1 00:00:04,620 --> 00:00:11,380 Okay. Good evening, ladies and gentlemen. Thank you for coming to this 14th fancy lecture. 2 00:00:12,430 --> 00:00:21,130 I don't know whether you're aware of this, but the planning for these lectures is done in great detail, and the dates are chosen very carefully. 3 00:00:21,760 --> 00:00:29,110 So today we are going to have a lecture from a very eminent European astrophysicist, and today is stone. 4 00:00:30,670 --> 00:00:33,820 So that's very appropriate. Thank you for coming on Star Wars Day. 5 00:00:34,750 --> 00:00:43,240 So I particularly like to welcome the pupils and teachers and say parents I understand from Parker School near Bristol, thanks for coming. 6 00:00:43,840 --> 00:00:47,470 I think some of you have been before, so that's terrific. 7 00:00:47,800 --> 00:00:51,170 And it's great to have you here. 8 00:00:51,190 --> 00:00:56,410 You've come back a long way, so thank you for coming. So let me introduce the speaker. 9 00:00:56,680 --> 00:01:05,560 So our 14th lecturer is Professor Connie S, who's the director of Institute of Astronomy at the Catholic University in London. 10 00:01:05,950 --> 00:01:11,590 She also holds an appointment at the University of Nijmegen in the Netherlands. 11 00:01:12,220 --> 00:01:20,050 And in addition to her role as director of institute astronomy, she's also the vice dean for communication and outreach in the Faculty of Science. 12 00:01:20,410 --> 00:01:25,990 So you can imagine that she's pretty used to giving talks in formats like this. 13 00:01:26,680 --> 00:01:30,010 Connie is a world expert on the structure and evolution of stars. 14 00:01:30,790 --> 00:01:41,660 She has some remarkable qualities. She was the first person to ever be awarded consecutive senior research grants from the European Research Council. 15 00:01:41,980 --> 00:01:45,690 I think she's probably the only person to have that honour. 16 00:01:45,930 --> 00:01:50,680 But that's a slightly larger claim that I could actually prove, so I put it that way. 17 00:01:51,130 --> 00:01:59,200 She's also a champion of women in science, and so she has that in common with a previous intellectual, McGorry, 18 00:02:00,000 --> 00:02:06,430 from Yale, who was the American Astronomer Society president when she gave a lecture about eight months ago. 19 00:02:07,450 --> 00:02:16,060 Connie has been widely recognised for the for her accomplishments most recently, and I'm going to read this, I'm afraid. 20 00:02:16,510 --> 00:02:24,280 Last year she was made a commander of the Order of Leopold by the King of Belgium, King Felipe. 21 00:02:24,580 --> 00:02:30,640 This is the highest civilian recognition that's offered by the for services to the Kingdom of Belgium. 22 00:02:31,480 --> 00:02:40,540 In 2012, she was awarded the Franky Prize, which is like the Nobel Prize in Belgium, but she was awarded that by King Albert. 23 00:02:40,720 --> 00:02:48,070 She's also an honorary fellow of the Royal Astronomical Society and does a host of other things that I could say, but there isn't time. 24 00:02:48,970 --> 00:02:53,650 So it's a great pleasure for me to introduce her to give the 14th NC lecture. 25 00:02:53,890 --> 00:02:57,760 Star Quakes Exposed. Stellar Heartbeats. Colony Arts. 26 00:03:06,260 --> 00:03:16,790 Thanks a lot for this introduction and thank you all for coming and giving me the opportunity to give a public lecture on my passion, 27 00:03:17,240 --> 00:03:24,980 which is astronomy in general, but stars particularly, and I wanted to study them ever since I was in primary school. 28 00:03:25,550 --> 00:03:30,470 So I hope I can convey some of the recent findings that we have in this field. 29 00:03:30,980 --> 00:03:36,560 And I'm also very happy to see young people in the audience and less young people. 30 00:03:38,210 --> 00:03:46,730 So I'm used to ages between four and 99 when I give lectures in school and all other types of fora. 31 00:03:47,360 --> 00:03:51,380 So let's see how stars live. 32 00:03:51,920 --> 00:04:00,950 And I'm trying to explain to you why that's a very interesting field in astronomy, particularly in this area. 33 00:04:01,520 --> 00:04:10,399 And so usually I begin by explaining that stars are really hot gaseous spheres and they radiate, 34 00:04:10,400 --> 00:04:14,840 and they do that thanks to nuclear fusion in their core. 35 00:04:15,200 --> 00:04:20,000 So in order to be able to do that, we cannot do that safely on these planets. 36 00:04:20,720 --> 00:04:33,290 We need a high temperature. And so to set the scene, the sun, the surface to see here has a temperature and its surface of about 5500 degrees, 37 00:04:33,680 --> 00:04:36,979 but in its interior, it's millions of degrees. 38 00:04:36,980 --> 00:04:46,430 And that's what you need to do. Nuclear fusion and to create radiation from planets cannot do that. 39 00:04:46,760 --> 00:04:54,500 So here you see an image of the planets of our solar system, and you do see them shining in the night sky, 40 00:04:55,280 --> 00:05:02,180 even though this may not so be obvious in Oxford and it's even less obvious in Belgium. 41 00:05:02,210 --> 00:05:05,600 So called for two. So they shine. 42 00:05:06,200 --> 00:05:09,559 But that's not because they create nuclear energy. 43 00:05:09,560 --> 00:05:14,660 They are not massive enough for that, but they reflect the solar, right? 44 00:05:15,350 --> 00:05:21,500 So this is reflection of the host star's radiation. 45 00:05:21,710 --> 00:05:22,670 That's something different. 46 00:05:23,030 --> 00:05:32,600 And that tells you immediately why we have a hard time to search planets in the galaxy and it's much easier to see the stars. 47 00:05:32,900 --> 00:05:36,379 Okay, so that's just the difference. Keep that in mind. 48 00:05:36,380 --> 00:05:45,380 I will come back to that. So far, the first a lesson on the difference between stars and planets. 49 00:05:45,380 --> 00:05:49,990 That's a question that tends to pop up when we give public those. 50 00:05:50,150 --> 00:05:55,340 Why do we want to bother about stars? Well, for me, stars are the building blocks of universe, 51 00:05:55,940 --> 00:06:04,580 and some other experts in astronomy might say no galaxies are the building blocks of the universe, but galaxies are made of stars. 52 00:06:04,790 --> 00:06:10,069 And so if we want to understand how they live, they have billions and billions of stars, 53 00:06:10,070 --> 00:06:14,510 and there are billions of galaxies in this expanding universe where we live in. 54 00:06:15,140 --> 00:06:23,270 So one of the issues is that we better understand how the stars live, because then we can understand better how galaxies see. 55 00:06:23,690 --> 00:06:29,570 And so in that sense, stars are, for me, really the bricks of the universe. 56 00:06:30,410 --> 00:06:37,700 Stars get born out of very cold, dense clouds in our Milky Way. 57 00:06:37,700 --> 00:06:41,180 So our Milky Way's one galaxy, it has a galactic plane. 58 00:06:41,600 --> 00:06:48,679 And we see inside that plane mainly it's also a little bit above it, really dark areas that you see here. 59 00:06:48,680 --> 00:06:55,580 And these give rise to names that people use their fantasy to name these clouds. 60 00:06:57,470 --> 00:07:01,490 And this is dark here. Not because there are no stars or there's nothing. 61 00:07:01,490 --> 00:07:07,490 No, because there's material dust mainly that blocks the light from the stars behind it. 62 00:07:07,820 --> 00:07:16,219 And so these clouds, they when they get disturbed by one or the other reason they can collapse, 63 00:07:16,220 --> 00:07:21,320 and when they collapse, they form stars many, many stars at the same time. 64 00:07:21,590 --> 00:07:25,160 So stars are born in groups. We call them clusters. 65 00:07:25,550 --> 00:07:33,220 So our sun was also born in such a group, but now our sun is isolated. 66 00:07:33,260 --> 00:07:40,639 Luckily for us, it's a stable environment here because when these clusters pass through the Milky Way, 67 00:07:40,640 --> 00:07:45,470 they get disrupted depending on how close they are together. 68 00:07:46,310 --> 00:07:54,170 So this stellar birth is something that we have yet to understand better because it happens in very cold environments. 69 00:07:54,590 --> 00:08:00,440 And so cold environments are difficult to probe with our eyes mainly. 70 00:08:01,010 --> 00:08:04,580 And we need specific instrumentation but in any way. 71 00:08:05,420 --> 00:08:08,990 Stars get born. They live their life and they die. 72 00:08:09,020 --> 00:08:16,250 And we want to understand how that works. Nowadays we can see that stars when they get born. 73 00:08:16,760 --> 00:08:25,280 So each of these, let's say, entities in such a cloud collapses under its own gravity and it contracts. 74 00:08:25,280 --> 00:08:28,910 And when you contract things, when you put things together, you heat up. 75 00:08:29,310 --> 00:08:32,900 Yeah, I shall not do the experiments here in the audience. 76 00:08:32,900 --> 00:08:38,250 But if I were to squeeze you in a tiny area, you would also heat up, so to speak. 77 00:08:38,300 --> 00:08:47,510 Right. And they do that until they reach a very high temperature, a temperature high enough to create fusion. 78 00:08:47,930 --> 00:08:58,850 And at that point, we call it the star. Now, when they do that, there's always some leftover material that's left behind, and that's what created us. 79 00:08:59,450 --> 00:09:05,650 So we could say that we are sort of the rubbish that was left over when the sun formed. 80 00:09:05,660 --> 00:09:10,720 That's perhaps not so positive way of looking at us, but that's the way it is. 81 00:09:10,760 --> 00:09:18,740 Yeah. So stars have here is a model theoretical computation of a star that gets born and it has some 82 00:09:19,040 --> 00:09:25,040 surrounding material that then is being put in a disk and planets can form out of that material. 83 00:09:25,250 --> 00:09:32,640 We can nowadays see that by infrared instruments, either in space missions or from the ground. 84 00:09:32,660 --> 00:09:37,940 This is an image of the VLT, the very large telescope in the Atacama Desert. 85 00:09:38,060 --> 00:09:42,800 That's a very pleasant place to go if you ever get the chance and haven't done that. 86 00:09:43,190 --> 00:09:46,070 It's a magnificent observatory. 87 00:09:46,730 --> 00:09:58,160 And so we see that, in fact, these are stars where the central star is blocked to show that there is remnant material that then may create planets. 88 00:09:58,700 --> 00:10:05,600 So the message is stars of planets are formed together so they have more or less the same age. 89 00:10:06,080 --> 00:10:13,100 And one of the key issues that we want to understand is how old stars are and how we can deduce their age. 90 00:10:13,370 --> 00:10:19,700 So as an asset, you immediately get the age of the planetary system around the star, around the host. 91 00:10:20,090 --> 00:10:23,630 Okay. Now how do stars work? 92 00:10:23,720 --> 00:10:32,260 So here I'm explaining how the nuclear fusion inside the stars typically stars like the sun. 93 00:10:32,270 --> 00:10:37,490 Let's take our own sun. You know we best why they radiate. 94 00:10:38,240 --> 00:10:49,220 And so a nuclear reactor inside the inner parts of the star is way more efficient than what we can do here on Earth. 95 00:10:50,030 --> 00:10:59,120 So stars are super experts in nuclear fusion, and the sun is doing the simplest nuclear fusion one can imagine. 96 00:10:59,570 --> 00:11:05,390 And that is starting from the very simplest chemical element that we know, which is hydrogen. 97 00:11:06,260 --> 00:11:12,290 So the hydrogen atom consists of an inner proton and an electron circling around it. 98 00:11:12,800 --> 00:11:19,460 And when you push four of these very, very close together, so you create a very high temperature, 99 00:11:19,670 --> 00:11:24,800 pressure and density, then these can melt together and that creates energy. 100 00:11:25,280 --> 00:11:31,100 Why is that? Well, four of those together make up one helium atom. 101 00:11:31,220 --> 00:11:39,470 And you see that from here. And in this helium atom, you will have four nuclear particles, two electrons. 102 00:11:39,650 --> 00:11:46,340 And so the mass of this helium atom is lower than the sum of the masses of these four. 103 00:11:47,150 --> 00:11:53,270 And so then we can use Albert Einstein, most famous formula. 104 00:11:53,630 --> 00:12:02,600 He invented general relativity. But I think if you ask people in the streets, where do you what's the famous formula of Albert Einstein? 105 00:12:02,600 --> 00:12:06,020 They would say yes and see squared. Yeah. 106 00:12:06,410 --> 00:12:16,969 So a little bit of mass is lost from this towards this and that mass multiplied by the speed of light squared, gives you energy. 107 00:12:16,970 --> 00:12:20,540 And that's the energy that the stars radiate. 108 00:12:20,880 --> 00:12:22,880 Yeah. So in that sense, 109 00:12:24,170 --> 00:12:34,940 stars can create nuclear energy and planets cannot because they do not have a high enough temperature in the centre while the stars still have it. 110 00:12:35,750 --> 00:12:39,920 How long can a star do that? Because this in fact sets the life of a star. 111 00:12:40,070 --> 00:12:47,420 It must be able to create energy to counterbalance gravity that wants to, you know, push the layers together. 112 00:12:47,570 --> 00:12:51,170 Well, it can do that as long as it has hydrogen, of course, 113 00:12:51,170 --> 00:13:00,270 because if there is no hydrogen left in the region where the density and temperature is high enough, then the nuclear reactor suddenly stops. 114 00:13:00,290 --> 00:13:03,800 I call that's an energy crisis. And so. 115 00:13:05,250 --> 00:13:11,400 It depends on the amount of matter and the amount of gas that the star got at its birth. 116 00:13:11,820 --> 00:13:15,720 On how long it can live through nuclear fusion. 117 00:13:16,290 --> 00:13:22,880 I want you to appreciate the stars, as I did from very early on, though not because I realised all this. 118 00:13:22,890 --> 00:13:27,660 Not at all. But stars created all elements of the chemical table. 119 00:13:27,690 --> 00:13:34,620 So here you see all the elements that we know. At the early universe there was only hydrogen and helium. 120 00:13:34,650 --> 00:13:42,240 So these two boxes and a tiny little bit of lithium and all these other chemical elements were made by stars. 121 00:13:42,270 --> 00:13:50,280 So I always say medical doctors look at your body in a different way than I do because you're just stardust. 122 00:13:50,790 --> 00:13:58,410 Yeah, that's what we are made of. This is a bit weird to think of us like that, but that's how it is. 123 00:13:58,800 --> 00:14:05,430 So of course we want to appreciate that, but we also want to understand exactly how that works. 124 00:14:06,660 --> 00:14:13,170 And so the nuclear fusion of hydrogen turned into helium happens in the in the sun. 125 00:14:13,170 --> 00:14:19,680 Right now, the sun is doing that in the area where it's hot enough to do this nuclear burn. 126 00:14:20,040 --> 00:14:31,980 Okay. And so we want to know how long the sun can still provide us with that energy so that we know what's going to happen to our solar system. 127 00:14:32,820 --> 00:14:37,500 Because stars get born, live their life, and then they die. 128 00:14:37,740 --> 00:14:41,220 Yeah. And so this is a timeline of the solar life. 129 00:14:42,540 --> 00:14:51,470 After its birth, it lives its life quietly, regularly fusing hydrogen into helium. 130 00:14:51,750 --> 00:15:01,559 And it can do that for a long time. In the case of the sun, about 10 billion years, as you can see here on this graph. 131 00:15:01,560 --> 00:15:04,620 And we are about halfway, let's say, with the sun. 132 00:15:04,890 --> 00:15:11,010 Yeah. Now, the more mass the star has at birth, the shorter its life. 133 00:15:11,040 --> 00:15:18,600 That's a bit weird, perhaps, but that's because it consumes more of the energy because it radiates much stronger. 134 00:15:18,990 --> 00:15:22,530 Okay. So it doesn't last that long. 135 00:15:22,680 --> 00:15:28,200 That's it. But for the sun, we know we're about halfway, which is smooth with its nuclear burning. 136 00:15:28,620 --> 00:15:30,280 And what will happen then? 137 00:15:30,300 --> 00:15:40,470 Well, if there is no longer any hydrogen in the in the core of the sun, which is the nuclear reactor, then the sun is it's an energy crisis. 138 00:15:40,740 --> 00:15:44,580 It can no longer produce the counterbalancing force of gravity. 139 00:15:44,820 --> 00:15:48,300 So it has to come up with something different. And what can it do? 140 00:15:48,660 --> 00:15:54,090 Well, it can try to fuse helium and create heavier elements. 141 00:15:54,520 --> 00:16:03,360 Yeah, that's the only thing it can do. But to do that requires a temperature that's ten times higher than fusing hydrogen. 142 00:16:03,900 --> 00:16:09,270 So how can you make sure that it's hot enough to fuse helium? 143 00:16:09,780 --> 00:16:16,880 Well, how do you make things hotter? You push things together so the sun will start constructing its inner parts. 144 00:16:16,890 --> 00:16:23,550 That's at that point, helium. And as a as a counter reaction, it will start expanding. 145 00:16:24,450 --> 00:16:29,670 And this expansion will mean that the sun will become what we call a red giant star. 146 00:16:29,910 --> 00:16:31,980 And that's what you see indicated here. 147 00:16:33,750 --> 00:16:45,780 This is not pleasant for us as an outlook because the sun will become really big and we know more or less when it will happen, 148 00:16:45,990 --> 00:16:50,720 you know, more or less how big it will be, but not very precisely. 149 00:16:50,820 --> 00:16:53,370 And that's one of the things we want to learn better. 150 00:16:54,690 --> 00:17:04,350 So that's not something to worry about because it will not happen in your lifetime, not the one of your grandchildren or their grandchildren. 151 00:17:04,830 --> 00:17:06,479 It will take a billion years. 152 00:17:06,480 --> 00:17:22,800 So we have some time to do some thinking about how to say what to do now in order to improve the models that we have and the predictions, 153 00:17:23,070 --> 00:17:33,930 we need to know the details about how the physics in the interior of the sun is to a better precision that we can do now. 154 00:17:35,160 --> 00:17:39,370 And so one of the key issues is how stars die. 155 00:17:39,960 --> 00:17:44,280 We know that more or less also for the sun and when it will take place. 156 00:17:44,280 --> 00:17:50,010 We know it more or less, but not very precisely. And stars can die, in fact, in two ways. 157 00:17:50,880 --> 00:17:52,500 And it can lead to three products. 158 00:17:52,500 --> 00:18:05,000 And so stars like the Sun will become a red giant, will expel the material, and will give rise to a dying star called the White Dwarf. 159 00:18:05,090 --> 00:18:10,460 Which is, in fact a carbon oxygen bowl at the size of the Earth, more or less. 160 00:18:10,790 --> 00:18:17,410 And this goes quietly so it will not explode. Stars that get born with a lot more mass than the sun. 161 00:18:18,770 --> 00:18:24,740 They live much shorter lives, and they end their life explosively. 162 00:18:25,520 --> 00:18:34,130 They manage to burn helium into carbon and then carbon into heavier elements until they reach iron and then they explode. 163 00:18:34,340 --> 00:18:38,240 Yeah, these stars are very different from our sun. 164 00:18:38,780 --> 00:18:51,980 So I'm not bothered today with these stars because they don't have planets and we don't have to worry about the sort of future being along this path. 165 00:18:52,280 --> 00:18:57,140 So in the end they explode and they can give rise to a neutron star or a black hole. 166 00:18:57,290 --> 00:19:01,310 But this is a very different type of life that they lead compared to our sun. 167 00:19:03,230 --> 00:19:08,719 Now, at the moment when the sun hits the energy crisis, it will sort of look a bit like this. 168 00:19:08,720 --> 00:19:13,310 This is an artist's impression. Just to clarify, this is not a real image. 169 00:19:14,090 --> 00:19:22,249 And so the sun will somehow come very close to earth, and the predictions are that its radius will pass to Earth. 170 00:19:22,250 --> 00:19:25,590 So it will eat us, if you like. 171 00:19:26,180 --> 00:19:31,970 And then we'll end it somewhere with this radius between the Earth and Mars. 172 00:19:32,510 --> 00:19:41,780 Where exactly? We don't know. So we have a desire, so to speak, to try and understand how large stars are. 173 00:19:42,170 --> 00:19:50,629 These things easy, but it's not. Because if you look at the night sky, even with our big telescopes, stars are not resource. 174 00:19:50,630 --> 00:19:54,980 We can't resolve the surface. They are tiny little dots that's shiny, right? 175 00:19:55,400 --> 00:20:02,390 And so we have to come up with a way to estimate the size or the radii of stars in a better way. 176 00:20:03,260 --> 00:20:06,709 I can also not wait and do the experiments until the sun dies. 177 00:20:06,710 --> 00:20:09,770 We don't want to do that. We want to be a bit more proactive. 178 00:20:09,770 --> 00:20:13,759 Let's say no. And so stars live millions to billions of years. 179 00:20:13,760 --> 00:20:18,380 We can't wait and see what happens to improve our theory. 180 00:20:18,710 --> 00:20:24,020 That's far too slow. And what do we do to solve that? 181 00:20:24,050 --> 00:20:34,280 Well, we take stars like the sun in different stages of their life, and we try to put the pieces of the puzzle together to improve our theory. 182 00:20:34,670 --> 00:20:39,410 But then, of course, we also want to test these theoretical findings, so to speak. 183 00:20:39,800 --> 00:20:48,120 And so that's one of the issues where our field of research has made a lot of progress the last decade now. 184 00:20:48,740 --> 00:20:56,240 And so I always come up with Eddington, who was sort of considered the father of stellar structure, 185 00:20:56,780 --> 00:21:01,790 who was very frustrated in his book, The Eternal Constitution of Stars. 186 00:21:01,830 --> 00:21:09,080 Yeah, it's almost well, it's no, it's more than 90 years old, meanwhile, but still a very illustrative book to read. 187 00:21:09,620 --> 00:21:14,410 And his frustration was that we couldn't do experiments on the interior of stars. 188 00:21:14,990 --> 00:21:23,390 We cannot grab a part of the sun and do laboratory experiments, as experimental physicists can do. 189 00:21:23,600 --> 00:21:29,270 We have to come up with some more original way of doing the testing now. 190 00:21:30,470 --> 00:21:36,770 And so he wondered what appliance can ever pierce through the outer layers of a star and test the conditions within? 191 00:21:37,160 --> 00:21:40,420 And now we know at least one answer how to do that. 192 00:21:40,430 --> 00:21:45,800 And that's the topic of today. It's something that we call astro seismology. 193 00:21:46,940 --> 00:21:59,690 So differently. This is the study of star quakes, as I tend to call it, because it's a bit more easy to understand if you compare with earthquakes. 194 00:21:59,780 --> 00:22:04,490 And in fact, the the mathematical treatments is the same. 195 00:22:04,700 --> 00:22:11,240 So what the geologists here of the Earth do, well, they love earthquakes, 196 00:22:13,100 --> 00:22:18,650 particularly quakes that they involve themselves in that are modest in in amplitude. 197 00:22:18,720 --> 00:22:30,560 Yeah, they love that. Why? Because earthquakes create waves that travel through the earth, that bounce back at the and a silicon core of the earth. 198 00:22:30,560 --> 00:22:36,380 And then the waves travel back and their seismographs measure the travel time of these waves. 199 00:22:36,770 --> 00:22:46,460 And the travel time tells you where the cause of our planet's and how big it is and what its chemical composition could be. 200 00:22:47,090 --> 00:22:52,070 So waves are a very powerful tool for physicists in general. 201 00:22:52,380 --> 00:22:57,170 Now, I cannot drill a hole here until I reach the core of the earth. 202 00:22:57,380 --> 00:23:03,050 That's frustrating, right, for geophysicists. Well, I cannot look inside. 203 00:23:03,050 --> 00:23:09,790 The star is the same, but stars. Earthquakes and quakes create waves so we can do the same physics. 204 00:23:10,210 --> 00:23:15,010 And this has become possible because we can observe these star quakes. 205 00:23:15,490 --> 00:23:30,190 Now, how does that work? Well, so first of all, this work means that we know the stars, their oscillations, and we are clever people. 206 00:23:30,190 --> 00:23:36,380 So we could sort of do a reasoning using these oscillations and then understand the stellar interior. 207 00:23:36,400 --> 00:23:42,520 So this is what Eddington couldn't do because he didn't have the data to do that. 208 00:23:43,480 --> 00:23:49,630 And so here in this drawing, I've given a cartoon like picture of how that works. 209 00:23:50,050 --> 00:23:53,800 So you have this star just like you have the earth. 210 00:23:54,070 --> 00:23:57,639 There are quakes going on. These quakes create waves. 211 00:23:57,640 --> 00:24:02,620 And here are four types of waves the red, yellow, green and purple one. 212 00:24:03,970 --> 00:24:10,200 And these quakes move in the interior of the star and they bounce back up. 213 00:24:10,870 --> 00:24:15,010 And this happens inside the star. It happens inside the sun right now. 214 00:24:15,580 --> 00:24:22,120 We don't notice that as human beings here, because the soul of quakes are very, very tiny. 215 00:24:22,480 --> 00:24:25,510 And that's in general the case for most of the stars. 216 00:24:26,140 --> 00:24:33,760 Now, imagine that you follow such a wave, and here is a many patterns of the green and the yellow one, 217 00:24:34,030 --> 00:24:41,300 because these quakes have almost the same periodicity, the same frequency. 218 00:24:41,320 --> 00:24:46,510 Yes. So imagine the stellar surface goes, you know, in a complicated way up and down. 219 00:24:46,990 --> 00:24:54,610 And it does that with the certain periods or frequency, like that's one over the period. 220 00:24:55,480 --> 00:25:01,150 And then you follow these waves as they probe the physical properties in this yellow layer, 221 00:25:01,570 --> 00:25:04,990 and the green one does the same, except it goes a little bit deeper. 222 00:25:05,500 --> 00:25:09,100 So some of the waves manage to go a bit deeper than the others. 223 00:25:09,550 --> 00:25:12,820 And so what are what do we want to do? 224 00:25:13,060 --> 00:25:20,470 We want to have the Green Wave study and the yellow one, and each has their own frequency. 225 00:25:20,650 --> 00:25:23,590 If we subtract these two frequencies from each other, 226 00:25:23,980 --> 00:25:29,650 then we get the information of the area in the star, which is green on this cartoon and not yellow. 227 00:25:30,010 --> 00:25:35,510 That tiny little layer is felt by the green wave, but not by the yellow. 228 00:25:35,520 --> 00:25:45,300 With as so, its properties are a bit different and that property difference is connected or is determined by the physics inside that layer. 229 00:25:45,960 --> 00:25:53,800 Okay, so if we can do that for a whole lot of these waves, then we can build up the physics layer by layer inside this stuff. 230 00:25:53,950 --> 00:25:59,610 That's how it works in practice. There's a whole mathematical scheme behind this. 231 00:25:59,620 --> 00:26:08,390 I will not bother you by that. But the picture that is in this cartoon sort of gives you a handle on how we do these things. 232 00:26:09,010 --> 00:26:15,010 Now these waves propagate inside the star. They don't come towards us. 233 00:26:15,310 --> 00:26:19,870 The sun for the moment is has quakes. Hundreds of solar quakes. 234 00:26:20,680 --> 00:26:26,050 You don't notice this when you look at the sun and you can try, but please protect your eyes. 235 00:26:26,260 --> 00:26:32,530 Yeah, because they have. These are such low amplitude that you cannot see. 236 00:26:33,280 --> 00:26:37,420 But these quakes create sound waves that propagate inside the sun. 237 00:26:37,870 --> 00:26:43,300 Yeah. And so that's a bit similar then. I'm creating sound waves all the time now in this auditorium. 238 00:26:43,930 --> 00:26:50,170 So I have this beautiful cavity here. Sounds is propagating and you can hear me. 239 00:26:50,830 --> 00:26:56,890 Yeah. If this auditorium would have different air inside the inside here. 240 00:26:57,160 --> 00:27:06,430 Let's say there was helium gas here. It would sound I would sound weirdly, the frequency of the sound would change. 241 00:27:07,450 --> 00:27:13,629 So the frequency of an oscillation mode that creates a wave also changes according 242 00:27:13,630 --> 00:27:18,820 to the chemical composition of the medium where the sound waves travel. 243 00:27:19,320 --> 00:27:25,720 Okay. So we can actually make an analogy with sound waves that you're familiar with. 244 00:27:25,840 --> 00:27:32,380 And I tend to do the analogy with respect to music because people like music. 245 00:27:32,710 --> 00:27:37,030 And so let's do a break and the interludes. 246 00:27:37,920 --> 00:27:43,690 Oh, and are there any musicians in the audience? 247 00:27:45,820 --> 00:27:49,380 Don't worry. I will help make you play yourself to be shy. 248 00:27:49,510 --> 00:27:59,799 Okay. Musicians know very well how sound waves work without doing the mathematics of it necessarily, but you know, more intuitively. 249 00:27:59,800 --> 00:28:04,840 Yeah. And so, in fact, the stellar oscillations create sound. 250 00:28:05,100 --> 00:28:08,640 The travel inside the star. But we can't hear them. 251 00:28:09,060 --> 00:28:12,630 Why not? The sound waves are in the concert hall. 252 00:28:13,380 --> 00:28:20,880 As so my concert halls are stars and the sounds don't reach me because there's no medium between me and the stars. 253 00:28:20,880 --> 00:28:27,840 So the sound cannot propagate outside the setup. Okay, so I'm going to have to cheat a little bit. 254 00:28:28,200 --> 00:28:34,920 But what you can all do is, well, my students always have to work. 255 00:28:35,220 --> 00:28:39,750 You're my students now. So I will do an exam. 256 00:28:41,250 --> 00:28:51,030 It's not going to be difficult. And I sometimes I do it with real musicians, but now I have a limited amount of time and I'm another. 257 00:28:51,560 --> 00:28:56,080 Another musician myself with it. Really? Let's do a thought experiment. 258 00:28:56,130 --> 00:28:59,340 Right. So I'm showing a musical instrument. 259 00:29:00,420 --> 00:29:06,870 Now, let's say a contrabass, and it can produce sound waves. 260 00:29:07,890 --> 00:29:22,530 And you can listen to it. Now, what would happen if I have another musician and I lets him or her play on this instrument, a tiny little violin? 261 00:29:23,760 --> 00:29:31,650 And the question would be, well, the sounds of this instrument and of this instrument is different. 262 00:29:31,950 --> 00:29:42,090 Right. And so the frequency of this instrument or the tones, if you like, to make more artistic vocabulary. 263 00:29:42,150 --> 00:29:52,979 Yeah. The question is, which of the two will play the highest tones, the big instrument or the small instrument? 264 00:29:52,980 --> 00:29:56,160 And I will do a yes and no. So who votes? 265 00:29:56,760 --> 00:30:01,140 Highest thoughts? This instrument fool. Who thinks that's a good answer? 266 00:30:05,600 --> 00:30:09,380 Hailstones and this instrument were things. That's the correct answer. 267 00:30:10,940 --> 00:30:18,740 You are all seismologists. You notice a smaller instrument gives higher frequencies. 268 00:30:19,130 --> 00:30:29,800 That's something you are familiar with, right? So if I could only listen to the sounds inside the star, then I would know the size of the star. 269 00:30:29,810 --> 00:30:34,520 And that was one thing. We really want to improve our knowledge with that. 270 00:30:35,180 --> 00:30:38,210 So let's try to do an experiment. 271 00:30:38,330 --> 00:30:45,500 The Sun is a musical instrument for me. It's a three dimensional guitar, you could see. 272 00:30:45,860 --> 00:30:51,590 Right? And a one dimensional guitar is played by musicians in this way. 273 00:30:52,640 --> 00:30:59,000 You can play it in the fundamental mode, as it's called, or with the first overtone or the second overtone. 274 00:30:59,240 --> 00:31:08,149 You could also call them harmonics. And so any tune that's being played has an amplitude. 275 00:31:08,150 --> 00:31:15,320 That's the height with which this goes up and down. And it has a periods up and down and up and up. 276 00:31:15,740 --> 00:31:22,930 Or a frequency. Yeah. We tend to work in frequency rather than in period. 277 00:31:22,940 --> 00:31:27,800 And so when I speak of frequencies, you can think of musical tones, so to speak. 278 00:31:29,360 --> 00:31:32,240 And the strength of the sounds is the amplitude. 279 00:31:33,080 --> 00:31:38,960 And so some of my notes have an audio point, and others have two notes and then three notes and so on. 280 00:31:39,110 --> 00:31:46,400 Yeah. So now we turn that into a three dimensional string, let's say, and then you get a stop. 281 00:31:46,850 --> 00:31:50,120 Yeah. And so a star could come. 282 00:31:50,570 --> 00:31:53,960 Can be seen as such a motion. 283 00:31:54,180 --> 00:31:58,430 Yeah. This is one isolation load, and different layers go up and down. 284 00:31:58,550 --> 00:32:01,910 Yeah, this is the. The Stellar Oscillation or the quake. 285 00:32:02,420 --> 00:32:05,920 And we can't look in the interior, but we would like to. 286 00:32:06,110 --> 00:32:09,530 Yeah. And so that's not possible for a star. 287 00:32:09,530 --> 00:32:18,770 We have to somehow find a way to listen to the star's tones through the frequencies without being able to inject ourselves into the star. 288 00:32:18,980 --> 00:32:26,390 Okay, so let's try to do that. And I have first have to confess something. 289 00:32:26,810 --> 00:32:31,700 I want to place you inside the sun and let you enjoy the symphony of the sun. 290 00:32:32,870 --> 00:32:43,820 We unfortunately cannot hear it in our daily life, but I can make a sound file and let you listen to the quakes of the sun. 291 00:32:44,510 --> 00:32:48,360 The problem is that your ears are not well-suited. 292 00:32:48,590 --> 00:32:53,060 You are not in the audible range of the solar earthquakes. 293 00:32:53,570 --> 00:32:59,210 So I made a factor 100,000 to bring it to your audible range. 294 00:32:59,570 --> 00:33:02,960 But I do that with the global symphony, a symphony of the sun. 295 00:33:03,120 --> 00:33:12,470 Okay, so we're not going to listen to the solar quakes as if you're inside the sun and then you can enjoy the symphony of the sun. 296 00:33:13,430 --> 00:33:17,330 In my language, that means the frequencies of the solar oscillations. 297 00:33:17,510 --> 00:33:20,600 Okay. Are you ready? 298 00:33:27,980 --> 00:33:40,840 Just enjoy. Is this a nice symphony? 299 00:33:41,710 --> 00:33:45,280 How lucky we are that we don't have to listen to that all the time. 300 00:33:45,460 --> 00:33:50,060 Okay. That, for me is beautiful. Not particularly the sound. 301 00:33:50,110 --> 00:33:54,159 But what have you heard now? You have heard this symphony of the sun. 302 00:33:54,160 --> 00:34:01,270 And this is measurements from the Soho satellites. But don't forget, I have multiplied by 100 thousands. 303 00:34:01,810 --> 00:34:07,930 And you see here the strength of the sounds versus frequency expressed in microwaves. 304 00:34:08,200 --> 00:34:13,090 And all these lines that go up are the musical tones that you hear. 305 00:34:13,450 --> 00:34:22,240 And the higher the line, the stronger the tone. And so the strongest one for the sun occurs more or less at 3000 micro hertz. 306 00:34:22,930 --> 00:34:26,050 If you turn that into periods, that's about 5 minutes. 307 00:34:26,060 --> 00:34:34,240 So the solar surface experiences a quake, a dominant quake that goes up and down by a period of 5 minutes. 308 00:34:34,240 --> 00:34:36,430 And there are many quakes going on at the same time. 309 00:34:37,600 --> 00:34:46,300 So we can construct this type of diagram and it tells us a lot about the physics of the sun, among other things, its size. 310 00:34:46,600 --> 00:34:52,480 Think of the violin versus contra bass by just measuring these quakes. 311 00:34:52,510 --> 00:35:00,250 Now, we can't listen to them, but what we can measure is that the quakes make the surface parts go up and down. 312 00:35:00,580 --> 00:35:04,420 And this changes slightly the temperature at at the surface. 313 00:35:04,810 --> 00:35:08,010 And this we can measure in light intensity. 314 00:35:08,020 --> 00:35:12,520 So that's the way we observe the quakes, even though we can't listen to. 315 00:35:13,460 --> 00:35:17,930 Okay. And so now we have a quiz number two. 316 00:35:18,590 --> 00:35:25,730 Now I'm going to want to know how the quiz sounds when the sun is about to die. 317 00:35:26,150 --> 00:35:34,800 And, you know, as it will die, it will shrink its core in its inner parts to make it harder for nuclear fusion of helium. 318 00:35:35,120 --> 00:35:38,569 And at the same time, it will expand its outer layers. 319 00:35:38,570 --> 00:35:42,680 So we're going to make a big star. So we're going to make a big instrument. 320 00:35:43,280 --> 00:35:54,540 So will the frequencies go up or down? Who votes for down the lower frequencies. 321 00:35:54,930 --> 00:36:01,950 So I'm not going to make you enjoy the sound waves of a red giant that has been observed by the Kepler satellites. 322 00:36:02,550 --> 00:36:06,570 And your prediction is that the frequencies should be lower? 323 00:36:07,170 --> 00:36:13,290 Yeah, that's far lower. 324 00:36:14,580 --> 00:36:17,990 And kits like this in Belgian disco since we did this press release. 325 00:36:19,230 --> 00:36:23,890 So sometimes I have to ask questions. Why do you want to ask to support fundamental science? 326 00:36:23,910 --> 00:36:27,690 Well, it has some practical use. Okay. 327 00:36:30,180 --> 00:36:37,110 So this is a red giant. And so here you have strength of the music, so to speak, as a function of frequency. 328 00:36:37,470 --> 00:36:41,910 And now it has beautiful quake's sound waves created. 329 00:36:42,240 --> 00:36:50,010 And it takes it about, let's say, 66, 67 micro hertz, much lower than the sun, which was at 3000. 330 00:36:50,520 --> 00:36:57,360 So this must be a much bigger star. And we scaled and then we know how big the star is while it's a dot on the sky. 331 00:36:57,690 --> 00:37:07,559 Yeah, that's impressive, because the way we can do the sizes of stars in this way is with a relative precision of only a few percent, 332 00:37:07,560 --> 00:37:10,980 while it's, you know, billions of kilometres away. 333 00:37:11,280 --> 00:37:16,520 Yeah. Again, we can't hear this, but we can see the fluctuations on this telescope. 334 00:37:17,010 --> 00:37:22,910 Okay. Is this a bigger star in the sun or a smaller one? 335 00:37:25,010 --> 00:37:31,560 Smaller one. This is typical of the previous one was a cosmic buzzing, cosmic pickle. 336 00:37:33,080 --> 00:37:38,300 This is a tiny star compared to the sun and it has very high tones because of that. 337 00:37:38,310 --> 00:37:41,980 But it's very special in the sense that it is a super star. 338 00:37:41,990 --> 00:37:45,920 It was measured in La Palma with the William Herschel telescope. 339 00:37:46,460 --> 00:37:49,850 So you can also do this science from the ground because it has big quakes. 340 00:37:50,210 --> 00:37:53,230 And you see, that's why the noise level here is larger. Yeah. 341 00:37:53,270 --> 00:37:56,270 Compared to the previous two that were measurements from space. 342 00:37:56,520 --> 00:38:06,710 Oh, less noisy. And so here we are at about 7 million or 7000 micro hertz, which is higher than the sun. 343 00:38:06,870 --> 00:38:09,890 Okay, so this is a very tiny, small star. 344 00:38:10,320 --> 00:38:13,399 Yeah. And it's very faint. So we can. 345 00:38:13,400 --> 00:38:16,820 We can this stellar sizing we can do. 346 00:38:17,300 --> 00:38:20,810 So we can predict in the in the solar life. 347 00:38:21,440 --> 00:38:24,470 How the sun as a red giant. How big it will become. 348 00:38:25,160 --> 00:38:36,820 Oh. And it might be a little bit less bleak by the time it reaches the hydrogen exhaustion than we anticipate. 349 00:38:37,360 --> 00:38:43,030 How does this research field work in practice? Not by making sound files. 350 00:38:43,030 --> 00:38:48,730 That's fun for a public talk because it avoids me to have to show you mathematics. 351 00:38:49,210 --> 00:38:57,240 And mathematics is really fun and beautiful, but it's not for every person in the audience. 352 00:38:57,910 --> 00:39:07,210 So in practice, we measure the quakes by the sort of light intensity metre that we put into space. 353 00:39:07,900 --> 00:39:10,900 We can do this from the ground for very big quakes. 354 00:39:11,080 --> 00:39:11,340 Yeah, 355 00:39:11,950 --> 00:39:21,280 but we can't do it for the majority of stars because the tiny little variations that you want to measure are screwed up by the Earth's atmosphere. 356 00:39:21,940 --> 00:39:26,890 Atmosphere is unstable, and the very people say that stars, twinkle, 357 00:39:27,400 --> 00:39:33,640 stars twinkle is the atmosphere of the earth that makes us think that the stars are right. 358 00:39:34,060 --> 00:39:38,500 And so that destroys our beautiful seismic signal on this stuff. 359 00:39:38,920 --> 00:39:44,740 So we need space missions. And these are two missions that we're operational. 360 00:39:44,890 --> 00:39:50,230 You see now, more than ten years ago, a European and an American one. 361 00:39:50,620 --> 00:39:54,010 And there are unmanned space missions. Sometimes I get the question. 362 00:39:54,700 --> 00:39:58,610 You go up there. Why don't we don't want me up there. 363 00:39:58,630 --> 00:40:03,520 I would screw up the measurements, probably. And so these are scientific missions. 364 00:40:03,760 --> 00:40:07,090 But onboard is an ultra precise. 365 00:40:09,890 --> 00:40:16,790 Seismograph, as I tend to call it, that can measure the tiny little brightness variations as the quakes score. 366 00:40:17,150 --> 00:40:22,460 And we can measure that with the precision that we express as parts per million. 367 00:40:22,970 --> 00:40:32,990 So imagine that we give the equilibrium of the sun when it doesn't have quakes, a value of a million in water in a unit, energy unit. 368 00:40:33,470 --> 00:40:40,010 The quakes make it deviate from that equilibrium and the deviation is one out of a million. 369 00:40:40,430 --> 00:40:46,400 So instead of a million, it would be 1,000,001. And we can measure that or 900 words. 370 00:40:46,700 --> 00:40:54,870 I can't even pronounce that number. Okay. So tiny little fluctuations and we can measure them uninterruptedly because 371 00:40:54,870 --> 00:40:59,359 the space mission is not bothered by a day and night rhythm from the earth. 372 00:40:59,360 --> 00:41:05,570 We are always blocked because now there are plenty of stars, but you can't see them during the day and you can't measure them. 373 00:41:05,690 --> 00:41:09,890 Okay. So that's why we made such big progress in these fields. 374 00:41:10,380 --> 00:41:11,990 And so what are we doing? Practice. 375 00:41:11,990 --> 00:41:18,530 So we know we have all these quakes going on at the surface, and that creates waves that propagate in the interior. 376 00:41:18,830 --> 00:41:23,300 We measure their brightness. They create the variations as a function of time. 377 00:41:23,570 --> 00:41:29,930 And this is one star observed by the Kepler satellites. And this is sort of my seismograph, so to speak. 378 00:41:29,940 --> 00:41:35,150 So you see all these fluctuations. It's not strong here, stronger here. 379 00:41:35,450 --> 00:41:42,170 That's what we call beating of stellar oscillations that strengthen each other here and weaken each other there. 380 00:41:42,470 --> 00:41:50,840 And all these quakes we can measure and these were the diagrams that you just heard for three different stars, strength as a function of frequency. 381 00:41:51,250 --> 00:41:57,890 And so for this star, for instance, it peaks its quakes are strongest at 75 micro hertz. 382 00:41:58,220 --> 00:42:02,030 So, you know, that must be a bigger star than the sun, right? 383 00:42:02,030 --> 00:42:06,200 Because the sun peaks at 3000 micro. So this one was must be bigger. 384 00:42:06,200 --> 00:42:12,520 And that's also what we have for this star is there is more it's more massive than the sun. 385 00:42:12,530 --> 00:42:16,370 And that means it's bigger now. So again, 386 00:42:16,790 --> 00:42:25,820 that's why I showed this movie before we measured the quakes at the surface of the star and the signal that we get in such what we call a light curve. 387 00:42:26,150 --> 00:42:29,810 We can then say something about what is happening inside. 388 00:42:30,230 --> 00:42:33,100 So that's the appliance of Eddington. Yeah. 389 00:42:33,440 --> 00:42:42,740 We can go inside the star by measuring quakes and doing and an interpretation of the seismology of the star. 390 00:42:43,100 --> 00:42:46,250 And here you see four stars observed by Kepler. 391 00:42:46,580 --> 00:42:49,600 You see their light curves only during 20 days. 392 00:42:49,610 --> 00:42:54,769 In reality, we are 1500 days. We have four years uninterrupted data. 393 00:42:54,770 --> 00:43:01,550 And this white curve, you see the fluctuations go up and down faster than this blue curve. 394 00:43:02,510 --> 00:43:06,979 So shorter periods is higher frequency. 395 00:43:06,980 --> 00:43:10,070 That's a smaller star. Yeah, that's typical, you would say. 396 00:43:10,790 --> 00:43:17,550 And so intermediate cases here. So the sizes are not the scale, but you get the picture right. 397 00:43:17,570 --> 00:43:23,570 We observe such a curve. We did use the frequencies of this of the quakes. 398 00:43:23,990 --> 00:43:29,660 And then we know how big it is. So that's it's as simple as that, so to speak. 399 00:43:30,010 --> 00:43:35,280 Yeah. And we can do that nowadays for thousands of stars, thanks to this space mission. 400 00:43:36,710 --> 00:43:43,820 I have, again, something special. And I change this because everywhere I give this talk, it's coffee with milk. 401 00:43:43,820 --> 00:43:52,520 But I'm in your case as a courtesy to the nice tea milk session I had with the students. 402 00:43:54,470 --> 00:44:01,010 Why? What do I mean by that? Well, what do you do when you drink tea here and you want to drink tea with milk? 403 00:44:01,340 --> 00:44:06,590 You pour milk in your cup and you're not going to sit and wait because then your tea gets cold. 404 00:44:07,070 --> 00:44:13,100 By the time that everything is mixed, doesn't mix very efficiently, you take a spoon and you stir. 405 00:44:13,550 --> 00:44:24,020 Right. In my language, you add angular momentum to the mixture of the tea with milk. 406 00:44:24,530 --> 00:44:31,490 So your spoon makes the tea and the nuke rotates and that means the material is better mixed. 407 00:44:31,760 --> 00:44:34,370 And then you can drink it while it's warm, right? 408 00:44:35,180 --> 00:44:46,010 So rotation gives mixing and we don't know how stars rotate in their interior or we didn't know how that worked until a few years ago. 409 00:44:46,190 --> 00:44:49,250 We thought we knew from theory, from theoretical models. 410 00:44:49,580 --> 00:44:54,950 And then came the experiments with the seismology. And it turns out we didn't know how it worked. 411 00:44:55,170 --> 00:44:59,570 Yeah. So why are Star Plates so helpful here? 412 00:44:59,780 --> 00:45:04,130 Well, imagine that I have this violin player. 413 00:45:04,280 --> 00:45:09,050 Yeah. And I let the person play a nice symphony, and I. 414 00:45:09,500 --> 00:45:13,880 Check it a little bit behind the scenes and I make the podium turn around. 415 00:45:14,750 --> 00:45:18,380 Then the symphony screwed for you as an audience. It's horrible. 416 00:45:19,250 --> 00:45:23,630 It's a nice experiment. Sometimes I do that, but then I need the real theatre now. 417 00:45:24,590 --> 00:45:30,740 And that's still to help you think of the fact that rotation. 418 00:45:32,610 --> 00:45:37,770 Shifts the frequencies of all the sound waves, and it screws up the same thing. 419 00:45:38,070 --> 00:45:44,220 Yeah. Now imagine that we have a quake travelling through a star and the star rotates. 420 00:45:45,150 --> 00:45:53,160 Then it shifts the frequencies and we measure frequencies with these satellites so we can compare a 421 00:45:53,160 --> 00:46:02,010 star that doesn't rotate its frequencies with the star that seemingly looks the same from the exterior. 422 00:46:02,250 --> 00:46:08,810 Yeah, but that does not rotate versus rotate strongly in the interior. 423 00:46:09,150 --> 00:46:12,390 And the frequencies will be shifted. And we can unravel that. 424 00:46:12,420 --> 00:46:19,290 That's why I make this analogy. So we have mammoth thanks to very high precision measurements from Kepler. 425 00:46:19,800 --> 00:46:24,380 And this is put in an animation stellar sound. But you know, the sun here, it rotates. 426 00:46:24,390 --> 00:46:30,510 We know how fast it rotates at the surface and we know that for other stars, too, we can measure surface rotation. 427 00:46:30,750 --> 00:46:40,110 But I want to know how the material is mixed inside the star, because if you have rotation in the area where the nuclear fusion is going on, 428 00:46:40,320 --> 00:46:47,460 then you add hydrogen to the core region and it can take part in the energy production and the star can live longer. 429 00:46:47,880 --> 00:46:51,090 So the more mixing, the longer the star lives. 430 00:46:51,360 --> 00:46:55,320 And that gives me a handle on predicting the ages of the stars. 431 00:46:55,650 --> 00:47:01,170 So in this animation done by my former students, Paul Beck, 432 00:47:01,950 --> 00:47:10,290 he unravelled from data from the Kepler mission that the Red Giants have a core that rotates faster than the envelope. 433 00:47:10,620 --> 00:47:19,700 And that's also what theory predicts, because remember I told you, let's assume that the hydrogen is gone in the core of the sun. 434 00:47:19,710 --> 00:47:28,920 What will it do? It will start shrinking its core to make it hotter in an attempt to burn helium, and the outer layers will expand. 435 00:47:29,460 --> 00:47:37,680 And then if you shrink the core, it will start spinning faster and the outer layers are expanding, so they go slower. 436 00:47:38,010 --> 00:47:41,910 So we can expect that a faster core then envelope rotation. 437 00:47:43,350 --> 00:47:47,190 But the models were two orders of magnitude wrong. 438 00:47:48,120 --> 00:48:00,060 So what the quakes tell us is that the cause of red giant stars are a factor 100 slower than what our theoretical models predict. 439 00:48:00,660 --> 00:48:09,720 And that's fascinating, because that means that we can learn something, and it means that we thought we knew things well, but we don't. 440 00:48:10,220 --> 00:48:13,590 And this is what I would still call it, an unsolved problem. 441 00:48:14,580 --> 00:48:18,180 So that's one of the major achievements that we have in this field. 442 00:48:18,630 --> 00:48:22,920 And it's couples to the question I had on my first, like, how old are the stars? 443 00:48:25,470 --> 00:48:32,700 Well, we need to know the amount of matter that can take part in nuclear fusion because that sets the age of the star. 444 00:48:32,910 --> 00:48:40,230 Yeah. And if we want to know how much matter is in the nuclear reactor, we need to understand the rotation inside the star. 445 00:48:41,070 --> 00:48:46,590 Typically, classically, without quakes, we would measure the rotation of the sun at the surface. 446 00:48:46,620 --> 00:48:51,690 You can do that. That's an experiment we do when school children come and visit us. 447 00:48:51,930 --> 00:48:57,600 Why? Because you have seen in the animation the sun has sunspots and they rotate in your line of sight. 448 00:48:57,810 --> 00:49:07,500 Again, don't try to do this without protective glasses, but you can follow that and reduce the surface rotation of the sun. 449 00:49:09,090 --> 00:49:18,210 So for the non astronomers in the audience, what would be the rotation periods of the sun at the surface? 450 00:49:19,060 --> 00:49:23,580 You know, that's. Who knows that? 451 00:49:26,190 --> 00:49:29,819 Isn't that weird? That's our host star. That's our mother star. 452 00:49:29,820 --> 00:49:33,450 And we don't even know how it rotates at the surface. 453 00:49:33,450 --> 00:49:40,500 So we make students derive that. But as there are many astronomers here, it's about 26 days. 454 00:49:41,010 --> 00:49:44,790 Yeah. That's an experiment you can't do on a day. 455 00:49:44,820 --> 00:49:48,960 So we have to have the Terminators come frequently. 456 00:49:49,620 --> 00:49:55,860 But that doesn't say anything about how fast or slow the sun rotates near its nuclear reactor. 457 00:49:56,190 --> 00:50:01,290 We don't know that. And so we were assuming well, maybe to say, yeah, why not? 458 00:50:01,680 --> 00:50:07,080 If we have to make an assumption, let's say it's the same. We still don't know that today. 459 00:50:08,250 --> 00:50:11,880 We know it's for a giant stars that are very far away in the galaxy. 460 00:50:12,180 --> 00:50:15,990 But we do not know it for our own sun. Why not? 461 00:50:16,200 --> 00:50:19,620 Because the quakes of the sun do not go deep enough. 462 00:50:20,110 --> 00:50:24,480 Remember I had this cartoon with this red and yellow and this green wave. 463 00:50:24,930 --> 00:50:29,940 And there was also a purple one that goes straight to the centre of the star. 464 00:50:30,180 --> 00:50:35,549 And I love purple waves because they probe the in the region of the sun. 465 00:50:35,550 --> 00:50:43,080 And that's where the life is directed. The sun may have such waves, but we have yet to detect them. 466 00:50:43,260 --> 00:50:50,420 They are blocked for the sun. More massive stars do have such purple waves and ridges also. 467 00:50:50,610 --> 00:50:55,830 And so we can use them to deduce the rotation and the mixing of the core. 468 00:50:56,400 --> 00:51:01,530 Right. So it's all a matter of getting to this in the region of a star. 469 00:51:01,770 --> 00:51:10,740 And this white area here is a is a cartoon to to imagine the parts of the star that take part in the nuclear fusion. 470 00:51:11,940 --> 00:51:18,780 And surrounding it is mixing going on and you see indicate that's here and then the radiation 471 00:51:18,780 --> 00:51:26,790 comes out the matter in this next area is something that determines how long the star can live. 472 00:51:27,060 --> 00:51:29,730 And this is very different for different types of stars. 473 00:51:30,420 --> 00:51:38,280 So we have been able now to measure somehow contributions of rotation to mixing tea with milk. 474 00:51:39,180 --> 00:51:44,520 Efficient mixing. Fast. Yeah. And that's what's going on in stars. 475 00:51:44,520 --> 00:51:53,190 And we need more. We found that there is more matter that can take part in the nuclear fusion than we had anticipated. 476 00:51:53,640 --> 00:52:01,590 So very massive stars that I haven't discussed very much so far will not only burn hydrogen and transform it into helium, 477 00:52:02,010 --> 00:52:10,410 then they contract and then they start burning helium and turn it into carbon and they build up the whole chemical table, so to speak. 478 00:52:11,850 --> 00:52:16,710 And the way they do that really depends on how the material is efficiently mixed. 479 00:52:17,250 --> 00:52:26,330 So we found recently that more helium is produced in the very stable, earliest phases of stars. 480 00:52:26,340 --> 00:52:36,960 And that's means that the chemistry that the universe is undergoing and the Milky Way in general may be different than we had anticipated before. 481 00:52:36,990 --> 00:52:40,410 So this is quite a recent fun. No. 482 00:52:41,160 --> 00:52:45,420 And that is thing we want to know is how far away are the stars. 483 00:52:45,810 --> 00:52:49,799 This is relevant for those of you who were in yesterday. 484 00:52:49,800 --> 00:52:54,800 We had a fascinating lecture on extraterrestrial life. 485 00:52:54,810 --> 00:53:03,060 And so quite often we get the question, tell us where to fly to another planet because it's not going very well here. 486 00:53:03,270 --> 00:53:10,350 Well, that's. I even had once received the question from somebody. 487 00:53:10,590 --> 00:53:15,840 You telling me the planets and I pay you money. Yeah. 488 00:53:16,680 --> 00:53:19,920 That's really the type of questions you get sometimes. 489 00:53:19,980 --> 00:53:26,490 So then I gave a whole lecture on how stars live and how their planets live along with the stuff. 490 00:53:26,910 --> 00:53:31,100 And so one of the things that then comes into play is how far away are stars? 491 00:53:31,200 --> 00:53:37,020 Again, this seems a simple question. Why is that so easy? Because you see them as point sources in the sky. 492 00:53:38,100 --> 00:53:44,940 Now, this requires that we are able to determine the intrinsic energy output of the star. 493 00:53:45,180 --> 00:53:46,169 Think of a lamp. 494 00:53:46,170 --> 00:53:55,740 You know, if you have a lamp and I put them at two metres from you, then if you experience a certain what we call luminosity strength of the light. 495 00:53:56,070 --> 00:54:01,020 But if I put it a kilometre further away, even if it shines intrinsically in the same way, 496 00:54:01,020 --> 00:54:10,230 you won't see it anymore because the distance to the star is really an important factor here, and stellar distances are not so easy to determine. 497 00:54:10,650 --> 00:54:17,340 So what do we need to do for that? Well, we can know the ages of stars now from seismology. 498 00:54:18,510 --> 00:54:22,920 And so if we know the radius and the temperature at the surface, 499 00:54:23,220 --> 00:54:29,070 then we know the intrinsic energy output at the stellar surface, and then we can derive the distance. 500 00:54:29,550 --> 00:54:33,480 And I call that a seismic distance because we use star quakes to derive that. 501 00:54:33,810 --> 00:54:35,750 And so then you can give a diagram. 502 00:54:35,760 --> 00:54:44,570 So people who study galaxies or our own Milky Way for the moment, the age of the star from the quakes as a function of the distance. 503 00:54:44,580 --> 00:54:50,000 And this is very far out in the galaxy. This is a result obtained from the coral satellites. 504 00:54:50,000 --> 00:54:58,770 So the European satellite that flew about ten years ago where each of these blue dots is a red giant 505 00:54:58,770 --> 00:55:06,210 star in our galaxy where the seismology has given us the H and we still have quite some uncertainty. 506 00:55:06,240 --> 00:55:10,670 You see that and the distance and the uncertainties are quite large, 507 00:55:10,680 --> 00:55:17,250 but you have to realise that before the coronation this diagram was empty, so to speak. 508 00:55:17,520 --> 00:55:26,580 Yeah. So this is really a major challenge, particularly if you think of how far these stars are. 509 00:55:26,850 --> 00:55:31,080 And we astronomers tend to express that in a unit called Parsec. 510 00:55:31,260 --> 00:55:38,220 Yeah, but I've written down for you. What that means is 31 and then 15 zeros if you express in kilometres. 511 00:55:38,720 --> 00:55:44,580 Yeah. That's very, very far away. And yet we can determine their ages. 512 00:55:44,760 --> 00:55:47,970 That's amazing. Thanks to the star eclipse. 513 00:55:48,750 --> 00:55:51,750 So where do we want to go with this domain? 514 00:55:51,780 --> 00:56:05,450 Well, it's really an interesting time, as we also heard yesterday, because we are really at the good time to start hunting for extra terrestrial life. 515 00:56:05,460 --> 00:56:14,100 What does that have to do with stars? A lot. Because planets are in orbits around host stars, as I call them. 516 00:56:14,100 --> 00:56:21,030 The Sun is our host star. And we can determine our ages of stars and sizes across their life. 517 00:56:21,480 --> 00:56:26,310 So the question then is will stars when they have planets? 518 00:56:28,950 --> 00:56:32,070 Will they have an ideal circumstance for life or not? 519 00:56:32,580 --> 00:56:41,970 Does the life stay there for a long time or not? When when the star starts expanding as a giant and, you know, burn the planet in general. 520 00:56:42,360 --> 00:56:49,050 So there are all sorts of interesting questions that couple planets around stars to their own. 521 00:56:50,010 --> 00:56:51,810 And we want to understand that better. 522 00:56:52,050 --> 00:57:00,810 And so ideally, you want to study exoplanets and measure their quakes, because then we have a good handle on this. 523 00:57:00,990 --> 00:57:06,569 And this is what the Kepler mission and the current mission used as a way to discover exoplanets. 524 00:57:06,570 --> 00:57:12,960 So this talk is not about exoplanets, but stars. But this is a star and in front of it passes are planets. 525 00:57:13,620 --> 00:57:20,070 And as we'll see moving on, how do we find these exoplanets efficiently nowadays? 526 00:57:20,520 --> 00:57:26,399 We can't see them. As I said in the beginning, because they don't they don't produce nuclear fusion. 527 00:57:26,400 --> 00:57:31,710 They can't do that. And so their brightness is mainly reflected light from their host star. 528 00:57:32,190 --> 00:57:36,960 But when a planet passes in front of its parent star, its host star, 529 00:57:37,170 --> 00:57:44,880 you see a tiny little dip in its brightness because you cover a part of the surface without being able of resolving the surface. 530 00:57:45,330 --> 00:57:52,800 You do see when you have a very high precision instrument that measures brightness variations, 531 00:57:53,100 --> 00:58:00,030 you do see a, you know, oh, there is an object passing in front of the star and in my line of sight. 532 00:58:00,660 --> 00:58:05,160 And so this dip here happens to be of older parts per million. 533 00:58:05,880 --> 00:58:14,520 So, in fact, people who study star quakes and who hunt for planets around other stars and the sun meet the same data. 534 00:58:14,850 --> 00:58:19,230 And that's why these two science cases go hand in hand. 535 00:58:19,860 --> 00:58:24,090 Of course I'm on this part. Yeah, others are on this part. 536 00:58:24,120 --> 00:58:32,100 But we work together to make this science case optimal because we have many planets. 537 00:58:32,130 --> 00:58:38,730 We heard that yesterday. We have thousands of planets discovered meanwhile, but we don't know how large they are. 538 00:58:38,730 --> 00:58:41,770 And we don't know what their ages. 539 00:58:41,790 --> 00:58:46,840 If we. Cannot have that information from their staff. 540 00:58:47,140 --> 00:58:52,600 And so that's where ostracism ology can help, and that's what we are doing in practice. 541 00:58:52,990 --> 00:58:59,200 So the Kepler mission mainly has given us many, many transits, detections of exoplanets. 542 00:58:59,290 --> 00:59:04,870 And here is one of their first ones. So we number them that's boring naming. 543 00:59:05,350 --> 00:59:08,410 But then so what do you do when you have a transit? 544 00:59:08,440 --> 00:59:14,080 Well, if you have the radius of the star, then you can deduce from the duration of the eclipse. 545 00:59:14,470 --> 00:59:18,820 The radius of the planets. Yeah. And we can do that from the transits. 546 00:59:19,960 --> 00:59:27,430 Then you need the radius of the star with a very high precision and quakes give you an extremely high precision compared to any other. 547 00:59:28,120 --> 00:59:36,100 So that's one thing. But then we also want to know, is this a planet where it would be nice to live or not? 548 00:59:37,180 --> 00:59:44,830 Is it a gaseous planet or a rocky planet? You could say, yeah, because on Jupiter we would not want to go and live Slap Pleasant there. 549 00:59:45,220 --> 00:59:52,780 So when we think of life as we know it on Earth, you want to know as a first rough estimate the density of the planets. 550 00:59:53,290 --> 00:59:56,110 And so how do you get a density if you have the size? 551 00:59:56,140 --> 01:00:05,560 You also need to know the mass, because then we can compute the average density by dividing the mass by the volume of the planet. 552 01:00:06,070 --> 01:00:09,820 And so for the mass, we must rely on data from the ground. 553 01:00:10,030 --> 01:00:18,970 I love this this synergy between space and ground based data, because this is really very powerful in this time. 554 01:00:19,400 --> 01:00:22,480 And so how do we do stellar masses? Well, you have a star. 555 01:00:22,630 --> 01:00:27,820 You have planets going around it, and they are in each other's gravitational field. 556 01:00:28,090 --> 01:00:33,190 So the whole star is wobbling because there is a planet circling it. 557 01:00:33,200 --> 01:00:42,670 Right. And we also make the sun wobble. But the mass of the earth versus the sun is so very different that this wobble is very tiny. 558 01:00:43,030 --> 01:00:46,090 So you need a very accurate velocity metre. 559 01:00:46,450 --> 01:00:50,650 But we can do that in ground based observatories nowadays. 560 01:00:50,920 --> 01:01:01,000 And so here you see the wobble of the star Kepler that has a planet can be because of the planet that's going around. 561 01:01:01,420 --> 01:01:09,370 And so from Johannes Kepler, we then know how to compute the ratio of the masses. 562 01:01:09,540 --> 01:01:19,450 And so in that way, we can get the mass of the planets divided by the volume from seismology and from this transits duration. 563 01:01:19,660 --> 01:01:26,830 And then we get a density. And for this planet, it is 8.8 grams per cubic centimetre. 564 01:01:27,190 --> 01:01:34,720 Yeah. Would that be a Jupiter type planets or would that be an earth like planets? 565 01:01:36,250 --> 01:01:46,260 What's the average density of our earth? It's about five. 566 01:01:46,530 --> 01:01:52,540 Yes. Again, a typical question that's a non astrophysicist audience would like you. 567 01:01:52,590 --> 01:01:58,300 I never thought about that. So here are some numbers. 568 01:01:58,740 --> 01:02:02,370 So from this, we know that this is a rocky planet. 569 01:02:02,370 --> 01:02:07,620 And that's why it made this press release, because it was one of the first ones that the Kepler mission could detect. 570 01:02:08,010 --> 01:02:11,580 Okay. Now, where are we heading for? 571 01:02:11,820 --> 01:02:15,960 I have two projects in the near future that are very interesting for the science case. 572 01:02:16,290 --> 01:02:20,610 And one is the the first mission. That's another mission. 573 01:02:20,760 --> 01:02:26,729 And it's going to do an all sky survey with the aim to find planets around stars. 574 01:02:26,730 --> 01:02:31,610 But it's going to find big gaseous planes in nearby orbits around hosts. 575 01:02:31,800 --> 01:02:36,210 So not planets. Interesting to search for habitable life. 576 01:02:36,720 --> 01:02:43,230 But the other mission that we are very fond of here in Europe is the so-called Plato mission. 577 01:02:43,230 --> 01:02:51,389 Plato is a mission that is designed to do is to assess mythology of stars and hunt for planets like the Earth in low orbits, 578 01:02:51,390 --> 01:02:53,550 like one year orbits, like where we are. 579 01:02:53,940 --> 01:03:01,440 And to see if we can study these planets with yet other missions that are not yet approved, but certainly under development. 580 01:03:01,710 --> 01:03:11,610 And we hope that they will then also make it then we are past 2030 because Plato will do that for nearby stars, much nearby than Kepler. 581 01:03:11,820 --> 01:03:21,810 And then we can hope to estimate even the the habitability of the planets from infrared spectroscopy that's further down the line. 582 01:03:21,840 --> 01:03:25,500 Then I'm retired, so somebody else will. 583 01:03:25,980 --> 01:03:35,220 We'll take that up. I'm sure it will happen. And to round off and give you an idea, we know many, many exoplanets around very interesting stars. 584 01:03:35,580 --> 01:03:38,639 The closest one is our closest neighbour. 585 01:03:38,640 --> 01:03:46,950 And I've written down here the distance because these rich persons who ask me to give up planets when they see this, 586 01:03:46,950 --> 01:03:50,130 then somehow they come to reality. 587 01:03:50,370 --> 01:03:59,480 And that is important for me to realise because it is telling us how precious we should be for our own. 588 01:03:59,840 --> 01:04:04,950 Yeah. So the best cases of these extrasolar planets found so far. 589 01:04:05,310 --> 01:04:10,790 I couldn't even pronounce this number in English. Sorry. That's only my third language. 590 01:04:10,800 --> 01:04:16,930 And it's difficult to do big numbers in languages that are not their mother tongue. 591 01:04:17,160 --> 01:04:21,420 Mars is about this distance. Just to give you an idea, we can fly to Mars. 592 01:04:21,420 --> 01:04:23,220 We can do that. We can bring you there. 593 01:04:23,640 --> 01:04:31,740 So the closest planets with current rocket technology and without underestimating our engineers, it would take us 100,000 years. 594 01:04:31,770 --> 01:04:37,409 Not very practical. Okay, so why am I ending like this? 595 01:04:37,410 --> 01:04:41,400 Because I find it really important that we realise that, you know, 596 01:04:41,430 --> 01:04:47,200 it's not going to be like in this cartoon, you know, if we screw up here, then we really have a problem. 597 01:04:47,230 --> 01:04:52,590 So even if there are copies of the Earth, we're not going to go there immediately. 598 01:04:52,800 --> 01:04:57,720 And we should really take care of our planet because it's not going to be like this. 599 01:04:58,080 --> 01:05:05,610 And with that, I'd like to end with much gratitude so that I can explain fundamental science to a broad audience, 600 01:05:05,610 --> 01:05:08,850 which is one of my favourite activities. Thanks.