faster and faster and it takes a long time but when you live where do you do the plays on the floor don't worry it will happen quickly then you'll do it again because you realize you had to play it was all the way around and this will end up with a chart and that will be the end of the leg consolation of angle and then from the tips yeah it's uh but I hope you've been seeing the holographic uh thing on top it's uh the actual things that spitting apart from under the parents came from where foreign is my talk which is on astrophysical black holes and the subtitle is black holes at work so um let me hope that this is going to I'm sorry I'm trying to there we are now the concept of the black hole was first introduced by John Mitchell in 1784. he was a fellow of the Royal Society and also a fellow at Queen's College here in Cambridge he went through a lot of simple physics to work this out and you can do it yourself on the back of an envelope but essentially the sun's escape velocity is 600 kilometers per second the escape Velocity is what velocity you would need to shoot matter out if it was to escape from the sun's gravitational field altogether so the escape velocity for the sound is 600 kilometers per second velocity of light is 300 000 kilometers per second uh I'm using modern numbers here but the numbers he used were not that different um this means that if you were to stack 100 Million Suns together so and that don't ask me how you do it but imagine you could um then what happens is the escape Velocity using Newtonian Gravity the escape Velocity would then equal the velocity of light so as you make an object more massive and compact um the escape Velocity goes up and up and so you get where the velocity of light is the little bit is the value of this escape velocity from this object therefore he he concluded that lineup could not escape from this object and therefore we wouldn't be able to see it and he considered how could we see such a dark star and He suggests it would be by its influence its gravitational influence on neighboring stars in other words nearby objects would be gravitationally perturbed by this object and that's how we would infer that it's there so this was a great idea the next real Seb in black holes was with Albert Einstein and his general theory relativity I've got here just a simple copy of a letter he wrote um in 1913 it was 14th of October it's soon going to be the 14th of October 2000 but this was over a hundred years ago and you can see there he's been using about what happens if we have the sun that's Zona so that's the Sun an array of light that goes close to the Sun is deflected by the gravitational field of the sun it's deflected here by 0.8 Arc seconds of Arc and he's getting deflected he's concluding that basically Gravity the gravitational field of the sun would cause a light Ray which normally travels in a straight line would perturbate and curb it downwards now it turns out he's got the wrong answer here within a couple of years after writing this letter he'd come up to his general theory of relativity and in that general theory of relativity he gets a fact a number which is twice that value and actually the deflection of Light by the sun was first measured in 1919 in a famous Eclipse Expedition that led by Arthur Reddington also from Cambridge and that discovery of the bending of light by the Sun was what really made Albert Einstein famous and uh also made people realize that general relativity is probably going to be our explanation of gravity so what the general theory proposes is that basically Mata perturbs space-time not just space as we can see with deflection of light but it also perturbs the time and we can then just to show you now what we know about bending of light this is a picture of a distant cluster of galaxies where there's a very large aggregation of mass in a relatively compact region of space namely this cluster and our galaxy even was put in this picture will be something like this galaxy okay so it's much bigger than our galaxy but there are many many many many more galaxies and many many stars in this region it's perturbing the light from background starts and background galaxies and all these streets you see our background galaxies where their light has been distorted magnified if you like by the enormous gravitational field of this cluster the cluster is essentially acting like a gigantic telescope using gravity to deflect the light I won't go in any more about such images but there are plenty of them out there if you look on the web and want to see them now back to black holes the um with Einstein's relativity he wrote a lot of equations he didn't actually think there was necessarily a solution but a solution was found in 1916 by Carl sparkschild he in Germany was only spent most of 1916 on the Eastern fronts and sadly died of disease there that year but before then he actually had found the solution for a point Mass let's imagine there is a point of matter he solves the Einstein equations around that and he concludes that the base basic effect of the gravity is to wrap space-time around the point mass and it wraps it up so much that you cannot actually see the whole in the the point mass in the middle and it wraps it at a radius which is not which is beyond the size of the point somewhere outside it's all wrapped up into what we call the Event Horizon which means we cannot see the point mass in the middle and that is essentially the concept of the black hole although it wasn't really appreciated as such at the time taking us on even further to 1963 Roy Keller the guy on the right I took that picture at his 70th birthday celebrations in New Zealand these are New Zealander um Roy Kerr found the solution for a rotating black hole now you might wonder how you can get a point Mass rotating but imagine that the object that's collapsed down to make the point Mass imagine that was rotating and as it collapses it's retained its angle momentum so it's rotating you end up with a rotating black hole we call that a curb black hole and that is the ultimate black hole we know about today so these first sharp black hole is one that doesn't rotate it's a sort of singular one and the the curb black hole is can have a rotation and so most black holes are going to be uh rotating black holes now there are lots of it there's an enormous amount of workers being done on black holes many of it mathematical that all to do with the Event Horizon what might be inside the Event Horizon and so forth I don't want to discuss that at all I'm going to talk only about black holes as objects in our universe that we can observe the astrophysical black thoughts this is just a concept just under representation of space being perturbed into forming a black hole I can't draw a similar picture for a four-dimensional black hole three space Dimension time dimension because there's there's no way I can draw it but you get the idea and this is what event horizon is like just showing you this slide of Niagara Falls basically out here you could be in a canoe and you could possibly be pretty good at it you could canoe in the opposite direction and get away from it but there's a point at which it's inevitable you're going to go inside it and that would be like thinking about the event horizon and it's basically the point of no return another aspect about it because I said that you've got spaces warped and so is time basically the frequency of light an object as it pulls towards a black hole that the color of it would change its frequencies are changing the time is changing if for example we had a black hole here and we threw in a clock and imagine the clock was a yellow clock as it fell towards the black hole we would see the clock appear to slow down and it would turn redder until we couldn't see it and essentially what happens is uh if you throw things into black holes they would vanish from view as they approached the Event Horizon now this so-called gravitational redshift is something that's around even around the earth and around any Mass and in terms of the Earth the GPS satellites the ones that give the signals for a Sat Nav they are orbiting the Earth and they're essentially very good clocks which you're Sat Nav detects signals from and it's all working in terms of clocks and timing now it turns out because that's above the Earth's surface then the graph that there's a gravitational blade shift between it and the surface of the Earth if you were at the satellite it would appear looking down at the Earth as though Earth's clocks are running slightly slow and similarly if we look at that satellite clocks we could also expect there to be um they would appear to be running slightly fast and there's a correction has to be applied and it's applied by your Sat Nav the correction is 45 microseconds per day which might sound uh irrelevant but in terms of if you drive around it would correspond to an error of 10 kilometers per day and that is unacceptable with a satna so these Corrections general relativity is corrected for within a Saturn so this is just the time effect that we we've got there now astrophysical black holes have only got mass and spin The Event Horizon is three kilometers per solar mats the known black holes they're known astrophysical black holes are either of Stellar Mass somewhere between three and a hundred and fifty solar masses or their Synchro massive between a hundred thousand and ten billions of the masses there's 102 found just above that limit and there are discussions about ones below that limit the 150 Solar mass comes from gravitational wave work that I'll just touch on at the end of three solar masses well uncertainty is there there may be they may exist outside those ranges and people are very keen to find ones in between 150 and 100 000 but so far they're not being trapped how do we know that the black holes are there how do we observe well the best observed object that best observed black holes in terms of measuring its mass and properties is the one at the center of our galaxy this lovely picture of the Milky Way showing the center of the Milky Way and the constellation of Sagittarius shows you where we need to look we need to look right in the center of our galaxy remember that we live in a spiral galaxy we're all orbiting around that Galaxy the center of the Galaxy at around 220 kilometers per second we go around the earth at 30 kilometers per second and we go around the center of the Galaxy at 220 kilometers per second and virtually all of these stars are doing the same as well we're all flattened into a disc now we can't see into the center because of all these desk clouds but as in Arena's talk that we've just heard if you go into the infrared you can see through the Dust and that's what astronomers have been doing over the last 20 to 30 years and this is what the galactic center looks like at two microns that's the wavelength I'm talking about what they've got there is using Adaptive Optics where what you've got to do is take out the sort of twinkling that in fact that our atmosphere causes unlike predicted objects you're all familiar with looking at stars and them twinkling that twinkling effect is due to the Earth's atmosphere and due to different patches of the atmosphere being at different temperatures is differential revention you've got to try and get rid of that they do that using Adaptive Optics and one way to do that is to create an artificial star in your observing field and then you correct your telescope to make the artificial star perfectly round and small and then you'll correct everything else in the field and to make the artificial star you can use your telescope you've got in your telescope have a laser beam that is shining up and at an altitude of about 70 kilometers at 70 kilometers it can cause fluorescence sodium fluorescence in the very upper atmosphere and create the artificial style so that's these astronomers here are that's not looking at the galactic center but now they're now looking at the galactic center and uh they are going to make this artificial star an in Liberal Adaptive Optics to make this correction and what has come out of looking at this over 30 years is a Total Image like this this is computer generated and you're seeing 30 years worth of movement what they saw was the fact that the Stars near the center are moving look at this star here you see how it's swinging round and going fast there there's obviously something here just about there which things are swinging round you can't see it this is the black hole at the center of our galaxy and this was what was awarded the Nobel Prize in physics last week the Nobel Prize in physics went to Andrea Getz Reinhardt ganzel and Roger Penrose he's a mathematical physicist at Oxford Reinhardt is at Munich and Andreas Los Angeles and they're using these two of The Observers who came up with results such as shown here these are the orbits of the Stars around the black hole and here's that S2 star I showed you going around in a 16-year orbit and here is the the orbit there and this is the focus of the orbit that's where Sage star it's that's the object to the center that's coincident with um that black hole lies there is something there that flickers in infrared and the radio band and you can also see it flickering it in the X-ray band but it's not always flickering there and it's been known about for some years and uh its name is it's the radio Source a that means the brightest that will particular Source in the constellation of Sagittarius and a star because it's got something peculiar about it now you can just choose Newton's laws to solve the orbit and work out the mass of this object and it turns out to be 4.3 times 10 to the sixth solar masses four million solar masses and it's ability to that and uh you can also work out from how good the orbit is around here imagine that this is a distributed object what is it the minimum density it could have and that density turns out to be 10 to the 19 and a half Stars per cubic Concepts stars of the mass of the sun now that is a phenomenal density remember the local density of stars around Us is around one per 10 cubic parsecs now a parsec is an astronomical distance and it's roughly the distance and they're they're a style and we're in a very isolated patch so it's very difficult to think what else you could put there and indeed you can't even put a a can't put 20 10 to the 20 neutron stars there or anything like that they would all collide with each other and make a terrible mess the only thing now under physics that can't fit in there is a black hole and um I've just shown that plot that's showing the velocity you can measure from spectroscopy the velocity of the stars and you can see the velocity of that particular the star goes up to four thousand and so forth back this August 2020 the group led by this person here Florian um found an inner star s62 was actually moving faster but then the S2 star S2 is here a bit further out this one's quite a bit further closer into the black hole and at its close approach closest approach it's traveling at eight percent of the speed of light it's traveling at like 25 000 kilometers per second so there's clearly something very special in the center of our galaxy and this s62 star is pushing those dances up by a very large amount I think there are basically very few physicists and astronomers who think this is not a black hole what about all the other galaxies let's look at this field of stars and galaxies all the fuzzy objects and galaxies at the point sources are stars in our own Galaxy now this is a big Galaxy this is the actually the center of what we call the Virgo cluster and it's the nearest cluster of galaxies to us it's about 50 million light years away and this large Galaxy at the center of it m87 we're going to look at two but what about that has that got a black hole in as this one m86 this one m84 do they have black holes in what about this spiral galaxy and so forth well over the last 25 years astronomers have looked at all of these carefully with a wide range of telescopes different wavelengths and concluded that they all have black holes at the centers sometimes they're very active black couples and sometimes they're not we'll talk about what actor means in a minute M 87 is an active black hole that's the one at the center of this galaxy the hat and um it's uh got a jet sticking out of it this jet was first seen in 1970 by this American astronomer keeper Curtis and he's spoke of a light light Ray um seen essential this galaxy notice it doesn't continue the other side it's just sticking out like this and this is quite large and you can see it relatively easily in a relatively small telescope you can see it on a radio telescope because it's we've got lots of radio admission you can't see it going the other side this is because this is the jet of plasma being squirted out of the center by this Active Center this active nucleus and it's squirting out at a relativistic speed of about 10 time it's at 0.99 C and due to special relativity it's also squirting out the other side and you can't see the other side because there's evaporation of light light is if you've thought of an object moving very fast it throws the radiation from it in the direction it's traveling so this is m87 and uh in using the same technique that we heard about in the last talk by evina which is interferometry where you have radio telescopes spaced apart she was talking about spaced about by 15 kilometers there's the Alabama telescope there which may be spaced apart 15 kilometers now we've got to we want to go and look at very tiny things we want to increase the resolution of the telescope by thousands to about a ten thousand to a hundred thousand what we do is we make use of telescopes spaced all over the Earth so there's ones in Hawaii one's in California one in Mexico and number down there and one in Spain and also for calibration they use one of the South Pole they use all of those telescopes together and out of that they got an image of m87 the Santa and this is 50 micro Arc seconds that is a very very very small angle and so they this was the observation in April the 11th but they announced the results last year of this ring and uh this is generally thought of as the image of a black hole this yellow is not the black hole the black hole is the thing in the middle you can't actually see the black hole we can only see matters swirling around it okay you can't see a black hole you can only tell a black hole is there by the motion of material around it just as John Mitchell said now going and looking at many other black holes in many other galaxies uh over the last 20 years we ended up with this correlation which uh for astronomy is a pretty good correlation I'll tell you and it's about got four orders of magnitude down here and four orders are magnet across here and it's a it's a logarithmic correlation where it's jumping by a vector of 10 in each of these axis points and basically it if you look at a black hole of mass 10 billion solar masses it lives in a galaxy that is like 200 times more massive and this is typical for these black holes in in galaxies um and when it talks about the mass of the Bulge it's talking about the mass of the central spherical parts of the Galaxy if it's a sparrow Galaxy we're not worried about the spiral arms we're looking at the Bulge at the center and the ratio between the mass of the black hole to the mass of the Bulge is typically a factor of several hundred I know I want to jump to talking about luminous secreting black holes and they're called quasars and active Galactic nuclei and creating by that I'm talking about Mata falling into the black holes and as it falls into the black holes it doesn't pull just directly radially into the black holes it swirls around the black holes and lots of collisions and lots of friction and they give rise to lots of radiation this is a picture from Hubble of just a field with a quasar in and a bright star this is the Quasar that's the bright star now this Quasar turns out to be a million times further away than the star from the inverse Square law it's therefore a trillion times more luminous a trillion is 10 to the 12th 10 to the 12 times more luminous than the start now another galaxy has got a hundred billion stars in 10 to the 11 Stars so this is ten times more luminous 10 times voluminous than a whole galaxy so these things are often quite distant and very luminous they're very luminous what is going on you can't explain this with Stellar processes in particular the first one found three C two seven three which was found in 1963 and identified by Martin Schmidt and it was the same year that Roy Kerr found his solution to the spinning black hole so 1963 is special for us then here what we can see 3c273 Hubble lineage the same diffraction spikes which are deemed to the Israel that due to the Optics of the telescope um and this is the in the third Cambridge catalog of uh radio sources it's number 273 so it's a radio source as well and this strange structure actually if you look very very carefully with this particularly with other wavelengths like the radio or the X-ray you'll find it continues right back to there it's a jet of materials squirted out again at very high velocities it squares it out from the central object these objects these are known as quasars and 36073 after it was discovered was also it was actually more luminous it's it's 10 to the 13 Sony luminosities it's a hundred times more Lumen than all of our galaxy put together and our galaxy extends it's his Stars extend over a distance which is about 30 000 light years now it was seen that three seaters open three varies in brightness over a week how can something as big as thousands of light years vary on time scales of a week the only way from causality is to make the thing very small it has to be smaller than a light weaker cross it has to be smaller than the solar system this object has to be smaller than the solar system and yet produce 10 or 100 times more power than a whole galaxy it's something very special and we think it can just consists of a very massive black hole into which matter is stringing in fact they're all over the sky quasars are all over the sky let's go back the visible picture of the sky it's very similar to the one avino showed where you can see the constellation of Orion is Beetlejuice rigel uh the stars of Orion the sword the brightest star in the sky is Sirius and the Moon let's now look in the X-ray band x-rays are more energetic photons the visible light by a factor of thousands or ten thousand they look at they come from objects which are a thousand to ten thousand times hotter than Stars stars are thousands of degrees these are millions to tens of millions of degrees they in particular come from very compact objects this is serious in x-rays you're not looking at the same object as in this one it's not the same object this is a binary star simply as a the one you can see does the this is the star in the sky as a companion that goes around it every 49.9 years the companion is a dead star a white dwarf in x-rays that's what you see as brightest if you go here that do you remember there's a bright object up there that's that's the moon but in x-rays the moment is very effect this object is the Trap nebula it's a ex it's the result of a supernova explosion for which a neutron star a spinning neutron star of age which is a pulse dollar so that's what's giving rise to that and basically although you can see some of these stars like the stars in Orion's Belt you can see them because they've got tinled magnetic fields in them basically most of these objects down here are background creating black holes in distant galaxies this is what makes up the X-ray background that I studied for my when I was a student and I didn't know this I was looking at the sum total of all the emission from accreting black holes and that's an xnn image where when looking now this is an x-ray it is satellite um xmm which shows us many many accrington black holes in the sky and and clusters of galaxies and by the way there is an Indian satellite astrosat which is devoted to x-rate astronomy and you can look that up and see some exciting results from there this is a schematic of what it looks like with one of these accreting black holes basically uh the black hole is at the center and material is swirling around it but because of angular momentum everything's sort of orbiting around everything else you can't fall directly into a black hole the Sun is going round the Earth is going around the Sun at 30 kilometers per second it doesn't fall into the sun because you need to get rid of that 30 kilometers per second to do so and indeed our most powerful thoughtful Rockets you see ah just 30 kilometers per second so we couldn't fire the missile into the sun even if we wanted to do that there are ways of doing it but it doesn't involve firing it straight at the Sun and so aglamenton is preventing the matters going into the black hole and it falls into this disc disks are quite common in the universe and these the material in a disk as you go inwards the material in inwards is moving faster than the material outwards and therefore if you've got some friction there's going to be a lot of viscous energy release and it gets hot and indeed these discs get very hot they've also got lots of strong magnetic fields and those magnetic fields get knotted up in the center and they release enormous amounts of power in a region we call the Corona and this is a very bright hard x-ray Source a source of high energy x-rays those x-rays then Shine Down onto the accretion disk and irradiate it and they cause fluorescence which we pull the reflection Spectrum so the Observer sees this hard x-ray Mission and it also sees emission from the surface of the accretion disk and we see that it also produces a very strong ion line and this is a spectrum one of my students made a few years back of the iron line from the foreign we're looking down at the emission which is swirling round and it's going up to half the speed of light which is what happens in accretion flow then we're seeing large velocities and there's a lot of Doppler shift which broadens this iron line and then because we're very close to the black hole there's an enormous amount of gravitational redshift and we can measure that redshift the amount of the redshift we see and the large red shift implies the emission is very close to the black hole if we say the radius of the Event Horizon is a gravitational radius this emission is all coming from within two or three gravitational radii we're looking right in close to the black hole and we can start to understand the flow of the matter that's close in and in terms of this object we can actually measure the spin of the black hole this is just to emphasize if you can measure the red shift then you can start to measure the spin and the way it works just briefly is secretion flow around a non-spinning black hole The slouched Shield black hole which is this one has to stop are basically away from the black hole and then there's an innermost radius and it then plunges inwards and that's due to the nature of the physics but if you have a rapidly spinning black hole it drags the material in right close to it and you therefore get the disc extending much further in and that gives you more gravitational wrench shift so the blue one here has got this and this is x-ray energies and the redshift means it's going to lower energies uh this one is an emission line you'd expect to see from this disc and the red is the one from that disc which is the non-spinning one and we're seeing in the previous plot something like this so we know the spin is very high and okay many of us have been working on this we're coming up with the black hole Spin and black hole mass for a very large number of blank holes and we hope to do more over the coming years now I talked about black holes at work what's going on with black holes when they are in the middle of these objects there's something called black hole feedback I want to talk now about the amount of energy you get out from dropping material into a black hole okay and I'm going to use an equation now E equals m c c uh you will all have that equation E equals n and the basically the rest mass energy of something is um m c squared when you think about chemical reactions there is energy release and that energy is associated uh there is a very tiny change in the mass of the object if you could actually measure it the energy has a mass and that corresponds to 5 times 10 to the minus 11 m c squared that's petrol nuclear fusion is 0.005 MC squared black hole accretion is 0.1 m c squared okay so this means that the difference between these two is 100 million I think the difference there is 20. so this means that if you so that would be 2 000 million or 2 billion so actually if you could have a black fold in your car you could go 2 billion times further on a gallon of petrol but of course you couldn't get a black hole in your car nobody knows how to do anything like that I don't anticipate this being the solution to the energy crisis or anything like that and just making the point here it's this is the most efficient way of releasing energy apart from Pure matter antimatter Annihilation which can achieve mc squared but of course there's very little antimatter in our universe and I would say thankfully there's very little antimatter in night Universe if you want to get very large energies you can get out the mount through black hole accretion it's why when Mata falls into a black hole it can lead to extremely high luminosities and it's something to ponder about that black holes are the blackest darkest objects in the universe and immediately around them they can be the most luminous objects in the universe they're right next to each other yeah now what we can do is look at the amount of energy that's released as we grow a black hole black holes have grown in Mass up to a billion solar masses through accretion by matter falling into them and the total energy release to grow a black hole in the Galaxy actually is more than a hundred times bigger than the binding energy of that Galaxy what I mean by that is how much energy would I need to throw the Galaxy back out into space I mean in in its constituent parts now that means if we can couple some of that energy to the Galaxy we can affect the Galaxy now we can't couple the energy from the black hole to the distant stars in the galaxy there's no way of doing it there's galaxy the stars are far too small and and massive to be you know you can't there's no way you can make them interact but what you can do is to effect affect the gas in the galaxy and that's where this next plot comes in it looks like a complicated plot and I'm sorry about that but it's actually very simple it's actually the space density of galaxies as a function of the mass and it's just a long log and you don't need to look at the units or anything like that so there are lots of small galaxies in the universe a very small fume big galaxies in the universe now naively you would actually expect that the distribution of the space denser galaxies with masks to parallel that a dark matter I'm not going to talk about what dark matter is because I don't know but there's something in the universe called dark matter that only interacts with us through gravity we can't see it which is why it's called dark matter now dark matter in the universe has grown and clumped together it's formed a whole distribution of clumps in the universe we can infer that and we know what it looks like and basically that's what that spectrum is that comes down there then when you drop Matic when the matter in the universe the gas in the universe the baryons as we call them they will then fall into these potential Wells of the clumps of dark matter and if they can call and form Stars we then call them galaxies and so we would expect all galaxies to have the spectrum that looks like this if that's all there was to Galaxy formation instead of which we see something looking like the points like this there are very few very massive galaxies that's rather weird but we now think that's due to active Galactic nuclei black holes at the centers of these Galaxies have blown most of the gas out back out of the Galaxy and stop them making so many stars because this is really the mass of stars in galaxies and similarly at low masses it's we think it's simply nobody blew it out so there's what is known as feedback taking place where black holes at the center are feeding energy and momentum back out into the galaxies which is affecting uh the masses of those galaxies the elliptical galaxies in the universe are now red and dead the spiral galaxies are full of blue arms and stars like that they're young stars that are forming but evidence that things are blown away from galaxies into the galaxies by um in particular winds from the nucleus is this is a quasar that's relatively near to us mercarian between 31 and somebody's gone and looked in detail with at the Spectra of gas around the center of that nucleus and compared to the velocity of the Stars which are not shown at all in this image of this representation we see that the all of these points have got negative velocities some of them very large thousands well over a thousand kilometers per second before the gas this is a measurement of the gas near the center of the Galaxy and basically it's coming out of the very high velocity velocity is at a thousand kilometers per second are very difficult to sustain due to Stellar processes in a galaxy another process which is important and it's the one I've been working on quite a lot is radiation pressure now this is Comet hail Bop shown just in projection near the Andromeda galaxy but I like it because it's of this coincidence that it's got two tails and the tail I'm interested in is this one the dust tail and the sun happens to be over on the left you can't see it in this image and basically the dust tail is caused by radiation pressure from the sun which pushes the dust from the comet out away from it forming this wonderful tail the iron tail is caused by the wind from the Sun the solar wind and picking up ions in the comet and taking them out as well so a lot of this the radiation pressure and winds uh push gas out and that's probably what's happening in these active galaxies now this is just showing your schematic in work I did with Roberto mayolino and we ended up with this press release press release of a paper we had in nature where we had predicted there would be star formation in these outflows and indeed that's what we saw so this is you've got to get the picture that the enormous amounts of energy from the Jets Jets like this and winds and radiation pressure pushes and forces much of the rest of the gas and the Galaxy out and away so we change the map the potential for more stars to form in the Galaxy it truncates the star information and the Galaxy when we get all this activity and also because we could maybe in form stars in the outflow at the same time we can change the shape of the Galaxy so all of these things are quite profound in terms of how the whole thing will work and I just walked up go a little further with looking at let's just look at this image which is a Chandra Observatory image of the center of the Perseus cluster of galaxies it's an image I had a lot to do with and what we see there is that nucleus the active nucleus of this object is there I'm not going to talk about all the details but much of this inner structure which is on a scale bigger than that of our galaxy let's cause these holes in the emission and those holes and these are essentially bubbles bubbles in the surrounding hot gas and this bubble here is much bigger than the size of a whole of our galaxy and that's all being produced by energy coming out of the active Galaxy that the black hole at the center if you compare the size of the Event Horizon of that black hole to the size of this region we're looking at so I can't possibly draw the size of the black hole layers out of the size compared to this size and the ratio is about a billion okay and it's comparable the effect of a black hole on its host Galaxy is rather like thinking of something the size of an orange affecting the evolution of the Earth that's what these black holes are doing the supermassive black holes are controlling the galaxies they live in that's radio emission I want to end just by talking about merging black holes and another Nobel Prize this is just an image of imagine that you've got two black holes in the sky and gravitational light bending has distorted the background style things that's how you can tell the black holes are there and these black holes are orbiting each other and let massive black holes are going to orbit each other and in about five billion years our the black hole at the center of our galaxy is going to merge with that of the Andromeda galaxy because that has actually is coming towards us but this is really made for Stellar Mass black holes where it's a black hole of say a 30 solar masses and 50 solar masses merging together and something like that's a computer simulation but this was actually observed with the ligo instrument where there are two executive instruments one in Hanford Washington and one in Livingston Louisiana and they shot that in when they switch this instrumental in September 2015 they saw this chirp of the the it's the strain now they they were interferometers having this time into parameters like the ones you have in a physics lab where you're measuring the length of something and it's two arms perpendicular to each other and what they arms are being that their length is being oscillated by a gravitational wave passing through these instruments and the gravitational wave is coming from a very distant Galaxy and you can see that the frequency The Strain is going up and the frequency is going up at the end and all of this fits what is expected for a gravitational wave passing through the instrument gravitational waves were first predicted by Einstein in 2016 and they were discovered here in uh 2015 and uh wise um and uh buried and um keeps on got the Nobel Prize in 2017 for discovering it I just got I've got a couple of slides I just want to finish with and this has got equations on I know you're going to say oh equations yes well I hope some of you like equations you can do this yourself on the back of an envelope I want to just ask what is the maximum power or Luminosity you can get from Mass m Now power is energy and we call it luminosity and that is energy divided by time I want to get maximum the energy is MC squared and I want to get the it out on the shortest time and from causality because I want one side of it to know about the other the shortest time is going to be R over C so I divide them and I get m c cubed over r so I've got to make it as small as possible to make the time as short as possible I'm going to release the energy how small can I make it I can make it the size of a black hole GM over C Square that's for a spinning black hole so they're going to make the very smallest black hole when I do that the M cancels and I'm left with C to the fifth over G I'm sure all of you know that c is a very large number that's the speed of light to the fifth power is a very very large number and G is a very small number so C to the fifth of over G is actually a very large number the maximum power is 4 times 10 to the 52 Watts and you notice that last canceled out of this that's because the power only lasts for a time which is R over C okay so which print low mass object can be very very short but the maximum power is 10 to the 26 solar luminosities 10 to the 26 solar neuroblastes so we can put it on this diagram which is power or Luminosity versus Mass and here's the mass of the universe about at least a variable content of the universe is is here and that's there's a 100 million 10 to 11 stars in the galaxies 2011 galaxies in the universe that's all all the stars in the universe 10 to the 22 solar luminosis and it turns out this gravitational wave was more luminous than that so just briefly the production of that flash of gamma of gravitational radiation which is coming from the other side of the universe equaled the radiation out of all the stars in the universe and this the rest of this plot you could look at some other time it's got quasars AGN and so forth aren't that one can think about power in the universe but I I think it interesting to realize that black holes can produce the highest levels of power in the universe so there's much more we could say about black holes but they're certainly here to stay but Astro visible black holes are playing a very large part in shaping galaxies and telling us and infecting how uh they act and evolve I'll stop there thank you uh you mentioned the angle of image captured by EHT of m87 platform so is it solid angle no it's it's a Well the 50 uh micro up seconds is is purely you know a regular angle and that is the radius of this ring that you can see so the next one is uh why time slows around massive objects at high velocities and stops at Event Horizon of a black hole well it turns out that time as you know if you know anything about relativity special relativity if you move moving clocks run slower and things like this and essentially uh what has happened is the effects of the black hole is to completely wrap space-time up that's the best way I can put it to cloak the black hole um with space time which is wrapped up into this uh with this event horizon which in the case uh an object of one so that's is a radius of uh three kilometers so uh what this means is that in order to do this you need a lot of matter in a very small radius and just to say it here's my hand and if I was have a black holes that I could put in my the cup of my hand it would have a mass that is about 10 times the mass of the Earth so we're talking about very compact things but if we could do that then basically as you approach The Event Horizon um it then as seen by an outside Observer um then time appears to slow down now if I may just say that if we go the other way in terms of masks if we go up to these 10 billion solar mass black holes then the size of their event Horizons is the size of our solar system and if you fell into one of those it would take you a week to fall to the center and as you fall through the Event Horizon you would not notice anything okay and actually the mean density of such black holes is less than the density of air however as you fall closer and closer into the center then the rest of the universe would do its it would appear to speed up to you but you're also falling in so that that's stop-ups so you're seeing the end of the universe but essentially you would fall in until you reach the spaghettification level where your feet accelerate away from your head so the next one is uh if speed of light slows down in different mediums though gravitational waves slows down to one different medians a good question I I guess so but um basically um I mean gravitational waves that we see um I I doubt you could to actually detect anything like that and I'm more of an observer than the therapist um I think we don't have enough matter uh to to be able to make any experiments that could test that but as far as We Know the um gravitation yeah it it it travels at the speed of light and would um I I guess there would be such effects of has there been any Observer evidence supporting the theory of radiation not yet um that Stephen Hawking did an immense uh amount of very important work on the theory of black holes on theoretical black holes and um many of you will know if you've read his work uh that he predicted that black holes could evaporate due to the emotion of walking radiation um actually in terms of astrophysical black holes um then the level of energy that comes out to the Hawking radiation is Tiny okay so if we were to look at one of these simple massive black holes then the energy that comes out in the lifetime of the universe in Hawking radiation is less than the energy of one Optical Photon it's only from very small black holes that you expect to see uh Hawking radiation like small black holes I mean ones of masses much less than the mass of the Earth and and we don't know of any such black holes it doesn't mean say they can't exist but we we can think of no way to form them other than in the primordial Big Bang and uh there's currently no evidence that uh such black holes form during the Big Bang but who knows uh maybe somebody will discover such objects in the future okay sir uh so the next one is what actually Rob space and time mean if possible can you please explain it in an easy language [Laughter] if you go in and look at look through a glass look at look through um lenses and so forth what you're doing is uh warping our appearance of space that I don't know how to walk the appearance of time I'm afraid you know maybe you can drink something but that's that would be personal to you um the the but the effect on time gravity effect on time is as I say it's something we live with in terms of if you have a Sat Nav it has the correction for that it it's difficult to think of other ways in which it can be observed but it just means that basically time is being completely distorted it's not something absolute there's not a rigid framework somewhere of space and time which is rigid it's affected by the presence of matter matter you know changes and affects space-time and actually space-time effects the way that Mata behaves there's a sort of symbiosis there what is it uh the next one is the Ken to neighboring black holes spinning in opposite direction repair each other I don't think that they could repel each other it's an interesting question but certainly people have done lots of studies of merging a black holes including spinning black holes and ones that are spinning opposite to each other so rather than going around together they're going against each other at such uh simulations show interesting features but they don't show them being repelled the one interesting thing just in terms of repulsion okay I just want to mention is if you have two black holes which come together and merge where they finally merge they merge at a particular angle okay and if you think about it you know that's something a little odd they have to it's something to do with the initial conditions but they they merge along a particular angle okay and that means because they're sending out gravitational waves and gravitational waves carry momentum so there's a problem about momentum okay and this can lead to a recoil of the collapsed object so the black holes come together a merge to form an object and depending upon the spin of those objects Etc so it can shoot off and you could get an example where the the resulting black hole has a velocity of hundreds of kilometers per second and is ejected from the Galaxy I mean people have started to look for such things but that there are interesting things to do with how it goes okay and if they could just say one thing about the black hole merger that is is amusing to do is um get a dinner plate um don't get your um partner or mother or grandmother's best dinner plate but it gets an old plate um and you know so you've got the plate and put it on a table and spin it so it's going around you know like that okay so it spins Round And as it if you do it carefully you can get it spinning for quite a long while but eventually it'll start spinning and it will you know go flat and in the final part of it it actually the way in which the frequency with which it spins together makes something which is uh and it follows the chirp that I showed you in that merger of the black holes it's it's a very similar development where it goes faster and faster and the frequency is going higher and higher and the volume goes up so that's a do-it-yourself experiment which is um telling you something a little bit about physics and how things can collapse uh so the next one is uh last gravitational field went like so there must exist a specific path through which the light moves and return back to its starting position just like Einstein thought experiment it can allow time travel can you please comment on this um I don't know that we can actually I mean you can get like to set up turn back on itself yes on but uh I don't see how you can actually get um couple that into time travel and I I I'm just getting put in my neck out now I don't think time travel is possible okay okay but the only way to be proposed to do so is if you get something called a wormhole and you'd fall into that and it has to be in a spinning black hole where the singularity is actually not a point it's a ring and it falls through the ring um I think you'll be killed in doing that but um what you do is you'll end up in another universe so it that is if there are other universes and I don't even know about that but um I I personally um yeah actually most of us love to love to watch start Rex and Star Wars and so yeah so the next one is uh uh the spiral shape of Milky Way is a consequence of presence of Blackpool cause the spiral shape the spiral shape I think is because we've got the galaxies it is a disc shade and it's it's the spiral is uh caused by interactions within stars and it's a self-gravity of the material in the disc in other words parts of the disc being at gravitationally attracted to others it creates an instability that leads to spiral arms where the angular momentum from our galaxy came from in the first place it's probably due to Tidal talks with other lumps of matter earlier in the universe uh so the next one is why are super massive black holes always located at the center of galaxies it's in the same way that if you if you have a search of that uh a bow with water in and you put mud and stones in very quickly the the um Stones go from the go to the bottom and we'll go to the middle of the bottle and and the mud particles will float around and take a you know if you leave it long enough the mud will settle out as well but if you Swirl It round give it a bit of rotation then they probably won't um so it's because they're much the black holes are much more massive than the stars and so they move relatively to the stars that the black holes will move through a star field and they will perturb it and they actually will through gravitational perturbations they will transfer some of their energy to the stars and that will cause it them to fall into the center but that's how it works he said I'll take the last three to four questions now well the first one is the matter dad get lost in blackpools so is it possible that a reverse Higgs field is generated inside a black hole that takes away the Mass from the particles just as Higgs fiend provides vast to all particles sorry I have no idea also like resist um and uh so yeah sorry I can't answer that one focus it uh let me ask you the next question what will happen and if the sun turns into a black hole the sun will not to turn into a black hole okay it will end its life as a white dwarf it will collapse to an object the size of the Earth if however due to some unknown process the sun was suddenly to convert to a black hole we could continue to orbit it and uh roughly at the same radius if there was no matte slots I I you know I don't know how this process would work but um basically we would continue to orbit it so black the idea that black holes suck everything in is actually a false idea and you need friction to cause them to to cause a matter to sink inwards and that requires collisions and or magnetic fields foreign of Stellar Mass black holes by fitting the Continuum x-ray Spectrum we um the what the work that I do we use the RMK line there's another approach which is using the Continuum measurements when they're in the so-called soft State when you're measuring the emission from the hot accretion disk when they're in a particular state that there's very fine work being done on that um by the late Jeff McClintock on others and they often come up with answers which are very similar to ions um on the same objects if we actually happen to have them so these are just two ways of uh measuring the properties and measuring spin of the black hole foreign is it possible to have more than one black hole in a galaxy um yes she can it has been a badger you could end up with two black holes at the center um and you know it it takes a long time for them to merge together I sort of rather implied the Andromeda in our galaxy the black holes would merge very quickly but that doesn't happen very quickly so you can have uh two um and people are looking for such objects and um when those mergers occur then um we can actually measure the gravitational waves from them if we have instruments capable of doing so um the ligo instrument and by the way there is a light ligo India India is going to have a ligo project um I I hope up and running by 2025 but um to measure mergers of Black Max supermassive black holes you need to have uh to be able to operate at much lower frequencies which you can't on the surface of the Earth so you need to go into space and Lisa uh sorry um Issa the European Space Agency as I planned a mission in the 2030s called Lisa which will measure such such things and mergers a binary black holes is one of the top things to do thank you Professor Fabian for such comprehensive explanations thank you so much thank you thank you very much Professor Praveen uh any concluding remarks from your side and then I'll close the session thanking for the opportunity to talk to a large number of students and others in in India I enjoy my time when I come to India and uh you've got an exciting future as we heard in in astronomy in India I hope whatever you do you support that work and at the same time let's try and propagate the scientific method that's important to do particularly when there are pandemics around thanks for watching please subscribe and don't miss out on new videos and lectures thank you