Black Holes: The End of Time or a New Beginning?

good evening everyone my name is andrew frak noi i'm the astronomy instructor here at foothill college in Silicon Valley and it's a great pleasure for me to welcome everyone in the auditorium and everyone listening or viewing on the web to this special lecture in the 13th annual Silicon Valley astronomy lecture series these lectures are co-sponsored by 4 excellent organizations the NASA's Ames Research Center the Foothill College astronomy program the Astronomical Society of the Pacific and the SETI or the search for extraterrestrial intelligence Institute and we appreciate their help in bringing speakers and doing publicity for this lecture program I'm delighted to say that tonight our speaker is one of the most distinguished astronomers in the United States dr. Roger Blandford dr. Blandford a native of England took his degrees at Cambridge University where he was supervised by the astronomer royal Martin Rees he joined the faculty at Caltech in 1976 and was appointed the Richard chase Tolman professor of theoretical astrophysics distinguished named chair in 1989 in 2003 dr. Blandford moved to Stanford University to become the first director of the Kavli Institute for particle astrophysics and cosmology at Stanford he is also the Luke blossom chair in the School of Humanities and science he divides his time between the physics department and the Stanford Linear Accelerator Center which is a national particle accelerator laboratory his research interests include some of the strangest things going on in the universe black holes the origin of the universe gravitational lenses cosmic ray physics and compact stars among the many international recognitions that he has received for his work he has won the Eddington medal of the Royal Astronomical Society and the humbled Prize it's for me both a personal pleasure and a professional privilege to introduce to you talking about black holes the end of time or a new beginning dr. Roger Blanchard black holes have a very bad popular image they are seen as agents of death and destruction as torturers and annihilators have been several movies made about black holes here are two where the black hole casually ended the careers of several promising neutral movie stars having countless novels here the casualty was the english-language black holes have inspired some of the most confusing scientific illustrations I have encountered and some of the lamest cartoons I'm entering the black hole now would grief it's full of unmatched socks there's a career here for all of you young people you can't do worse here is a better book written by the late Carl Sagan which is made into a famous movie as is common in this genre the plot became so torturous that the only way the scriptwriter could escape was to invoke a variant on a black hole called a wormhole this would allow you to pass from one place and time to something quite different sounds like a good idea but the reality of wormholes is quite contentious if you ever come across a black hole as a physicist I would not recommend the experiment here's an even better book from dandy allegory abandon hope all ye who enter here it looks like a black hole to me black holes have been feared as threats public safety it was claimed that the large particle accelerators like this one in Switzerland would create black holes and swallow the earth of course this has not happened and we knew that it would not happen because nature before was far more dangerous experiments over the time not the European debt crisis you can see people worry a lot about black holes in short they are thought to be bad now I'm delighted to be here at Foothill College as part of the Silicon Valley astronomy lectures to try to redeem black holes persuade you that they are good and that they play a an important part in the essential role in the life of the universe I would also like to try and explain to you why physicists and astronomers like myself find them fascinating it's time for me to start telling you a little bit about black holes and for that I must begin with gravity this here is Woolsthorpe Manor in Lincolnshire in England it's where Isaac Newton was born where he formulated his law of gravity those of you who know about mathematics may notice the integral signs he carved in the wall that's actually a cruel joke because Newton's great rival light-minutes introduced the integral side at Isaac Newton this is the house where he closed the walls Thor is where I was born I boast about this to my students they are quite unimpressed what's that got to do with anything a common rural myth is that mutant watched an Apple fall from a tree and realize that the fall of the Apple would be described by the same agency as the orbit of the moon and he invoked an invisible gravitational force to do the job so here in the language of mathematics is the force which you give the symbol AB and it relates it to the acceleration and the famous inverse square law of gravity these these equations are the foundation of most of the physics we know about until quantum theory came along now jump forward 250 years to 1915 Albert Einstein formulates his general theory of relativity he combines three-dimensional space and time into a single entity which he called space-time he discovers that space-time is curved when there is matter around in addition he does away with Newton's invisible force and describes the motion of the Apple and the moon as a straight line in a curved space-time here is Einstein's equation it looks very different from Newton's law but the outcome is actually very similar and the small difference is from mutants description are today measured accurately Einstein's theory appears to be correct about to about ten parts per million we have no grounds for depth doubting it as far as it can be used within a year of Einstein's formulation of his version of gravity a German soldier Karl swats Jill also happened to be professor of astronomy discovered a strange solution for the equation that I just showed you today we know that it describes a black hole it was a special spherical surface the describe that surrounded this black hole which we now call the event horizon and for which nothing neither you nor I nor even light in this game this is the point of no return they say the event horizon here's a black hole and surrounding it and graphically here is this surface this black this event horizon that the light cannot escape from the black hole itself has mass just like the Sun and the bigger the mass the bigger the event horizon now what this show what Karl Schwarzschild here showed was that mathematically black holes can exist at the end by the end of the 1920s it became clear that the type of star known as a white dwarf star was supported by the same sort of electron pressure that we find in metals a young student I shown here some super ammonia and Chandrasekhar and others realised that these white dwarf stars had a maximum mass about one and a half times that of the Sun and this white dwarf would have a size about that of the earth if the star became more massive than this the electron pressure would be inadequate to impose gravity moving forward in the 1930s like now a Russian scientist and the local scientist K Robert Oppenheimer and others considered another type of compact star called a neutron star and here the maximum mass is about two and a half times that of the Sun we know that these stars can exist because we see thousands of them around us as they speak however when as commonly happened as compact stars have more than two-and-a-half solar masses two and a half times the mass of the Sun they must collapse the form of black hole in other words black holes must exist that's what the astronomers tell us actually there is a complication here and this caused much confusion if we were to watch a star collapse the form of black hole it would take formerly an infinite time so many scientists said the black holes should never fall the fallacy in this interpretation was exposed by this American scientist John Wheeler and his colleagues who said that if you were a fortune enough to sit on the surface of a collapsing star was about to make a black hole the black hole would as far as you were concerned form in a finite time less than a millisecond for a star for a black hole of of a massive bat few times that of the Sun say furthermore the collapse will continue until gravity but stronger and stronger and the laws of physics that we understand would break down this anarchic state this end of time is called a singularity it was much more that was understood around this time in the 1960s by Roy Kerr and New Zealand Earth Roger Penrose an Englishman and Stephen Hawking so they got superposed the graphics there Stephen Hawking also an Englishman what they discovered they in their colleagues was that black holes are really very very simple they are all surrounded by event horizons and the ones that show up in astronomy are described by their mass and their rate of rotation no more no less we also learn how to do regular physics around a black hole so to summarise asked if as a physical black holes are characterized solely by their mass and how fast they are rotating how fast they are spinning they trap light and they they black holes these black holes cannot be escaped there's so much for theory let's allow the astronomers pick up the story recall that I said compact stars larger than two and a half solar masses must be black holes in the 1960s astronomers started to be able to observe the sky not just using optical telescopes or radio telescopes but using x-ray telescopes here is a modern one the Chandra x-ray Observatory makes exquisite images of x-ray sources in the sky and is named as you might guess after Chandrasekhar whose picture I just showed you in the previous slide the x-ray astronomers found many new sources and in 1971 they found one in particular shown schematically here the imaging of x-ray telescopes is not that good so this goes as a picture here it's called Cygnus x1 Cygnus x1 was actually two stars if you like in orbit about each other a binary star one of them was just a regular star and the other one was a compact star might have been a white dwarf it might have been a neutron star but it was weighed it was possible to use the dynamics of Isaac Newton weigh it and it came in heavier than two and a half solar masses therefore it was a black hole black holes therefore do exist you might be wondering why these black holes are observed in this way after entering their stellar careers as lifeless corpses why should they be reborn as x-ray sources the answer is depicted here what happens is that the star grows in size the star here as it gets older it gets a little bit bigger sound familiar the star grows in size and the gas spills over to make of discs the twirls around the black hole this disk is known as an accretion disk and friction in the in this accretion disk causes the black hole to get hotter and hotter as energy is released in fact you get so hot that emits x-rays now these black holes and their accretion disks are extremely efficient gravity power is shown here this gas spiraling inward through that disk into the black hole or it crosses the event horizon it will be a hundred times more efficient the nuclear power and nearly a billion times more efficient than dynamite so if the world wants to solve its energy problems all we have to do is catch a black hole however please do be careful now there's a second feature of black holes being supplied with gas in this way that you can see depicted here and I'll have more to say about this this is a jet these black holes not only have the gas going in they make streams of gas too in opposite directions here flowing out at very high speed most of the speed of light by commonly these are called Jets this is gravity power now black holes and there this have many other strange properties one of these is that they can sing they can in fact what's happening is they're oscillating with frequencies and the fact that kilohertz range that you can listen to as you don't hear sound waves crossing interstellar space but you can transfer the electromagnetic signals that you get into a noise that you get is what it sounds like this is one of like holy sounds like I think it's musical well I am tone-deaf there are many theories of how the black hole performs this trick how it oscillates regulate a bit like a clock like it's a bad clock I'll add a shortly add another one to this like holes can also dance here is another famous source it has the rather forgettable name of SS 433 again there's a star and an accretion disk and two Jets the pair of Jets may gas streams out in the opposite direction we're almost exactly a quarter the speed of light and what happens is that they fire all around these two Jets so if you imagine that's a black hole that's an easy enough thing to remember and here are the two Jets then they spiral around life after procession they do this in the back half a year every half year they spiral around and astronomers can watch them spiraling around like that it's a bit like having a hose pipe and swirling it around they make these sort of curving patterns you can see it here here you can see the observations in x-rays you receive the swirling happy hair remember this because I'll come back to this a little bit later there's a black hole there this is swirling partners you sort of two-lap DiPaolo x-rays you swirl around now this is the powder dough this is a dance of a black hole and it's got tiny under stars so black holes are not just insatiable gluttons parasites on cosmic society they actually give something back in particular there are supernova explosions which involved in the formation of black holes and gamma-ray bursts which are very energetic they create I think I put a slide out of order here let's just go to the next one and I'll come back to that one if you're prepared to accept black holes in a metaphorical sense is alive not dead how are they born or reborn it turns out that there are two ways that we are probably seeing black holes being born the first involves special neutron stars called pulsars here we see two pulsar is depicted and these special pulsars let's shift so two neutron stars there and what makes them pulsars is they make two beams of radio emission like cosmic lighthouses and when they're close together they will all with each other and we know several examples of these and we can weigh them now what happens with these two neutron stars is they spiral around each other like that and around and then they radiate what's called gravitational waves and these orbits get smaller and smaller they sort of shrink the orbits and then eventually you've got these two neutron stars they one-and-a-half solar masses each and they combine into a single object one and a half plus one and a half equals three three is more than two and a half therefore they make a black hole so black holes systems like this in a hundred million years are bound to make black holes so not only can we say the black hole is doing we can also say they will exist there's a second way of forming them and that is to supernova explosions these are involved the massive stars who have lived fast and died young the run out of gas they have collapsed under the unforgiving pull of gravity they have released energy and exploded as these supernova explosions here is a very famous one that happened in the nearby galaxy called the Magellanic Clouds it blew up in 1987 and people were able to see it easily with their naked eye and and the black hole was almost certainly formed in this system the center cannot hold mere anarchy was loosed upon the world as it said so we see supernovae across the universe we see them back to the early stage of the universe and they that they can outshine galaxies for a few months usually they leave behind black holes occasionally they leave behind just shows to me usually they leave behind neutron stars occasionally they will leave behind black holes and this is a second way of forming black holes in the supernova explosions now what is remarkable is that these two ways of making black holes also do something else it appears that they also create bright flashes a very high-energy x-rays which we call gamma rays and these objects are seen these birthing black holes are seen as what we call gamma-ray bursts and the gamma-ray bursts can also be seen across the universe for us every day a gamma-ray telescope we'll be able to detect a new Gabourey burst it makes a bright flash of gamma-rays we see it for a few seconds in the case of in this case here with the tube what we think of the two neutron stars it is slightly less than a second in this case here it takes several seconds to be over but in both cases we see these bright flashes of gamma rays and they are called gamma-ray bursts so these are if you like the birth cries of black holes who did try and give back this is the slide sorry to go out of order so I said the black holes were just insatiable gluttons they're parasites on cosmic society and they're giving something back the super novae and the gamma ray burst explosions are very energetic they create a blast that explains out to hundreds of light-years these are the remnants of supernova explosions that happened over the past millennia in fact they were observed as many cases observed as supernova explosions and the dates are known when they happened these explosions do three very important things firstly they create heavy elements like carbon and oxygen and nitrogen and iron these are the ingredients of life they also disperse these elements into the space between the stars perhaps ultimately allowing life at least in its most primitive microbial form to propagate secondly these supernova explosions caused other stars to form and perhaps make their own planetary systems and finally these supernovae and therein remnants which we see shown observed here they make very high-energy particles called cosmic rays as if are a terrestrial life is concerned they help bring about the mutations and the evolution we have witnessed on this earth though my contention is in spite of all the bad press they get black holes are ultimately very good for us too this one the black hole that I've discussed so far I'm not much more massive than the Sun there is another type a second type of black hole that astronomers commonly observed and these are called massive black holes and it turns out that essentially every normal galaxy as an it's center right in its very center a massive black hole just like every atom has a tiny nucleus at its center our galaxy is no exception it has a 4 million I peak that 4 million solar mass black hole they and we know if it's 4 million solar masses it's because astronomers like my colleague Andrea guess at UCLA can actually observe the motion of stars going around them just like Kepler could observe the motion of planets going around the Sun and you can use Newton's law again to measure the measure the mass of the black holes what we have here are the orbits this is not just the orbit that happened today this is actually the orbits projected with great confidence until the middle of the next century but we've seen enough of these orbits to be able to measure them and infer the mass of the black hole but the black hole itself is very small perhaps 10 times the size of the Sun we know it is small we have evidence of this small because we see for us looking small but also at various it bear is very fast in fact in a quarter of an hour that emission that you get clicking the infrared coming from very close to the black hole is varying significantly it's changing on timescales of quarter an hour that says it must be very very small that confirmed that confirms the idea that there's a black hole where four million solar masses here's another galaxy one quite close to us actually it has the name Centaurus a this has a black hole that's nearly a billion solar masses not a million but nearly a billion solar masses here it is seen we got Hubble Space Telescope right in the center so there's a black hole there and then there's a jet you see a jet coming out of the black hole in the center of the galaxy in this case we see the jet using x-ray x-rays we can also actually see it in gamma rays on the very largest scale it's quite remarkable so what we have is something very similar to what we found with the black holes with stellar companions with star companions there's a disc of gas in the middle of the galaxy we observe it in the infrared and it creates a pair of jets which inflate two large giant bubbles see down here now where does the gas come from it doesn't just come from one star comes from all of the gas in the galaxy that's pulled in by the gravitational force of the black hole sitting in the middle remember this is nearly a billion solar masses where it is very very small here's another third galaxy that I'll show you it's a bit further wave and Centaurus a it's known as m87 or perhaps more romantically as virgo a it was discovered by Heber Curtis working close by at the Lick Observatory on Mount Hamilton observed here this isn't his image of course but he observed with something you can see in here about what he called a curious great ray apparently connected with the center or nucleus of this galaxy by a thin line of matter this was in fact the first observation of a jet which I've already introduced today we know that m87 is a giant elliptical galaxy in the center of a cluster of galaxies and the nucleus of this galaxy contains a six billion or six or seven billion a quite sure which heads back can't quite resolve that solar mass black hole and the straight rays I say is a jet so let me show you some more images of this there's a an image made with Hubble Space Telescope there's an image made with Chandra Observatory which I told you about there's an image made with a radio telescope it's the same jet seen throughout with different types of astronomy using different types of electromagnetic wave there's a close-up of the radio and down here is what until recently about five years ago with a spectacular tour the force of radio astronomers using a technique called very long baseline interferometry using this technique they will make able to see down close to the size of this black hole at a hundred times the size of this black holes a an image which is depicted actually make an image which is depicted here using a radio telescope and you can see on this very small scale you see the Jets are still being formed so the Jets that form we actually could observe them down to about a hundred times the size of the black hole and they were still there so it's a phenomenon intimately related with the black hole now what I have to tell you is this in the last but a few weeks ago it was announced that you are able to see structure on even smaller scales in these in these in this source and you could now see down into about five times size of a black hole so this is a remarkable technical tour the force we're looking down we aren't able to make an image yet on that scale but that will come before too long this is really quite remarkable it's like being able to see atoms with an atomic force microscope which some of you may know about let me say a little bit more about these massive black holes I said seven billion remember the black hole in the galactic center was four million this black hole in m87 was seven billion but it is not the champion work for my colleague trump amar at berkeley has found the current champion and that is argued to be weighing a twenty billion solar masses twenty billion that's heavy is a sorry this is this is the Subaru telescope on Mauna Kea in Hawaii it's a Japanese telescope and one of the things that they have found is that they are able to find very massive black holes very early in the universe and so big black holes exist when they themselves were very young when the universe was instead of 14 billion years old as it is today was only 1 billion years old so there's a bit of an EBT academic and doctors have shown that older black holes are obese because they ate too much when they were young so remember that all of you under 18 year olds here making too much noise now I said we are feeding these black holes we feed them their food that they like it's mostly hydrogen gas probably not very appetizing to you or to me it swirls around the black hole in the disk and makes Jets just like we saw with the smaller black holes here's a special case when you really feed this black hole very well you give it all the food it could we wish for in that case it makes an object called the quasar and here's the very first one that was discovered in 1963 by my colleague Martin Schmidt in 1963 and what you see here is a star-like object which turned out to be the nucleus of a galaxy and coming out of it as a jet and right in the center of this is a black hole and what was special about this discovery was that the emission the radiation from this black hole was so luminous that he dived Shawn completely out Shawn all the stars surrounding it all the hundred billion stars surrounding this black hole in the galaxy that was around it are out Shawn by just the tiny black hole being fed with gas no bigger than our solar system right in the center of this black hole and that was most of the path that was made by this galaxy this discovery remarkable and we now know thousands and thousands of these quasars and they radiate powerfully and they do so because there's a black hole there and it is supplied at a prodigious rate with gas I said that there were jets the hero here are several of them here is a radio image of a galaxy here by galaxy with a black hole in the middle of it is a jet coming out of it jet is so powerful so relativistic it goes way outside the galaxies we look at it on smaller scales we see there's a jet and we look on a smaller scale as a jet there's a jet like one of those Russian vitru scar dollars you keep on taking it apart and there's a jet and as we've seen if you go down to a size not much bigger than the black hole there is still a jet here's the most famous of these Jets associated with galaxies it is called Cygnus aids for the first of these big rates is a radio image the first of a big radio images that was discovered associated with extra tactic sources and there's the black hole of the middle of a galaxy there and the jet coming out and inflating these two giant bubbles on either side of the galaxy these jets that are formed can be impressively straight here's an x-ray image of one here is a black hole in the middle of a galaxy called Victor ray and here's the x-ray image you can see it's dead straight that is true to a physicist that is a truly remarkable phenomena in order to be unstable it ought to be dancing whirling around all over the place and yet nature seems to make it very straight that is a real puzzle but that it isn't straight sometimes you get this host by defect in this case there are two galaxy's in orbit about each other in this case there are two Jets coming out of two black holes into galaxies about each other this case is one this sort of SS 4-3-3 type processions going on though there can be lots of dancing going around with these massive black holes as well as with the stellar black holes now when I talked about the theory of black holes I emphasized that the Astrophysical ones were characterized by two quantities a mass is it big or small and then a spin is it spinning as fast as it can or just a little bit slowly just turning a little bit slowly this second quantity called spin was a bit of an enigma to the observers until fairly recently because it wasn't quite clear how to measure it black holes are featureless their services have no marks on them if I look at the spinning earth or spinning top or something I can tell how fast it's spinning because it's usually some mark on it to show it black hole surfaces these event horizons are smooth there is no feature there and so we have to use indirect arguments to find out how fast they are spinning one of them that can be used this is a Japanese x-ray telescope that first did this Drake was to look at the emission from iron atoms in the accretion disk surrounding the black hole and the iron atoms if they were just sitting at rest would emit a spectral line with a certain x-ray frequency or energy you just get one spectral frequency or energy but if they're swirling around the black hole there's a Doppler effect that works and that Doppler effect means that the atoms that are coming for eyes that are coming towards you I'll have a little bit the photons that they emit are a little bit more energetic they have higher frequencies greater energies and so on and the ones that are going away from you it's the opposite they have lower energies lower frequencies and so you if there's a lot of swirling around then you get a large range of energies the bottom line of this investigation which the end extra astronomers were able to make was that the black holes that you see in many of these galaxies not all of them but many of them are spinning very rapidly nearly as fast as they canvass we're not totally secure in that conclusion but it's certainly a strong indication from this and other lines of observational evidence this point I want to bring together these observations and this theory to discuss how is it the black holes create the Jets we have a black hole in the middle of a galaxy say we have a disc of gas that is swirling around it that disk of gas perhaps like Saturn's rings you just friction will cause the gas to move inwards and then cross the event horizon why why why did it choose so commonly to make these giant spectacular outflows these giant Jets one going up and one going down why should it do that well we think we're beginning to get an idea we think we're beginning get an answer and to do that you should turn back to the early 19 min nineteenth-century here is Michael Faraday who discovered about electromagnetic induction this was pure research and when asked what use it would be he gave two answers one was what use is a newborn child the second answer was to a politician I don't know but one day I am sure you will tax it I think that is appropriate today for those who who believe there is a benefit in basic research not just in research physique Liam Portman supplied and with immediately if you help you make money will save well so this is a an idea that he had which made into a spectacular application for too long and its associated we said with Michael Faraday's Lord a hard part of what he discovered was if you had a spinning body a conductor some metal or something like that you had some magnetic field then if it the magnetic field with countered with rotation the combination of magnetic field of rotation would create an electrical voltage and that electrical voltage is called electromagnetic induction can be measured and of course could be used to generate electricity and so on it's not quite the way it's done enough in a power station but the principles are very much the same now a black hole also behaves like a conductor it's not a perfect conductor it's enough gate it has a resistance the resistance is about a hundred ohms those of you who understand Ohm's law V equals IR this must come back as a memory to some from some high school physics course or whatever so we make a voltage and we have a resistance of about a hundred ohms and so we can calculate the current that flows in circuit and those of you who remember some more of your high school physics can take the product of the voltage and the current to get an estimate of the power and this is what we think is happening in these systems I'll show you this are our food again this is just the cartoon this is not the calculation things do it essentially what we have here is an accretion disk in green and so magnetic field lines rather like the magnetic field lines that are associated with pictures of the earth and the iron filings the round bar magnets and so on so these are the magnetic field lines and we spin these magnetic field lines because they're attached to the black hole and the accretion disk and they make a sort of magnetic sleeve time make that sort of magnetic sleeve and that magnetic sleeve he finds the jet I see I've got the colors wrong here it's normal that fields agree but in this case they seem to be red I apologize right um so applying the ideas about Michael Faraday and combining them with the general relativity about that Einstein you can make a similar type of electromagnetic inductor which makes these magnetic fields and creates this sort of magnetic sleeve that forms these giant Jets that you see and what I want to show you next is not just a cartoon but a simulation this is one that's performed by my colleague Jonathan McKinney and I think it's the most detailed calculation that's been performed today it's a full calculation using the equations of michael faraday and the equations about what Einstein then combining them in an accurate numerical computation using the largest computers available in the United States and what you can see these magnetic field lines are now in black you saw it's getting started up you see it looking from above and you can see the jet forming now in a short while we're going to change the polarity of the field we're going to make a North field into a South Bay of the South field through North field and you see what happens is the field lines have just change around but we go back and making a jet the Jets are remarkably robust but you'll also see something else you'll see that these Jets are not exactly anti parallel they're swirling up there wobbling backwards and forwards just a little bit in a regular almost periodic way why is it doing that well we've got these strong magnetic fields we've got these Jets and if we look at the accretion disk that's surrounding it we can see structure in the accretion disk and the best metaphor I could give you is something young people may not know what this is but the old people certainly well there was a craze a long time ago that was 50 years ago but hula hoops they imagined hula hoops I also brought when I suppose I'm trying to get on that do that and that is what it is like and that is the structure that is forming here and it arises naturally now remember I told you that black holes can see what that singing is a regular sort of periodic oscillation of something I promised you another theory of that and this is it that oscillation of the jet could well be the cause of the singing that we heard in those black holes so we talked about the environmental impact of the stellar black holes and their impact on life as we know it the massive black holes also have an environmental impact here is one in a nearby cluster of galaxies called the Perseus cluster there is a giant galaxy in the middle here there's about a thousand other galaxies around it we've just passed Halloween but this may look like a Halloween mask to you but in fact what we've got here are these giant red bubbles that are created by jets these are old Jets have created these bubbles and what is happening here on the scale of a galaxy rather than the scale of the few stars is that the Jets and the black holes are stopping all the gas surrounding the big galaxies they're stopping it from falling in they are preventing it from quenching the life of that galaxy from smothering that galaxies and they are creating new galaxies outside so again the black holes this time the massive black holes have a major impact on their environment they limit the galaxies growth and they promote the birth of new galaxies i've told you quite a lot about black holes in theory and in current observations i'd like to finish this lecture by telling you about what is coming what capabilities we hope to have in the near future to learn a lot more about black holes and related phenomena that we are discovering in astrophysics the first opportunity is with new radio telescopes and here are three this is the BL a very large array in the plains of st. Augustine near Socorro in New Mexico it has been a one before workhorse radio telescope the best in the world well over 20 to 30 years now and it is recently being completely refitted to make it essentially into a new telescope ten times more capable than the old one and it is starting to make new images of jets and I just thought I'd show you SS 4 3 3 again as made with the new Very Large Array telescope a second telescope is Alma in in Chile this is in the Atacama Desert and I've been there twice now and it is I think the most beautiful place I've ever seen here they're putting about 60 radio telescopes there look not at radio frequencies here but to look at much shorter wavelengths a millimeter frequencies and frequency and millimeter wavelengths excuse me and wavelengths much shorter that's more even smaller than that and by combining this telescope with other similar telescopes in other continents you can make the finest images to date of cosmic objects and in particular of black holes and we hope the using our myrrh and other telescopes like it we will soon be able to start imaging the black holes themselves seeing down to the scale of the black holes in the case of m87 or Virgo a in the case of the black hole in a galactic center they have different masses of course but the one in the galactic center is much closer and they have the same angular size and we will hope to use telescopes like this to make what's called an event horizon telescope this is a simulation but to see if this simulation is corresponds to reality that is a very very exciting prospect to actually image these drug holes here are gamma rays there is a telescope a gamma ray telescope in orbit called Fermi gamma-ray telescope after the famous Italian American physicist Enrico Fermi here's the rocket which is carried out into space this telescope which is one that has been led by my colleagues at Stanford University and it orbits the earth every 90 minutes and every two orbits every three hours it makes a an image of the whole sky by adding those images up superimposing them one after the other it has been able to map the sky in gamma rays and it is found nearly 2,000 of these Jets coming out of the black holes and galactic nuclei the massive black hole is also far much else besides it's been wonderfully successful and with learning a huge amount about the Jets and about the black holes by using observations with Fermi gamma ray to us let's go these are just mere gamma rays a laser a pocket let's go to high-energy gamma rays these are even higher energy than gamma rays which some people were high enough and here we don't have to go into space to observe these very high of these high-energy gamma rays what we can do is see the flashes of light as those gamma rays hit the Earth's a passive when they come into the Earth's atmosphere they make a sort of streak of light which you can pick up with a sensitive telescope and here's one this is in Namibia it's the Hess telescope in Namibia this is me the focus of one of those telescopes taking a picture of me taking a picture and so on this is a corresponding facility in Arizona or Veritas and using these telescopes you can look at the jets and the accretion discs associated with the black holes and you can see the bearing not just 15 minutes like in a galactic center in one or two cases on timescales as short as two minutes this is something that's more Apple with a whole get that 100 galaxies 1,000 galaxies and yet it varies on times girls in a few minutes as a truly remarkable discovery and we are scratching our heads to try and understand it so we've gone from these energetic gamma rays to the high-energy gamma rays not to be outdone let's go to very high-energy neutrinos there is a facility at the South Pole it is called Ice Cube and they try to find very high-energy particles not gamma rays which are like supercharged x-rays but you three know you may have heard of neutrinos and they can be created by processes associated with black holes and jets and they have been searching for these now several several months and they search for them firstly by looking for them because when they come through the ice beneath the surface of the South Pole they make little flashes of light so you see the lumière you can also listen to them because they make sound waves and then finally you get radio bursts with them at 2:00 as well all of these techniques have been used to search for the high-energy neutrinos and to date we haven't yet seen any so this has been rather disappointing unlike the other telescopes it means you haven't actually found anything as yet we hope we will one day but so far not now having got very high energy neutrinos let's go to the ultra-high energy cosmic rays here we have the cosmic rays which were discovered as energetic particles ah a hundred years ago this year by Victor Hess after which the namibian telescope is named here he is in his balloon going up and his cosmic ray detectors electroscopes and so on to try and discover that these cosmic rays came from outside the earth he was a very brave man he went up in the balloon he knew he would return to Earth now cosmic ray physics has advanced a lot since the days of Victor Hesse and the most exciting thing at the moment are the most energetic of the cosmic rays we have seen that ultra high-energy cosmic rays and they to make an optical flash as they hit the atmosphere it's a different type of flash but it's similar in principle and it makes this optical flash and also makes lots of particles that you could detect in tanks of water and so on but you can detect these cosmic rays and the most energetic of these cosmic rays are made by I have images comparable with the energy of a so we say a bloop single so it's a baseball hitting to the outfield I had giant appropriately enough here now if we ask what these cosmic rays these ultra-high energy cosmic rays were like when they were first created they would be a homerun that's a baseball it's a proton as that same energy out where can that come from well it has enormous energy remember I said that this is spinning black hole with a giant voltage one of the very very few places it has enough voltage to make a proton have the energy of a homerun baseball is a massive black hole in the nucleus of a galaxy it's not the only explanation but it's probably today it's one of the two best explanations left and before too long we will be able to distinguish this from the alternatives and see if it really is these massive black holes that are not only making the Jets these prodigious amounts of radiation throughout the whole electromagnetic spectrum they are also able to make these ultra high-energy cosmic rays and finally there is a hope of seeing these gravitational waves remember I said the two neutron stars firing together did so because they were emitting gravitational radiation well we can also hope to detect that gravitational radiation directly here is a facility called LIGO there in fact two of them there are one that others in other cut continents on in Louisiana the other in Washington and you look for the shaking around of mirrors tiny tiny motions of these mirrors that are created by waves are made by stellar black holes or stellar neutron stars as they merge and other sources the date this facility has not seen anything because it wasn't sensitive enough to do it but it is being retooled like the VLA and in 2015 it will start up again and he should then have the sensitivity to start measuring gravitational radiation and coalescing objects including black holes and close by stellar objects we won't see the massive black holes create these black these gravitational waves the two more techniques one is to go into space and the other is to use the false earth which I told you about which is exquisite clocks and they get shaken around to by these gravitational waves and they too may be able to make a detection of gravitational radiation a very exciting prospect a new frontier we don't know what we will discover so here are Isaac Newton and Albert Einstein they told us so much about gravity neither of them was able to explain how gravity works on the smallest scale this is the ultimate question that's posed by the absence by the existence excuse me of singularities inside black hole event horizons I hope that one day someone perhaps someone in the audience will be able to understand what it means by saying I comes to an end in the in the meantime I hope that I have persuaded you the black holes are as fascinating spectacular and good for us and they are demonstrably capable of a new beginning thank you very much indeed you'd mentioned that a black hole is characterized by a mass and spin what about electric charge excellent question the question is doesn't the black hole also have electric charge the answer is in the world of theoretical physics the answer is absolutely yes and I was very careful though to say I was discussing Astrophysical black holes and what happens is that if you put any appreciable charge on the black hole either a stellar one or a massive one then it will immediately discharge or be lightning everywhere and it just like a cumulus cloud that gets charged up it will discharge immediately so in practice Astrophysical black holes of white uncharged but the charged black hole was in fact very important the progress of theoretical physics because it opened the door to understand some very perplexing problems in theoretical particle physics by considering what happens around a charged black hole so the febrile imaginations of theoretical physicists it was very useful for astronomers less important oh there it seemed to be two microphones on it while waiting for the next question let me say here's two books I didn't recommend either and I didn't get a edit I cut on them but I recommend them to find out more about black holes and then I'm able to make unable to make available after tomorrow there's a bit embargo on some more movies like the ones that one I showed you that are actually very interesting indeed I can make those available the end of this week they'll be on my website which is shown there chillin victory over that side so I guess Oh professor pardon me my voice has a bit of laryngitis you mentioned the fact that the gallop that the black hole is a constraint on the size of galaxies but also that it promotes new galaxy formation it's curious because I understand that in the early universe some say the black holes might have been the seeds of galaxies but is there any evidence of that today that that currently black holes are promoting galaxy formation Oh so question is what happened in the early universe and the what we do know observation Lee is that black holes form surprisingly early in the universe and groove surprisingly fast as I said there were when the universe was only a billion years old it were very massive black holes already in place each Ezzor becomes a sort of chicken and egg question which came first the Galactic chickens or the black hole egg of course the authors of that is the same as leader developmental biology question is they of course they both happen together and so there's a coevolution of the black hole and the and the galaxy sorry I drew no no no no specifically is there evidence today that that process is continuing where black holes are preceding new galaxies today or within let's say the last few billion years the last billion years uh we do see structures around jets and so on that could be interpreted as dwarf galaxies in formation which may well be triggered at this late time by the effects of the black hole but most of what I'm talking about probably happened when the universe was much younger kind of just has one more is is the constraint on the size of the galaxies simply the gravity or is there something more like the mention the jet and the bubble and everything is that are there other constraints on the sizes of galaxies other than just the gravitational attraction of the black hole and I'll take my answer guys have okay so why this is a again another excellent question of why are galaxies the size they are why don't they keep on growing forever and ever one of the things that seems to be that there is a characteristic mass for a typical galaxy it's a little bit more massive than than the Milky Way galaxy but not much just a few times the mass of the Milky Way galaxy and then the it's rather not quite as many galaxies that are smaller than that and not as many as you might expect that a larger than that the reason why there may not be so many smaller galaxies is because what happens is all of these black holes information these supernova explosions and so on blow away the gas and stop the black hole from forming so there are fewer of them the reason why there may not be so many more massive galaxies is because the massive black holes and the galactic nuclei blow away the gas and the rest the even for for more gas and so it sort of switches itself off and stops more stars forming stops the galaxies from growing so that in qualitative language is what we think is going on the hexan excellent question over here friend of mine told me that um she'll say she was saying there's a black hole that is the earth and the Sun I'm afraid you go how to speak huh oh is it a black hole between the earth and the Sun and then we're going to get sucked up ah if there is I promise you will be the first to go as far as I have there can't be a very massive one because of course we know with exquisite precision the motion of planets and satellites around the solar system but if the where any appreciably sized mass orbiting there then all of the predictions of where the planet should be a satellite appears and they all be wrong and they are so fear not I think we're okay first of all great talk thank you very much my question is kind of a terminology question what's the difference between a swartz child radius and an event horizon ah okay another very good question terminology the sports child radius is the radius of the event horizon that surrounds a nun spinning black hole so this surface is service of no-return which we call the event horizon and it has a radius name I think what it's all care of and so what is radius me well what you actually do it's really quite simple you take the area of that event horizon which you can measure as a bit careful do this with this measurement but you can do this measurement okay and that area you just imagine is just like a regular sphere you say a sphere of that area what's its radius that's what you mean by the radius of the event horizon and that radius for a non spinning black hole is called the Schwarzschild radius and so now the event horizon is the actual surface if you like surrounds the black hole close the singularity I have a question about the density of black holes and it seems like they're they're sucking in matter are they primarily comprised of matter and I guess in their structure are they are they denser than a nucleus of an atom or are they like the individual subatomic particles are they like denser than a proton like they've been compressed protons and neutrons very very good question let me let me give you an answer um if you take a black hole and you say it has a certain mass which you could measure by seeing our stars go around it for example and we say it has a certain size which is the swath shield radius which we've just discussed there the last question now I've got a mass and I've got a size then I can use that as a sort of formal estimate of the density in the usual way if I perform that calculation for a massive black hole in the nucleus of a galaxy then the density that you get is the same as you or I or a bucket of water or my water here something like that that's all we are more or less the birth approximation and it's that same density more or less if I take a black hole that's all Stella like wad it's close to the density of a nuclear atomic nucleus so you see your question has a range of answers that depend on the mass of the black hole so the smaller black holes we see in astronomy are about as dense in that define in that way as an atomic nucleus and a larger one or about that bit now if you say we perform the experiment of thought experiment if you like going across the event horizon and then approaching this singularity then the density that you get as you approach that singularity is colossal it is n to the 92 or whatever it is times the density of this water it is that is why we don't know how to do physics of that scale quantum mechanics and gravity are equally important we just don't know how to have the way and so the density associated with the singularity is is enormous on unimaginable and very very hard to understand what happens at that point but if we just define the density by the event horizon the mass inside is from the size of it then it's more reasonable over that size thank you for a wonderful talk Roger one question I had do you mentioned earlier about a conundrum evokes a black hole collapsing and then I think the 60s John Wheeler oh yeah solved it if you're writing on a particle falling into a black hole you you past the event horizon in time as proper thymus is Barnard it yes from the outside I've heard the opposite black holes are called frozen stars so you actually never see it collapse but yet we see supernova explosions so I thought about it and I can't seem to cross the understanding that the paradox can you explain it a little bit more yes I think that's a very good point I'm glad you picked up on that if we have if we perform this thought experiment of somebody falling backwards into a black hole holding it holding a flashlight you know like that on me so here holding a flashlight okay like that then what you would see as a distant observer is you would see the light from my flashlight by saying it was pulsing for example the pulses would come less frequently that's what you would see they would get redder and redder and redder and then in a finite time you would see the final Photon you would never see another Photon now in some sort of silly way it would take an infinite time for me to cross the court the event horizon in your corner in your version of a coordinate system as far as I'm concerned this all happened for Estelle a whole say for example in few milliseconds you're gone so what you're seeing is just a strange way of describing the geometry of the black hole that's geared towards your particular place looking at it what will have pointed out two analyses like this that the correct way to think about it was something that really did for win a proper time and yours your viewpoint was really illusory and to all intensive services the black hole is already for thank you there was a supernova explosion of course most of the activity happens that way outside the event horizon and so it's not affected by any of these considerations questions about spinning why do they spin in the first place and how fast they spin do they have a preference for clockwise or counterclockwise spinning can we tell again very good questions of theirs what's cool rather facetiously the doctrine of original spin I think I put them on the slides and that is when the black hole forms is like you know the skater and all of that conserves angular momenta spins faster faster it's going very very fast and that's where the spin comes from that's possibly true probably true but is not the whole story it is also the case that our black holes can be spun down by creating these Jets the Jets take their energy from the spin of the black hole that's the remarkable thing the Jets take their energy spin at the black hole and they spin down the black hole to get slower and slower and slower but then as a later time when they stop having a jet they've got this gas swirling around it like Saturn's ring the gas is moving in it bringing in spin with it that spin spins up the black hole again so a typical black hole most of us believe in its lifetime over say ten billion years a black hole maybe in the stellar system but more typically in a massive the nucleus of a galaxy is going to perhaps before the spinning rapidly and then it's going to grow and slow down and make jet so there's going to be steep sped up again spin rapidly again of growing in mass all the time and he'll do this maybe ten times over its lifetime slow down spin up slow down spin up that's typically what we think will happen I don't know I understood that if if you were out in space tulips as you can see a black hole cassette set but you're showing how to test on the spinner can you sometimes see a black hole through in the midst of thes stay in the midst of it down in the midst of dust would you so repeat the question I Oh again that's what you actually see and that's why these are these graphic artists sort of headed or horribly wrong quite often there's an effect which Andrew mentioned called gravitational lensing and what that means is a ray of light gets bent when it passes through a gravitational field rather like passing through a lens now if that ray of light if the gravitational fields are is associated with a black hole then the bending is as strong as you might expect I say cats but if the ray actually goes into the black hole it crosses the event horizon it doesn't come out the other side okay and I don't not even like them escape from a black hole but I'm wondering if they if they can if they can be seen and yeah well you you can detect them you'd say can you see them the way that you would suppose you were a safe distance from a black hole and you were looking at the field of stars behind them then what you would see is a distribution of stars it was very characteristic as a sort of halo around the black hole and then something missing in the middle and that we can calculate very accurately we know what we would see if we perform that thought experiment so that's what you would actually see okay okay I understand that Stephen Hawking predicts that black holes have a temperature and slowly evaporates and that the smaller they are the faster they evaporate in that a two billion ton black hole formed and the Big Bang would be about ready to explode now can you comment anyone looking for those things oh yes I know about this in fact I was Stephens uh I had the office next to him when he was doing this work a long time ago so he was very excited about it all right it was a fantastic insight into theoretical physics that a black hole at a temperature and that temperature was actually determined by the gravity at the event horizon the black hole you find the gravity you described with your life strength of gravity of the event horizon the black hole and that is a measure of the temperature and as you correctly said the smaller the black hole the greater the temperature yes and this is a wonderful insight and he opened the door like the charge black holes to the solution otherwise puzzling problems in theoretical physics does this have any basis in observational astronomy the answer is probably not it is terribly hard to imagine how black holes could have been made in the early universe based on what we now know and didn't know in 1974 about the conditions in the early universe though most of us are highly skeptical but nonetheless astronomers have searched to what one of the things I didn't sort of follow up from this when I was much younger was to calculate what the spectrum in radio waves would be from an exploding black hole and people have looked for those using searches of red apple from radio telescopes they could even do it with the island array for example even do it with the island array and the have found nothing is yet but it would be lovely to find something for a while people thought gamma ray burst might be these but it became pretty clear that they had nothing to do with his exploding primordial black holes so my answer is probably not but I would love to be proved wrong thank you right over there yeah Marie tongue um could you say something about the status of the debate over the entropy associated with a black hole the second law of thermodynamics okay not sure it's a debate I think it's well it's some level it's a it's a closed question the associated with the temperature that there's a physical thermodynamic quantity called entropy and the scientists called jacob bekenstein had another insight that correspond with a sort of compliment of Stephen Hawking's while that the our area which I just mentioned of the event horizon I said you wouldn't define this error is the event horizon that is the entropy of a black hole at first it was just a metaphor it was just a but it's a bit like entropy and then when Stephen Hawking got his wonderful results it isn't just it's just like it isn't entropy and entropy as you know must always increase and this is the corresponding part of that is the air area of an event horizon stories increase and so what Stephen Hawking and bekenstein and others were able to conclude was the web for example we extract energy for spinning black hole to make these Jets we reduce the mass that's where the energy comes from equals MC squared that's where the energy comes from but we increase the area and we can do that with a spinning black hole we can make the mass smaller but the area keeps on increasing and that's the way we think we make those gets thank you excellent questions thank you the era of quasar is seem to be kind of like a calling card announcing the existence of black holes in the early universe any speculations as to how black holes actually did form in the early universe in the short time period right after the Big Bang yeah there are speculations and I think we're learning about that I don't think we have the full story in by any stretch of the imagination but as you can probably imagine there are two ways to make a billion solar mass black hole in the early universe alpha billion years say what is to start off with a very small black hole and keep on growing keep on beating it feeding you feeding it mini grows baby gets bigger bigger and bigger that's one way another is to have a collapse of a huge amount of gas all at once all fours are people like that okay now that second say a million solar masses of gas all clapping all together like a giant supernova explosion or burst now we see the supernova explosions associated with stellar matter they're pretty impressive objects suppose the were a million solar masses of gas that made a big black hole just like a giant supernova a million times as powerful you think an astronomer would have missed that they may be dim but they definitely may be dark at night he may be cloudy but they would not have missed that so most of us think that it doesn't happen quite that way that instead you make the black holes and rather smaller seeds they grow very rapidly but gradually not only one great week go but gradually over say a billion years and that's the way the black holes grow and they do it together with the galaxies with the surrounding galaxies and they influence each other galaxies provides them the food for the black hole the black hole provides the a blow the wind the Jets and so on the radiation that modulates and moderates the formation of stars and it's this symbiosis that probably happens in the in the formation of galaxies and the corresponding evolution in formation of black holes and the corresponding growth of galaxies and I suspect that my colleague sandy favor will say something about this when when she comes to talk to you in January okay two more questions so over there just died the Hat I've heard that black hole skin lose mass gradually through the process of Hawking radiation how is this possible nothing can escape from a black hole ah the Hawking radiation is only relevant for these tiny black holes typically they're as massive as a big mountain which is small by a stellar scale so a tiny black hole is the only time for which King radiation is asked to physically important I've argued that in fact these are terribly hard to form with no evidence that they actually exist but if we can talk about this in the point of view of pure theory and what happens is that the statement that nothing can get out of a black hole is not true in a nun spinning black hole is not true when you include quantum mechanics all of those statements were made in the context of Isaac Newton's if you like an Albert Einstein's classical physics they were not made in quantum mechanics and what you can do in quantum mechanics is you can imagine a pair of particles a pair of photons if you want one can go to the black hole the other ones hit escape you can get some radiation out of the black hole that way and so it's really the magic of quantum mechanics that allows these tiny black holes to radiate but if you have a pair of virtual particles arising in one of them falls in there's still something being added to the black hole right this yes but it can still radiate and it will lose mass it will radiate away and lose mass so yes yes it has something at it but they're virtual particles and when you do the accountancy at the end of this you end up with a balance sheet that has the black hole with less energy and less mass I didn't even answer questions are they all clockwise or counter clockwise or counter clockwise well in the normal hemisphere no they are there is no preferred direction you have to think about you looked at it upside down you know what you might think the spot voices right and so on so there's really no preferred direction of spin I think if you want to relate it to something and this is serious um a lot of these galaxies you can see they themselves as a spinning and so the question is do the black central black holes spin at the same rate as the surrounding stars and gas the galaxy you might expect that to be the case but the evidence for that is actually not strong and we suspect that they're probably not very well related this is one of the sort of very interesting questions it's associate with either the galaxy's evolved and the black holes vary with time is is the relationship between the direction of the spin of the galaxy from the spin of the black hole and that that may be what you were talking about and there the jury is still a bit out we do know something about that observation Lee but the jury is still out on that one is there very good question

Channel: SVAstronomyLectures

Views: 29,580

Rating: 4.6273293 out of 5

Keywords: Astronomy, Space, Science, Black Holes, Roger Blandford, Galaxies, Cosmology, Quasars, Time, Physics

Id: mgtJRsdKe6Q

Length: 89min 52sec (5392 seconds)

Published: Mon Mar 18 2013