Supermassive black holes: most powerful objects in the universe | Martin Gaskell | TEDxMeritAcademy

[Applause] in the year 1783 a famous British scientist called the Reverend John Mitchell the rector of this church in fawn Hill Yorkshire presented a paper to the Royal Society in London in his paper he argued that there could be in space possibly objects whose gravity was so strong that you could not escape from them even if you went as fast as the speed of light and of course if light would not escape then someone on the outside was not going to be able to see the object the Reverend Mitchell had had become the first person to postulate the existence of what we now call black holes now John Mitchell had used Isaac Newton's theory of gravity a theory which we now know is not accurate when gravity is very strong but in 1958 and a American physicist called David Finklestein used Albert Einstein's general theory of relativity a much more accurate theory of gravity to prove that black holes could indeed exist even though light can't escape from the black hole the black hole has still got gravity so it can be detected by its gravitational influence on things around it now currency dentally back in the 1780s while John Mitchell was speculating about the existence of black holes a friend of his a composer called William Herschel was using very large homemade backyard telescopes to sweep the sky and discover objects that we now recognize as being distant galaxies and in some of these in the very center we call the nucleus he detected bright points of light here's a picture of one of those ones we call it NGC 55 48 this is a Hubble Space Telescope picture of it and it turns very bright in the middle in what we call the nucleus the central galaxies there well and Herschel had no way of knowing this but he was seeing light being emitted not by stars in the galaxy there but by gas spiraling into a supermassive black hole it was not until the beginning of the 20th century that astronomers got more indications that something bizarre was happening in the nuclei of galaxies like NGC 55:48 astronomers at Lick Observatory analyzed the light coming out of nucleus of his galaxy and discovered that there was lots of hot glowing gas there and remarkably this gas was moving very quickly it was being much faster than the stars were in the galaxy in fact it was even going up to a few percent of the speed of light over the next couple of decades astronomers began to detect radio emission from galaxies such as this one here called sin a and that radio mission was very powerful in the mid-1950s the husband-wife team of Jeffrey and Margaret Burbidge calculated that the energy being put out by an active galactic nucleus in something like cen a was the equivalent of 100 million supernova explosions going off as a star exploding as a supernova it was a tremendous amount of energy in 1963 two of their collaborators Fred Hoyle and really Fowler published a paper in which they they argued that such a huge source of energy could only be a supermassive black hole some kind of hypothetical super star where the nuclear reactions going on inside it simply could not provide enough energy most of you are probably familiar with a concept of energy particularly if you pay and electric bill well where is the electric company get that energy from well one possibility is something like this this is the itaipu hydroelectric dam it's very tall it's about 40 stories from bottom to top there that's like a big skyscraper at the top of the dam up here upstream is the water and we say that this water has gravitational potential energy that means it has the potential to convert and produce other forms of energy so the dam the water falls over the dam here falls down 118 meters and as it does that it is accelerated by the Earth's gravitational speed and as it as it gains speed the gravitational potential energy is changed into energy of motion and that rushing water the bottom of the dam drives turbines and generators to make the electric current which is then shipped off and heats and lights people's houses and so on the hydroelectric dam like this is a very good analog of how a supermassive black hole produces energy here the water is only falling down 118 meters matter falling into a black hole will fall trillions of kilometers that's further than the outer regions of the solar system a good fraction the way to the nearest star and it's being serrated not by the gentle gravitational pull which is holding us down on our seats right now it's being accelerated by the tremendous gravitational pull of the black hole if we calculate how much energy is being produced there for let's say one kilogram of material falling into a black hole it's enormous it's more than a nuclear explosion of this material would generate well a mere five weeks after Hoyle and Fowler had published their paper the same Journal carried some papers that identified this object scored 3c273 looks like a bright star and indeed that was what people had previously thought it was but astronomers at Caltech showed that this is in fact a distant active galactic nucleus and it's very bright and it's very far away and the brightness of this is more than hundreds of times greater than the brightness of an entire bright galaxy of a trillion stars we can appreciate that in this Hubble Space Telescope picture up here these little blurry patches which you might not be able to see over here those are entire galaxies like our own but it's look how bright 3c273 is it's brilliantly bright here compared to these ordinary galaxies over here it's so blindingly bright that we can't even tell that it's located in a galaxy there that of course caused enormous excitement among astronomers and pretty quickly a whole lot more objects like this were being found in 1969 the English astrophysicist Donald Lyndon Bell argued a very important point he said well if objects like this by 3c273 faraway in the distant universe in the past were being powered by supermassive black holes then in nearby galaxies there must be boremont black holes because a supermassive black hole is simply not going to go anywhere overnight and a large body of research continuing down to this present day by many astronomers as shown that this is indeed the case we now think that every massive galaxy has a supermassive black hole in its center the nearest and best example of this is actually our own galaxy the Milky Way the center of the Milky Way the nucleus the Milky Way is about 25,000 light-years away in direction the constellation of Sagittarius but you will not be able to see it with your eye but because there's a lot of dust in space in the way however very large telescopes using infrared cameras can penetrate the dust and get us pictures of what's going on there and I want to show you a time-lapse movie which is based on images taken by the European Southern Observatory's Very Large Telescope or VLT in Chile notice there's nothing at the cross there notice that and each one of those blobs there's a star and I click to start the movie then the date of observation if you're wondering when it was will appear up there ok so you can see that the stars are moving around this is from year to year here and they're moving fastest around this cross in the middle here let's zoom in on the cross and watch these stars are going around in elliptical orbits there and let's watch again to this star number 2 up there astronomers have real exciting names for stars here it comes to comes around here zips around that cross at high speed there well we can use Newton's laws of motion use law of gravity to calculate what force you need to make that star swing round like that and how much mass is needed if it's done by gravity which it is and that comes out to be over 4 million times the mass of the Sun well notice the obvious thing there there isn't anything at the location of the Cross there if there's 4 million solar masses were in some kind of hyper super star powered by nuclear reactions as our Sun is that would be a blindingly bright star so bright that that picture we completely washed out and white and you wouldn't be able to see anything up there instead the stars are orbiting around 4 million solar masses of darkness over there these observations are our clearest proof that supermassive black holes do indeed exist there's now no reasonable doubt that in the nuclei of galaxies there are supermassive black holes well how do you feed a black hole let me tell you something about black holes black holes do not suck black holes are not some kind of cosmic vacuum cleaner going around sweeping up sucking up everything around them it is in fact rather hard to go into a black hole the reason for this is that except when you're extremely close to the black hole gravity is a black hole is pretty normal it's just like any other gravity in the universe the earth is orbiting the Sun if the Sun were suddenly to turn into a black hole and don't worry it won't happen but if it did if the Sun suddenly became a black hole well the earth would just keep on orbiting around the Sun it'll be dark that's all but the earth will keep going around in the same orbit let's watch go back to our little movie of the center of our galaxy and zoom in again and again let's watch this star - at the top here go slowly first a little bit like Halley's Comet clear around the Sun it speeds in and zips around there the important point here is star 2 there watch it again is not getting sucked into the black hole to go into a black hole that star would have been on a direct collision course with the black hole and that's probably not going to happen because the black hole is really small so it's gonna miss and it's gonna go flying off this matter going the black holes is mostly gas or is entirely gas and the thing about gas is gas doesn't easily pass through gas if you've seen a couple of fires burning with columns of smoke when the smoke comes together they doesn't pass through like this and keep on going it comes together and it swirls together in one column of smoke well Donald Lyndon Bell recognized that gas that was falling in towards a supermassive black hole was going to end up swirling together and end up spiraling around it and settling down into we caught an accretion disk now disks are quite common in astronomy this is a the best-known nearby example the rings of Saturn the rings of Saturn are particles of dust and ice orbiting together around Saturn here in a very thin plane the material into black hole is actually not dust and ice like Saturn's rings they're it's gas gases and liquids have a special property that we call viscosity viscosity means that one part of a gas is pulling another part of one part of liquid it's pulling on another part and I've got a little demonstration to show this over here so here I have a jar and inside this jar is an apple I just thought if we can do an experiment with gravity than Apple was the right fruit to use if I take this Apple here in the jar I turn the jar upside down you all know what's going to happen it's going to fall down on the ground so here we have a fine Apple who would like an apple in my other jar over here I have something different this is a jar of honey organizers won't mind if I tip this honey upside down upward on the carpet right oh it's not down very quickly is it that's because honey is viscous and the viscosity of the honey means that there's a blob in the middle which would like to fall down on the floor make a mess on this nice red carpet here but it's being held back by the viscosity of the honey which is around it and that honey in turn is being held back by the edge of the jar there well a similar thing happens in the accretion disk the viscosity in the gas is not quite like the viscosity in the honey it's actually provided by tangled up magnetic fields but let's have a look I decide on rings again what you can probably tell from this picture here is that the inner part of the Rings is going faster than the outside part you can see sort of directly dragged off here this is like the planets going around the Sun mercury the closest planet a Sun goes faster than Venus and explanatory it goes fast in the earth and so on the gas on the faster orbits is being held back by the gas further out and that's going to slow it down it's gonna make you go into lower orbit and thus spiral into the black hole so Donald Lyndon Bell proposed that that is how you go inside a black hole well viscosity doesn't just make stuff go into a black hole does something else as well and let's do a little demonstration of the other thing that it does if you can could you take your two hands and squeeze them together and then I want to push hard and then rubbed up really hard and really vigorously okay what's happening they're getting hot and you're moving your hands pretty slowly here inside the accretion disk the gas inside is going faster than the gas outside we call this a differential motion the differential motion between your hands here and the friction between them generates heat that you fairly quickly feel the viscosity in the accretion disk is like the friction in your hands and this is going to heat up that gas enormously it's going to heat it up so much that it's going to become white-hot and that is the cause of the brilliant light we're seeing from 3c273 there and that is also how those Dark Star postulated by the Reverend John Mitchell over two centuries ago turn out to be the most powerful sources of energy in the universe thank you [Applause]

Channel: TEDx Talks

Views: 551,226

Rating: 4.8508215 out of 5

Keywords: TEDxTalks, English, Science (hard), Astronomy, Physics, Science, Space

Id: Zo4gRhG90S4

Length: 17min 59sec (1079 seconds)

Published: Fri Feb 16 2018

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