- il y a 2 jours
In this course we will discuss the formation of stars and planets. We will explain the, sometimes violent, processes that occur during their formation and explain how the combination of theory and observation have led to our modern insights. Data from state-of-the-art telescopes will be presented and their impact on our current understanding will be discussed.
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ÉducationTranscription
00:00:00Thank you very much. Can you hear me? Okay. Fantastic.
00:00:04Well, welcome to the course with the Observatoire Royale de Belgique, The Koninklijke Sterrenwacht in België, or even the Royal Reserve in België.
00:00:29And Thibault asked him to talk a little bit about star and planets formation to you, and he gave me five hours for that.
00:00:39And then I thought, well, star formation can take thousands of years. How do I do this in five hours?
00:00:46But then I thought, ah, but I taught star and planets formation at university in the United Kingdom, where I work, and it was 21 lectures, 21 hours.
00:00:56And then I thought, well, hang on. I've got the course that's 20 hours.
00:01:01But that's for 30 years students at university in the United Kingdom.
00:01:05And here I'm talking to the good people of Drussels. I can do exactly the same, just for the five hours.
00:01:10So that's what we're going to do. No, I'm kidding. All the equations are left out. That's a big part of it.
00:01:19So I thought, why don't I just tell you a little bit about me, because you will be looking at me for five hours.
00:01:26So my name is Helene Ausmein. I did my PhD in Groningen in the Netherlands, in the north.
00:01:34It is in the north of the Netherlands, and some of my colleagues here in Drussels asked me whether we could see the northern lights.
00:01:40But it's not that north, it's the Netherlands. Then I moved to London, where I took up a position as a post-doctor.
00:01:49That's a very strange job title, really. But it means post-doctoral. So that's a job that you do after you become a doctor, after you doctorate.
00:01:58And after that, I got a job in Leeds, in the north of England. Also didn't see the northern lights there.
00:02:06I was there until last year. I moved to the Royal Observatory, where I am currently, and hopefully this works,
00:02:16not the clicker, otherwise I have to work all the time.
00:02:20Well, I need you now, Thibaut, because I can't even go to the next thing.
00:02:26Okay, so this computer also stopped. Doesn't matter if Thibaut comes back.
00:02:34And if you notice, then tell me.
00:02:37And since last year, I'm here at the Royal Observatory, where I am both the senior scientists,
00:02:43and I'm the head of communication. And one of the big things that we are doing
00:02:47is organizing the celebrations we will have for our 200th anniversary next year.
00:02:54So the Royal Observatory is older than Belgium. But that was named Royal a little bit later.
00:03:01And Thibaut is talking that these lecture courses here have been instigated by the very first director of the Royal Observatory, Adolf Kutteler.
00:03:12So it's really nice to follow up in that order.
00:03:19Now, so still not Thibaut. My next slide is basically I wanted to tell you a little bit about the next five hours.
00:03:29And I thought it might be a good idea to give an overview in this first hour.
00:03:37Ah, specialist?
00:03:38No, no, I'm helping Thibaut sometime.
00:03:41Okay, you can check it.
00:03:43It doesn't.
00:03:45And the first day, I'd like to give you a little bit of an overview.
00:03:49Well, that information started from the beginning and all the way to stars and planets and form.
00:03:55And then I selected some topics that I hope you might find interesting.
00:03:59So next week, the story will be the violent processes that actually take place during the formation of a star.
00:04:08And while I did.
00:04:38Today, in 2021, about 2025, the problems that we're facing with presentations and with scientific questions.
00:04:50The week after, I thought it would be nice to give you an update on what we know of planets, how they form and what they are and how we detect them.
00:04:59And I'd like to conclude the course by looking at the future.
00:05:04One of the things that I'm actively working on is the next big telescope around.
00:05:10And it's a telescope.
00:05:12The biggest optical telescopes we have are about 10 meters across.
00:05:17And the next generation big telescope will be 39 meters.
00:05:22I don't know how big this room is.
00:05:24It's probably something like that.
00:05:25And we call that the extremely large telescope.
00:05:29Because astronomers are not very good in names.
00:05:33Okay, let's just hope.
00:05:36So I got, yes.
00:05:39So that one we hadn't seen.
00:05:41So I'm working in Brussels.
00:05:43And today's the overview.
00:05:46Next of star formation and the jets, I want to talk about massive stars, planets and the future.
00:05:54So there you go.
00:05:55You didn't miss anything apart from this beautiful image of an object that's called Sharpless 106.
00:06:02Simply because Mr. or Dr. Sharpless cataloged some nice nebulae and this is number 106.
00:06:11And the topics that would be nice to talk about today are some questions that you may have or perhaps not.
00:06:19But why is the star round, for example?
00:06:23And why do I want to talk about it when I'm talking about star formation?
00:06:28Another question is why can we see young stars when we have x-rays?
00:06:35Have you thought about it, right?
00:06:38Why, when you think about this, we have the solar system and all the planets are in one plane?
00:06:44Why?
00:06:46Why pizza?
00:06:49I'll tell you.
00:06:51And so, but I thought it would be nice to actually get a little bit of an inventory of our own solar system.
00:06:58And what better place to start than here in this lecture theater.
00:07:02So let's zoom out.
00:07:04And here we can see Brussels.
00:07:07And after five minutes, I found us.
00:07:09We're here.
00:07:10Let's zoom out a little bit more.
00:07:13And after 10 minutes, I found out that we're here.
00:07:18Let's zoom out a little bit more.
00:07:20And now I don't have these orange crosses anymore, but this is the famous Earth rise.
00:07:25That was a picture taken 50 years ago from the Moon.
00:07:30Let's move out a little bit more.
00:07:33And then we see a beautiful Earth and Moon system.
00:07:37And the first time I showed this picture on the screen, I really knew, saw this, right?
00:07:43This is quite flat.
00:07:45So the flat Earth conspiracy people were half right.
00:07:50Right?
00:07:51It's flat.
00:07:52So, but I think in reality, of course, the sun is shining and we get half the Earth and half Moon.
00:08:00Okay, let's zoom out a little bit more.
00:08:03And this is a picture that was taken by one of the probes that we sent into space.
00:08:08This is in 2013.
00:08:10And this is the day the Earth smiled because the satellite had moved from the Earth past Saturn and looked back.
00:08:19So it's looking back.
00:08:20So it's looking back.
00:08:21So this part of Saturn is dark.
00:08:22Okay?
00:08:23And, yeah, if you want to look closely, you might even see the Earth.
00:08:32Okay?
00:08:33I can see it.
00:08:34I can see it from here.
00:08:35But let me just zoom in a little bit.
00:08:38That's us.
00:08:40But that gives you already an indication how big the solar system is.
00:08:45This is us, right?
00:08:47And I can become very philosophical and melodramatic about it.
00:08:51But a very famous astronomer, Carl Sagan, already did it for me.
00:08:56And he calls the Earth the blue dot.
00:08:58Everybody we know, everybody who's lived, et cetera, et cetera, was there.
00:09:02Okay.
00:09:03So that's as far as the pictures I could get.
00:09:08But just to get a little bit more of a feel of our own solar system, I've got all the planets that we know to scale here.
00:09:16So we start with the Sun, the Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
00:09:25And the distances are not to scale, but the sizes are.
00:09:28Okay?
00:09:29So you can see that Earth and Venus are almost equally big.
00:09:33But Earth is much bigger than Mars.
00:09:35Jupiter is the biggest.
00:09:37And, of course, the Sun is the biggest.
00:09:40Some of you, not many, because it's quite a young audience here, would think that we might have a ninth planet.
00:09:48But Pluto used to be known as a planet up until 15 years ago.
00:09:55And then we started finding a lot of small planets like Pluto.
00:10:00And people said, okay, that's it.
00:10:02Do we call these new bodies planets or shall we use a new class of objects?
00:10:08And so people started talking about dwarf planets.
00:10:12We knew about Sirius, which is in the asteroid belt.
00:10:16And I found a couple of more then.
00:10:18And they said, okay, we demote Pluto and make it a dwarf planet.
00:10:22So we've got eight planets, big ones, and quite a few smaller bodies in the solar system.
00:10:30Okay, so this gives you an idea of the sizes of the planets.
00:10:34Let's have a look at the size of the solar system.
00:10:38So here I've got the inner solar system.
00:10:41We've got the Sun in the middle, Mercury, Venus, Earth, and Mars.
00:10:46Then we've got the asteroid belt.
00:10:48And I show you Jupiter here.
00:10:50So you can see that Jupiter is quite far away from the Sun already.
00:10:55And the distance between the Earth and the Sun is what we call one astronomical unit.
00:11:02Unité astronomique.
00:11:06And the distance between Jupiter and the Sun is five astronomical units.
00:11:13Okay.
00:11:14And the Earth turns around the Sun in one year.
00:11:17And Jupiter does it in 12 and a half years.
00:11:22Okay.
00:11:23So in the inner parts of the solar system, they orbit much quicker than in the outer part, than further out.
00:11:30So let's zoom out a little bit more.
00:11:32So I've got this square here, everything with Jupiter.
00:11:36And then we've got Saturn, Uranus, Neptune.
00:11:39And to guide the eye, I've got Pluto as well.
00:11:43But you can see already that the solar system is quite big.
00:11:48If this is about 5 AU, then 10, 15, 20, 20, 30 AU.
00:11:55It's quite big.
00:11:56And here, I put in an object that's called Sedna.
00:12:00That object is really far away from the Sun.
00:12:05And it's, therefore, very dark.
00:12:08There's not a lot of sunlight that's falling onto that object.
00:12:12And it doesn't reflect a lot, because we can see the Moon.
00:12:15I don't know whether you saw the Moon tonight, but it's pretty bright.
00:12:18And there's all sunlight that's being reflected.
00:12:21Well, but the further away you are from the Sun, the less you have.
00:12:24So this object is very dark, and therefore very faint, and therefore very difficult to see.
00:12:31And that's the reason we astronomers only discovered it 20, 30 years ago.
00:12:37Okay?
00:12:38And that tells you already that there must be many more there that we don't know about.
00:12:43But I want to, oh yeah, and this is the other thing I forgot almost to mention.
00:12:47We've got an asteroid belt here.
00:12:50But further out, we even have something that's called the Kuiper belt, named after the Dutch astronomer Kuiper,
00:12:59where we found there's quite a lot of asteroid comet-like bodies as well.
00:13:04Okay?
00:13:05And then we've got Setna.
00:13:07Let's zoom out, because after a couple of years of observing, we know the orbit of Setna.
00:13:15And that's pretty big.
00:13:18Okay?
00:13:19And I think one orbit of Setna takes about 20,000 years.
00:13:26And I think 10,000 years from now, when it's here, it will be very well.
00:13:32If it would have been here, it would be invisible for us, simply because it's so far away from the Sun.
00:13:38But see, this little box, and then that box is here where my finger is, just to give you an idea about how big the solar system is.
00:13:48So let's zoom out a little bit more.
00:13:50And then we find at tens of thousands of astronomical units the so-called Oort cloud, which is a reservoir of comets.
00:14:00And we know it's there because whenever a comet is coming towards us, we can work out where it's coming from.
00:14:07And it's this Oort cloud.
00:14:12There's another comet in the news now.
00:14:14It's called 3I Atlas.
00:14:17The I stands for interstellar, because it's got such an orbit, it doesn't come from anywhere in the solar system.
00:14:23It's coming from far away, so it's interstellar.
00:14:28But this is essentially our solar system.
00:14:33And in a nutshell, in a pretty flattish region, we've got all the planets and the Kuiper belt.
00:14:42And the size is about 150 astronomical units.
00:14:47Okay.
00:14:48And this Oort cloud, it's not flat.
00:14:52It's roundish.
00:14:54And it extends to about 100,000 AU.
00:14:58And if I would look at interstellar space, the next star is essentially where the table is.
00:15:05So the extent that the size of the solar system is really big and it fills up a lot of space.
00:15:12Okay.
00:15:13And this, the star and planet formation course and the research that we're doing is aimed to understand where did this come from?
00:15:25Right.
00:15:26And the next question is, of course, where do we come from?
00:15:29And the other question is, are we alone, et cetera?
00:15:32So, but I just now gave you a little bit of the inventory.
00:15:37And the questions that we like to first ask and answer are, we've got small rocky planets close to the star.
00:15:47How do I end up with small rocky planets close to the star?
00:15:51I don't think I mentioned rocky, but if I'm talking about Mercury, Venus, Earth and Mars, they're very small, but they're very dense.
00:16:00It's basically made out of rock.
00:16:02Okay.
00:16:03If I go to Jupiter and Saturn, they're very big.
00:16:07And they mostly consist of gas, a very dense atmosphere.
00:16:12And that's why we call them gas giants.
00:16:15Gas because of the gas, giant because the big.
00:16:18Right.
00:16:19Giant gazeuses.
00:16:21So we've got these gas giant planets further away.
00:16:24We'd like to be able to explain that.
00:16:27Then we've got a flat structure, almost like a pizza, going to about hundreds of astronomical units.
00:16:36And then this rounder structure going all the way to almost the next star.
00:16:42So these are the questions, the basic fundamental questions that we'd like to answer in studies like star and planet formation.
00:16:51Okay.
00:16:52And in the next hopefully half an hour, I will give you an overview of that.
00:16:57And probably we'll be finishing by saying that we don't know everything and that we've got some things horribly wrong.
00:17:04Okay.
00:17:05But that's the thing about research.
00:17:08Now, I'd like to start them with a star.
00:17:12And I'm only going to ask you a few questions today.
00:17:17But perhaps someone could tell me, what is a star?
00:17:22What is a star, really, when you think about this?
00:17:25I'm talking about stars and planets.
00:17:27But what's a star?
00:17:29What's different from a star than a planet or my pointer here?
00:17:33What's a star?
00:17:34What's a star?
00:17:35What's a star?
00:17:36Does anybody have an idea?
00:17:40Yes.
00:17:41Fantastic.
00:17:42It's absolutely, it's a ball of gas.
00:17:47And it's mostly made out of hydrogen and helium.
00:17:54And it's burning hydrogen in the center.
00:18:00Okay.
00:18:01And that hydrogen is essentially being converted by nuclear fusion into helium.
00:18:07So, it's not burning, burning, but that's the word that we use for that.
00:18:11Okay.
00:18:12And so, there you go.
00:18:14It's a hot bowl of gas with the furnace in the center.
00:18:17And that furnace is your nuclear fusion.
00:18:20And when you think about this, we know about it.
00:18:23We've seen that before.
00:18:25Here, I've got myself a hot air balloon, right?
00:18:29And normally, that balloon is just flat.
00:18:33But when I turn up the fire, the air expands, gets lighter, and the balloon lifts off, right?
00:18:43And then, I've got another question, because I'm not asking, don't worry.
00:18:49But the reason that that gas that wants to expand because it gets hotter, the molecules start moving faster.
00:18:56But it's the balloon that actually keeps it all together.
00:19:01It's the tension of the balloon that's actually fighting that hot gas that wants to expand, right?
00:19:10Well, I don't have a balloon around the sun.
00:19:15So, I've got hot gas.
00:19:16It wants to expand, just like the gas here.
00:19:20But the same, good.
00:19:25Does anybody know what could fight that thermal pressure that wants to make that star to some bigger?
00:19:35Yeah.
00:19:37Gravity, indeed.
00:19:39It's a fight, in this case, between the thermal pressure outwards and gravity that's holding it all together.
00:19:47And it's a very delicate balance, okay?
00:19:51And now, you start perhaps, you can understand why the sun is round, because gravity becomes less with distance.
00:20:00But it doesn't matter in what direction I go, that force is always the same.
00:20:06So, that equilibrium between gas pressure on the one hand and gravity on the other hand is the same everywhere as well.
00:20:13And that's why the star is round, okay?
00:20:16But the thing is, there's this fight all the time between a force going out and a force going in.
00:20:28And the sun stays the same, because at this moment in time, they're equal.
00:20:33At least they're equal here.
00:20:37And if I now move out to other parts in the universe, I've got the same thing.
00:20:45Here, I've got a very weird thing, which we call a molecular cloud, okay?
00:20:55The first time such a dark cloud was discovered was by William Herschel a couple of hundred years ago.
00:21:04And he saw stars, and suddenly a hole in the sky.
00:21:11And he didn't know what he was looking at.
00:21:13He said, oh my God, German.
00:21:16There's a hole in the sky.
00:21:19And for many years, people thought, oh my God, that's just empty, devoid of stars.
00:21:23But if you now look closely, we see white stars here, white stars here, nothing, and red stars, right?
00:21:35Now, it would be really a coincidence that only the stars very close to this cloud would be red.
00:21:44But instead, imagine now that all the stars here in the neighborhood are white.
00:21:50And I put some material in front of it, just like my hand, that's blocking the light, okay?
00:21:57Now, if I have my hands in front of it, then all the light is blocked.
00:22:05But if I cut small particles, small dust particles, dust particles basically almost like cigarette smoke.
00:22:13Then we find that blue light is stopped, but red light is stopped a little bit less, okay?
00:22:23And that's what we see.
00:22:24And here we've got so much material that all the light is blocked.
00:22:27But here we can actually see that the red light is shining through.
00:22:30And if you look closely, you go from red to orangeish, yellowish to white.
00:22:37And it turns out that that simple fact that if something, in my case, my hand, is larger than the wavelength of the light, it will be blocked.
00:22:50If my hand is smaller than the wavelength of the light, like radio waves, it will go straight through.
00:22:57And the fact that we still see some red light here gives us immediately an idea how big these particles are that I find in that molecular cloud.
00:23:07Okay?
00:23:08And then I can work out how much do I need to block all that light.
00:23:14And then we find that this molecular cloud, because there's also molecules, is so big that we can form perhaps even one, two, three, or even ten stars.
00:23:26It's that massive.
00:23:29So, that's one thing.
00:23:31And the other thing is, this is, it's really a cloud, because I've got all these particles moving about.
00:23:39They also, it's very cold, but they still move.
00:23:43And they also want to go out, but the gravity of that cloud is still holding it together.
00:23:50But it's a very, very delicate balance.
00:23:53And let me see what I've got a pen, because this is a very fragile balance as well.
00:24:00And it only needs a little bit of perturbation, and something can happen.
00:24:06Now, my pen is completely symmetric.
00:24:10There is really no reason why it should fall over if I place it properly here on the ground.
00:24:16But I have to be very precise.
00:24:20And nothing should perturb it, right?
00:24:22And I can prove until now already, it will be about 0.1 second, and it will fall over.
00:24:29Right?
00:24:30But nothing would have stopped it from staying put.
00:24:32But it doesn't.
00:24:33Because it's a very delicate balance.
00:24:36And we've got the same delicate balance in such a cloud.
00:24:40Yeah, I know what happened.
00:24:47Put my microphone in my bag, which is not something that you should do.
00:24:55Let's have a look.
00:24:57So, we now found that hole in the sky, but we found more and more and more of these molecular clouds.
00:25:06And even if I go to other galaxies, I find it.
00:25:11Yeah, this is, I think, just a beautiful picture anyway.
00:25:14But what we see is just a spiral galaxy.
00:25:18So, you've got the center.
00:25:20You've got the spiral arms.
00:25:22And what you notice is that there's a lot of black here.
00:25:26And this is all molecular clouds, just like I showed you.
00:25:31They are big.
00:25:32We call them giant.
00:25:33And there's another thing that you notice, that the stars here are bluish.
00:25:39And the star here are yellow.
00:25:44And then we've got some red smudges.
00:25:46And I will tell you everything about it next week.
00:25:49But blue stars, we found, and this is what we teach in our very first lecture at university, are massive stars.
00:26:00They're very hot, very massive.
00:26:03And massive stars don't live very long, okay?
00:26:08Yellow stars, like the sun, they can live for billions of years.
00:26:13Blue stars, millions of years.
00:26:16But if they don't live very long, they don't move very far either.
00:26:21And are often found very close to where they were born.
00:26:25And what we find very often is that young stars are always very close to these molecular clouds.
00:26:34So that gave us a little bit of an observational evidence that these dark clouds, that are very massive.
00:26:42I just told you that I can form stars out of them.
00:26:45But young stars are often found there as well.
00:26:48And sometimes when we look in detail at these clouds, this is not a cloud.
00:26:55We find some very strange objects inside there.
00:27:00I think this one is called the Australia Nebula, probably because it looks a little bit like Australia.
00:27:09And this is an optical image.
00:27:12So the cloud, the dust in that cloud is blocking optical light.
00:27:18But if when I would go to longer wavelengths like infrared, I would be able to see through the dust.
00:27:26And that's what I'm doing on my next slide.
00:27:29Here, I'm looking at data from 2003 from the Spitzer telescope at infrared wavelengths.
00:27:38So this is what we just looked at, the molecular cloud and the thing inside it.
00:27:43Now we see through the dust.
00:27:45And look at this.
00:27:47There's a very strange object, which looks like something is shooting out on both sides.
00:27:54We call these jets, okay?
00:27:58And what we now think, well, what we now know, that's a young star, okay?
00:28:04So we found massive stars very close to these molecular clouds.
00:28:08And inside some of those molecular clouds, we find these very weird objects that are young.
00:28:14Now, you may have heard of the James Webb telescope.
00:28:20That's a six and a half meter telescope that's now in the sky.
00:28:24Looked at the same part of the sky, but 20 years later.
00:28:30So I just want to show you the difference between the noughties, 2003, and now.
00:28:36So this is now what the James Webb telescope shows us at infrared wavelengths.
00:28:41And I think this is quite pretty.
00:28:43Look at these two stars, these two stars, right?
00:28:46And then you've got the jets here.
00:28:48You see them here.
00:28:49So we have the observational evidence, if you like, that these clouds might actually, the cradles, the birthplaces of stars.
00:29:04And, yeah, so what can happen?
00:29:06And I just mentioned that this is a very fragile balance between the gas, dust, and the molecules wanting to go out and gravity wanting to put it in, okay?
00:29:19But it only needs a perturbation.
00:29:22It could be me giving basically a slap to give gravity a little bit of help, okay?
00:29:30And if gravity would win after a perturbation or anything that you can think of, supernova shockwave, that cloud can shrink, okay?
00:29:40And people thought about that idea quite a long time already, but someone called Jeans, hence my clothes, thought about it 100 years ago and worked it out.
00:29:50And he said, okay, what is the critical mass of such a cloud?
00:29:55Is it massive enough to actually shrink, to collapse into a star?
00:29:59And he found that, yes, if I give gravity a little bit of help in the beginning, I can actually have this cloud collapse and basically shrink.
00:30:10And essentially what we're talking about is that if I have such a collapsing cloud, I start off with something,
00:30:19it could be 10,000 astronomical units, and it's shrinking, it's getting denser, it's getting denser, it's getting denser, it's getting denser.
00:30:26It can get denser by perhaps even 10 to the power 21 times, one with 21 zeros.
00:30:36But when you think about this, if you think of the notion of such a cloud shrinking, a gas compressing, then if I compress a gas, what happens to the gas if I compress it?
00:30:53So I know you know it, so just say it.
00:30:56It's getting hotter.
00:30:57So it not only gets denser, but it gets hotter and denser and hotter and denser and hotter.
00:31:02And at some point it's so dense and so hot that hydrogen nuclei can merge together and form helium.
00:31:10So built in is the expectation already that indeed such a collapsing cloud could give me a star.
00:31:18So star is born.
00:31:23And then I've got something else that I'd like to share with you.
00:31:28Because if I suddenly I've got that cloud and I form a star, it shrinks, then there's still some stuff left that's falling onto the star.
00:31:38Okay.
00:31:39And then you can ask yourself, would we be able to see that?
00:31:45So if I've got myself a chalk here, and if I drop it, then you will hear a sound, I think.
00:31:55That's not a lot.
00:31:57Let's throw it there.
00:32:01So that was a little bit louder, but you catch the drift.
00:32:06Essentially, the noise, the sound that the chalk made, that's energy, that you need energy to make sound.
00:32:14And it was actually the gravitational potential energy that I released.
00:32:20So you can well imagine that if I drop something from very far, more energy will be released.
00:32:27And that's what my little assistant, this is a picture.
00:32:32I think it's 40 years old.
00:32:34So this is probably, this boy may be even retired by now.
00:32:38But, and he's American because this is a Fahrenheit.
00:32:41But this is an infrared image, so you can see that the boy is quite warm, and the ball he has in his hand is quite cold.
00:32:51And he basically dropped it a few times.
00:32:54And then you see that simply by dropping the ball, it became hotter.
00:33:01Essentially, the ball bounced on the floor, and that energy was converted, and it became hot.
00:33:07So that's another illustration that if something falls, that energy is being released.
00:33:16And if you just work out the numbers.
00:33:19If I would throw something from far away to a star, the temperatures in this case, it went from, I don't know, 70 something to 80 something Fahrenheit.
00:33:34But if I work out the numbers, if I throw something from very far onto a star, the energy that is released, it would mean that that material could be as hot as a million degrees.
00:33:46So I could probably see that if I would be sensitive to light that traces one million degrees.
00:33:55Okay.
00:33:56Now, if I look at a star or anything, a red star is red hot.
00:34:08And red hot is cooler than blue hot.
00:34:12So if something gets hotter, it emits at shorter and shorter and shorter wavelengths.
00:34:19And if something is a million degrees, I probably will see it at X-rays.
00:34:27Okay.
00:34:28Now then, let's have a look here.
00:34:31Here, I've got another picture of one of these molecular clouds.
00:34:37This is Messier 16.
00:34:40I think at some point they call this the pillars of creation.
00:34:44So it looks like pillars and stars are being formed.
00:34:47So this is Hubble.
00:34:49And people also have manufactured telescopes that operated X-rays.
00:34:55And Chandra is one of them.
00:34:58And if I look at exactly the same region, I could see that a lot of stars light up.
00:35:05And these are all young stars that are undergoing actually the accretion of material onto the surface.
00:35:13So with X-rays, I actually can identify young stars.
00:35:19It's amazing, isn't it?
00:35:21So then I wanted to show James Webb as well.
00:35:25So with James Webb, you can see through the dust a little bit more.
00:35:29And the next one, I think, is just very pretty.
00:35:32It's both the X-rays and the optical and James Webb.
00:35:37Okay.
00:35:38So we made a link between molecular clouds.
00:35:43We saw that we can form stars there if we've got enough material.
00:35:48We predicted that the gas gets hotter and denser so that we might actually get fusion.
00:35:54Then by throwing just some chalk on the floor, we predicted that we might even get X-rays.
00:36:00And we see them.
00:36:02So what else could happen with such a collapsing cloud?
00:36:09And it turns out that everything in the universe rotates.
00:36:16The Earth is spinning around its own axis one day.
00:36:20It takes one year to orbit the Sun.
00:36:23And even the Sun doesn't have a fixed location in the galaxy.
00:36:28It takes about 200 million years for the Sun to orbit the center of the galaxy.
00:36:35So even galaxies rotate.
00:36:37Or 200 million years.
00:36:39So one galactic year ago, there was a dinosaur talking to you.
00:36:44And you would all be dinosaurs as well.
00:36:46So there you go.
00:36:47But everything rotates.
00:36:49And so do these small clouds.
00:36:52These clouds.
00:36:53And they rotate ever so slowly.
00:36:56Okay.
00:36:57A cloud like this could take thousands if not millions of years to rotate.
00:37:02But it does.
00:37:03But now, I just told you that this cloud is collapsing and getting smaller.
00:37:10So it started off rotating slowly.
00:37:14But it gets smaller.
00:37:16It might actually rotate quicker.
00:37:19Okay.
00:37:20And let's look for another real life example where that happens.
00:37:29So here I've got a figure skater who's basically spinning.
00:37:37She's very big and makes herself very small.
00:37:40And rotates quicker, right?
00:37:41Then she goes up slower.
00:37:43And now, really quick.
00:37:46And I think the record is about 100 rotations per minute or second or something.
00:37:51I'm very, very quick.
00:37:52So that's a very well-known law.
00:37:56In physics, it's the conservation of angular momentum.
00:38:00Okay.
00:38:01So when I've got this cloud that's shrinking, it's not only getting denser and hotter.
00:38:07It also starts to spin faster.
00:38:09Okay.
00:38:10And then there's something else that we all know about, which results in the beginnings of a solar system.
00:38:21And I needed to get a friend of mine demonstrating this because I can't.
00:38:30But the principle that my pizza baker is going to show you is exactly the same reason why your clothes get dry in your washing machine when you spin it.
00:38:44Right?
00:38:45So you wash your clothes.
00:38:46They're wet.
00:38:47Then the drum starts to spin.
00:38:50And they get dry.
00:38:52Because the water is going outside through the holes, but your clothes stay put.
00:38:58If something spins, there is a centrifugal force.
00:39:02Something goes out.
00:39:04So I've got now this cloud that's rotating very, that's spinning very quickly.
00:39:09And it's almost like what my good friend here shows you.
00:39:13How do you get a nice pizza?
00:39:15Well, you spin it.
00:39:18And he's telling you that now in whatever language you're speaking.
00:39:22But basically by spinning it, it gets bigger.
00:39:29And if you don't believe me, just go to the next pizza restaurant.
00:39:32They do it for you.
00:39:33On YouTube, they've got quite a few interesting movies as well.
00:39:37So what I'm now actually predicted with you and discussed is that if I start with this molecular cloud that's shrinking and getting denser and spinning faster, I not only get a star in the middle, but a lot of stuff is expanding like a pizza.
00:39:55And if I make a pizza, it's always very clumpy.
00:40:00So if nature is as bad in pizzas as me, perhaps these clumps could be planets, but that's a different story.
00:40:08So in a nutshell, what I told you in the last half an hour or so, people put all the physics in a computer program to see whether they could form a star.
00:40:22Okay.
00:40:23And this is from a colleague in Australia.
00:40:27And he started off, he said, okay, I just start some very basic physics.
00:40:32There's a lot more to it than what I'm showing you now, but it gives you an idea.
00:40:36And he starts off with just a ball of gas.
00:40:40He just put it in computer and then he pressed return and let gravity do its thing.
00:40:45It's the same cloud that I'm looking at.
00:40:49One of them is a top view and one of them is a side view.
00:40:54And this is a zoom in of the middle.
00:40:57Okay.
00:40:58And I'll run it first one time and then I'll do it another time.
00:41:01If I can find the play, here's the play.
00:41:05So there you go.
00:41:07Essentially, you can see already that something is moving.
00:41:11It's shrinking.
00:41:12It's getting denser.
00:41:14This is the top view.
00:41:15You can see it's rotating very quickly.
00:41:17This is the side view.
00:41:19You see that we've got a pizza.
00:41:22And in this case, I actually form two stars.
00:41:26Okay.
00:41:27I run it again now that you're used to the idea.
00:41:30So this is the cloud.
00:41:31This is the top view.
00:41:33The side view.
00:41:34Zoom in.
00:41:35Okay.
00:41:36Let's see.
00:41:37I've got to sweat.
00:41:46So it's getting flatter.
00:41:48You see it's flat.
00:41:50It's rotating.
00:41:51It's actually a spiral arms, just like the galaxy I showed you.
00:41:54I've got quite some clumps.
00:41:57Some of them are disappearing.
00:42:00And in this case, I end up with two stars.
00:42:04So this was the first time that people actually could do this.
00:42:09Because when I told you that this cloud was shrinking, the density went up by power 1 and 10 to the power 21.
00:42:20So your computer actually needs to have that range as well to see 1 versus 10 to the power 21.
00:42:30You need a very big computer to do that.
00:42:33And the only real-life situations we have with such compressions are in nuclear explosions.
00:42:39So this is not 10 to the power 21, but we're getting there.
00:42:43Okay.
00:42:44So in a nutshell, my 21 lectures at the third year are essentially in this cartoon.
00:42:54And let me just talk you through it.
00:42:57So we started with a molecular cloud, and its size could be as big, in this case, as a parsec, a few light years.
00:43:07At some point, it could be because simply that's life.
00:43:13Nothing is forever, especially not when you've got the delicate balance.
00:43:17There could be a perturbation.
00:43:18It could be two clouds colliding.
00:43:20It could be a supernova explosion.
00:43:22It could be even me just giving a slap.
00:43:25The cloud starts to shrink.
00:43:28And we call that also the class zero phase.
00:43:34And I'm not going to say too much about it now, but we'll talk about it later.
00:43:39But because it's really cold, we can only see it at very long wavelengths or very low frequencies.
00:43:46Okay.
00:43:47So this is in the far infrared and millimeter.
00:43:50Then at some point, we've got ourselves this disk.
00:43:54And I forgot to tell you when we looked at the movie just now that something went out in both sides as well.
00:44:01So I've got myself a disk and a jet or a bipolar outflow.
00:44:06And from the moment it starts to collapse to this configuration, 10,000 to 100,000 years, we already have something like this.
00:44:18Well, at some point, I don't have a cloud left.
00:44:21So I've got myself a disk and a bipolar flow.
00:44:26Okay.
00:44:27And we can see it already.
00:44:29It's getting warmer.
00:44:30I can see it now at infrared wavelengths.
00:44:33We could talk about it much later.
00:44:35And before you know it, planets can form inside the disk.
00:44:40And either all the material falls into the disk, sorry, onto the planets or it falls into the star.
00:44:47And we end up with a nice solar system.
00:44:52Okay.
00:44:53With planets.
00:44:54And in a way, going from this cloud all the way to a star with planets and everything could happen within a couple of million years.
00:45:04And that is really the blink of an eye for a star, right?
00:45:09I think if we, it takes a pregnancy is nine months, typically.
00:45:14And that's roughly 1% of a human lifetime, roughly.
00:45:20But if I form a star in a million years, and I know that the star like the sun will last for about 10 billion years.
00:45:30That's many times more.
00:45:32So a pregnancy is much quicker when we're talking about stars.
00:45:37Okay.
00:45:38So this is 21 hours at the university in two minutes.
00:45:44Okay.
00:45:45Now I wanted to just show you, talk a little bit about planets with you to finish off the story of star and planet formation.
00:45:54And I think I'd like to start, I hope it's the next one.
00:45:58This is a cartoon where someone actually liked the color orange.
00:46:03And now I'm going to look at real data.
00:46:06And it's almost the same thing.
00:46:08So here I'm looking at an image that was taken only 10 years ago of an object from which we knew.
00:46:18No, it's a young star.
00:46:20And it's got indeed a disc around it.
00:46:24And it's got these carbs.
00:46:27Okay.
00:46:28So the jury is still out whether there's a planet in the gap, because it's really difficult to observe.
00:46:37But it makes sense, doesn't it?
00:46:38If you've got yourself a planet, that it basically just like a snow plow, that it takes all the snow with it.
00:46:44Or in this case, all the material in the disc.
00:46:47And ever since, we have been able to find a lot of young stars with these discs around them.
00:46:59So what we now understand is that really we're looking at, yeah, planets and stars being formed as we speak.
00:47:10These are data.
00:47:11I will show you a little bit more of this later on.
00:47:16This is taken with a telescope that's called the Atacama Large Millimeter Array, ALMA, which is a radio telescope that operates at microwave wavelengths.
00:47:31And it's in Chile at a height of five kilometers.
00:47:35Okay.
00:47:37I'll tell you more about it later.
00:47:40So how do we now think that these planets form?
00:47:45And I think I told you already or I implied that these discs are made out of basically the same dust, molecules and gas as the original cloud.
00:47:58It's basically now redistributed in the pizza.
00:48:01Okay.
00:48:02Now, what happens with that?
00:48:05I want you to mentally think that you're on a beach.
00:48:10You were five years old and you were playing with the sand.
00:48:13And you can't hold that sand.
00:48:14It's always going through your fingers, right?
00:48:16Because it's so dry, you can't hold it.
00:48:19But if you make it wet, they stick together, all these sand grains.
00:48:24Right?
00:48:25So you get mud.
00:48:26And that's the idea here as well.
00:48:29I've got myself a star with sandy grains around it.
00:48:35And if they meet each other and it's wet and we now know it's wet, they stick.
00:48:41So I start with one dust grain, meets another one, meets another one, meets another one.
00:48:45Before you know it, you've got stuff like pebbles that grow even further and further.
00:48:51And when they reach a critical mass, they are so massive, they can actually attract other grains and grow and grow and grow.
00:49:00Okay.
00:49:01So that's the basically the most popular theory up until a few years ago on how we actually get planets.
00:49:12So I start off with these very small dust grains.
00:49:16They meet each other, they grow.
00:49:18And before you know it, and this is also a process that can happen in less than a million years, which is low.
00:49:25Right?
00:49:26But nothing for a star.
00:49:28And so that's how we actually can form planets in the computer.
00:49:33And there's one little extra ingredient.
00:49:37How am I doing for time, Mr. Chair?
00:49:41Okay, that's my excuse.
00:49:47And no one is sleeping yet, so that's good.
00:49:51One extra thing.
00:49:53I think you will agree with me that the further away you are from the star, the colder it is.
00:50:00Right?
00:50:01And the water that I was just talking about, it helps you making this stuff stick.
00:50:08But I've also got CO gas carbon monoxide that will condense into ice when it's further out because the temperatures are so low.
00:50:16So, whereas close into the star, I've got small dust grains.
00:50:23Further out, all these dust grains, they've got this layer of condensed water, ice.
00:50:31So, these particles are much bigger.
00:50:36And because they're bigger, they stick together even better and grow quicker as well.
00:50:43So, automatically, when you think about this, I would expect planets with densities comparable to rock close in because this is arguably nothing more, nothing less than a sand grain.
00:51:00And sand is just a ground rock, okay?
00:51:04But now, I'm adding a lot of water to it, which is a lower density.
00:51:10And these planets become much bigger, much quicker, and then can attract more gas atoms, molecules as well.
00:51:19So, when I go back to my previous questions, the challenge that we had is, can we form small rocky planets close to the star?
00:51:36Well, the model, the theory I just told you about does do that, right?
00:51:41So, I first need to start with the pizza.
00:51:44And then the dust grains, I get these small rocky planets close by.
00:51:48But because of the ice and everything, I expect a bigger planet further away, which we find.
00:51:57And because of this centrifugal force, I expected my cloud to expand like a pizza.
00:52:05And I can work out, don't worry, but we can work out that the force of gravity, when that's equal to the centrifugal force,
00:52:14you can work out the size scale that you would expect.
00:52:18And if you stick in the numbers, you indeed expect that to be flat for up until a few hundred astronomical units.
00:52:27Yeah, and the rest material, that's round.
00:52:31So, that was something that made us very happy until 1995, because we only had one solar system to work with.
00:52:44Right?
00:52:46But that's also a little bit unfortunate if you only have one thing to look at and to explain.
00:52:53But fortunately, since 1995, people have been discovering planets like there's no tomorrow.
00:53:01The counter as of last week is about 6000 exoplanets.
00:53:08We know of 6000 planets outside of our solar system.
00:53:12And that's nice because then we can actually put our models to the test and understand a little bit more about star and planet formation.
00:53:21We might even hope to find some life on these planets.
00:53:24Let's talk about it in a few weeks time.
00:53:26But I wanted to highlight a few of these things.
00:53:30One of the most famous exoplanetary systems is Trappist number one.
00:53:37Which, by the way, is a Belgian discovery.
00:53:40You should be very proud of.
00:53:42Just spoke to the guy who did it the other day.
00:53:47Yeah, they're now working on speculose.
00:53:50I said, yeah, you have to do something to make Belgium known to the rest of the world.
00:53:55I said, well, what's the next one?
00:53:57Mayonnaise?
00:53:58I don't know.
00:53:59But the Trappist one system has no less than one, two, three, four, five, six, seven planets.
00:54:06And they're all equally large as the Earth.
00:54:10And the sun there at the star is much smaller, much cooler.
00:54:17So that's why this is a little bit of a zoom in.
00:54:20Because it's cooler, the place where you have liquid water, which we think we need for life, at least on Earth,
00:54:29is the Goldilocks zone where you might hope the life is, is around here.
00:54:36And that means then you've got three to four planets that are in that sort of liquid water.
00:54:43And our own system, while Mercury is too hot, Venus is just a little bit too far away and it's hot by its own right.
00:54:50But Earth and Mars are okay.
00:54:52Success.
00:54:53So we find systems that we can more or less explain with what I just told you.
00:54:59But the first exoplanets that were discovered, and look at the graphics.
00:55:05I couldn't find a pretty picture because this was how pretty they could make them in 95, right?
00:55:11So I kept it.
00:55:12But the first planets that were discovered were heavy, massive planets, very, very, very close to their host stars.
00:55:20And the reason is that the more massive a planet, the easier it is actually to detect.
00:55:26Okay?
00:55:27We'll tell you more about it later.
00:55:28But just to put it into perspective, this is a planet that's 10 times more massive than Jupiter.
00:55:35And that was a big one compared to Earth already.
00:55:38But it's as close to its host star as Mercury.
00:55:40This one is even closer.
00:55:42But yeah, that is not what I just told you, right?
00:55:49So the theory that I had these small rocky planets close to the star does not, I repeat, does not expect these biggest close.
00:55:59So the first planets that we discovered essentially implied that everything we thought about star and planet formation is wrong.
00:56:11Then we've got here another system where we find a star with three planets around it.
00:56:18This is a time-lapse movie of 10 years.
00:56:21And you can see that the inner planet is moving a little bit faster than the other one.
00:56:26And the nice thing is this is not a very pretty picture.
00:56:30But if we use the best telescopes, we always take them to the limit.
00:56:34So the pictures are not always pretty nice.
00:56:36But so essentially, this is what you see in here.
00:56:40And there's all that crud around the star, which is probably the remnant of the pizza.
00:56:46But, and the next picture probably makes it even clearer.
00:56:51This is another object.
00:56:52And we find a planet here that's moving.
00:56:56And that's even in this case at 200 astronomical units away.
00:57:03Remember that our furthest planets were about 20, 30 AU.
00:57:09This is five to eight times further.
00:57:12We do not, do not expect such big planets so far away from the star.
00:57:20So this is not a problem again.
00:57:24I had this fantastic theory for you that works for our own single solar system.
00:57:31And yeah, now that I've got quite a few counterexamples.
00:57:35And of these thousands of planets that we know, there's not everything we know about them.
00:57:42So I've got not thousands of planets here.
00:57:45But if I plot, if I make a graph of the orbital period of these planets.
00:57:50So that means basically, these ones are very close.
00:57:54And these ones are very far away.
00:57:56And if I look at the mass, these ones are very low mass.
00:58:01And these are very high mass.
00:58:03And for reference, Earth is at 365 days.
00:58:08And Jupiter is five Jupiter masses.
00:58:14So we haven't found these planets yet because it's too difficult.
00:58:21But the ones I was just talking about, these are these gas planets very close to the star.
00:58:26And these are the ones very far.
00:58:28So what do we do?
00:58:30And this is quite an interesting scientific question.
00:58:33If you find something that your current theory doesn't work, what do you do?
00:58:38Do you throw it away and come up with something else?
00:58:43Or do you tinker a little bit with the theory that you have?
00:58:47Okay.
00:58:48And I think with tinkering, it's nothing wrong until you go over the top.
00:58:53But the new ideas that people now have and considering is, they say, well, hang on.
00:59:00Rene, you told me that these dust grains were sticking together, right?
00:59:04But what if these clumps in the pizza collapse just like the big clouds I was talking about in the beginning as well?
00:59:14So instead of just waiting for grains to stick to each other, perhaps gravity will do the job for us.
00:59:22And that's essentially what we call gravitational instability.
00:59:26Perhaps we can form planets just with gravity.
00:59:31And here's not a movie, but here people started off with a rotating disc, press return, let gravity do its thing.
00:59:39And before you know it, you get all these conversations which can form planets.
00:59:44Okay.
00:59:45It's viable, but we still haven't found the small planets here.
00:59:49But that's the state of the art at the moment, right?
00:59:52We go to a new thing.
00:59:54What can we tinker about the existing theory?
00:59:57And people, when people were thinking about it, they thought, well, hang on.
01:00:03Suppose now that these big planets, suppose that they move in.
01:00:08And you can work that out in your computer with something called tidal forces.
01:00:14Perhaps there's one force that's a little bit pulling the planets a little bit more in the direction of the sun than outwards.
01:00:20Okay.
01:00:21And if they do that, perhaps that's how I can get them at least close to the star.
01:00:27And this is not a very pretty simulation.
01:00:32It's a real scientific one.
01:00:34But essentially, everything looks the same size, but resuming in.
01:00:40So this was the planet and it's moving closer and closer to the star.
01:00:44And it actually gives us a gap.
01:00:46And this disc is orange as well.
01:00:48So that's exactly what I wanted from the cartoon early.
01:00:50So the problem that we now have, we've got this embarrassment of riches.
01:00:56We've got thousands of planets, but many of them are not consistent with our theories we had until 95.
01:01:03So on the one hand, we're now thinking about new theories.
01:01:08And on the other hand, we're thinking about, well, perhaps you can tinker a little bit with what we knew already.
01:01:15And in the end, it will be both of them, of course.
01:01:18But that's a different story.
01:01:20But yeah, so that's the state of the art.
01:01:23And we've got the accretion model of planets.
01:01:27And we've got what they call the gas collapse model to form planets.
01:01:31Oh, yeah.
01:01:32Okay.
01:01:33Make the picture and then I move to the next slide.
01:01:34Yeah.
01:01:36And the jury is still out.
01:01:38Okay.
01:01:39So that was the first lecture then out of the series.
01:01:42I hope you got a little bit of a nice overview of what we think of star and planet formation.
01:01:48And I will go into a little bit more detail in the coming weeks.
01:01:52So thank you.
01:01:59Before question, just to remind you that if you are following micro certification, go to Marimo to register for tonight.
01:02:05Now, if you have questions, please.
01:02:12Patrick, can you put the lights on?
01:02:14What will dictate the orientation of the gravitational disk from the cloud to a disk?
01:02:26What will impact the orientation?
01:02:29So the question is, so when is it like this?
01:02:33When is it like this if I've got a collapsing cloud?
01:02:36I think it's fair to say, oh my goodness, I should take a juggling ball with me the next time.
01:02:42But if something is rotating like this, then nothing is rotating on the poles.
01:02:48So it's in the equator where it's rotating the fastest that I would get my pizza.
01:02:54So it's always perpendicular to the rotation axis.
01:02:59That's at least a part of the answer.
01:03:02Do you have more for that question?
01:03:06And so what will impact the orientation of your rotation?
01:03:11Yes, okay.
01:03:12So we think that many of these clouds are more or less rotating in the same plane as our galaxy.
01:03:27So this is incredibly crude and probably wrong, but we would expect until we've got some complications that I might talk about later, that all the solar systems would be in the same plane as the galaxy.
01:03:43Life is a little bit more complicated than that, but that would be the first one.
01:03:47Okay, so we also think that the magnetic field of the galaxy plays a role there.
01:03:54And I was doubting whether I would show it, but I will show the magnetic field of the galaxy later, and I'll get back to that.
01:04:09So white shirt then, and then white shirt.
01:04:14Yeah, yeah, it's closer.
01:04:16I was wondering, how did we find the specific amount of gravity needed to make the molecular cloud to keep it together?
01:04:27You mean by, you mean the observational thing that I told you there's about 10 stars there?
01:04:34Or was it the theoretical thing that I said, this is the critical mass rate to collapse?
01:04:39These are two different things, so.
01:04:41The observational one.
01:04:42The observational.
01:04:45Well, let's just think about this.
01:04:47How many hands do I need to block the entire screen, right?
01:04:50So, I don't know, many.
01:04:52And I can do exactly the same exercise with blocking all the light from the background stars that I showed you in the picture.
01:05:00And then I know the size of such a cloud, then I assume it's round, so it's this size in that direction, in this direction.
01:05:07And then I basically work out the density and multiply it by the volume.
01:05:12So, it's really crude, but it works.
01:05:19So, I have two questions.
01:05:23Firstly, why does everything rotate?
01:05:27And secondly, is our Oort cloud, is that a remnant of our pizza?
01:05:35Okay, first one.
01:05:38Why does everything rotate?
01:05:42I don't know.
01:05:44But I think it's fair to say that nothing, nothing does not move.
01:05:50And I think if you give something a kick, then it probably would start some sort of rotating motion.
01:06:00And I'm making this up as I go along.
01:06:03I hope I'm not too wrong.
01:06:04But that rotation becomes stronger and stronger, the smaller and smaller you get, and becomes more dominant.
01:06:10So, even if I start with something that is not even rotation, but just a movement in one direction, it can end up becoming like a...
01:06:18It's almost like the water in the sink, right?
01:06:21So, it's almost inevitable, but I will find it very difficult to explain it to you from first principles and believe it myself.
01:06:29And the second question was...
01:06:34Yes.
01:06:37Well, the pizza is flat.
01:06:39So, it's basically the remnant of the cloud itself.
01:06:42But I also...
01:06:45There's something that I really did not talk about, and probably will not, is that once you've cut yourself a solar system, then you've got an extra complication because the Jupiter is pulling an asteroid or a comet.
01:07:00And people actually think that the moon is there because another planet smashed into Earth and broke it into two.
01:07:08But that other planet smashed into Earth because of Jupiter pulling it.
01:07:12So, even big planets can move about because of Jupiter doing its thing.
01:07:17So, my guess is that all the particles in the Oort cloud, they were probably formed both in the molecular cloud itself, but also just dispersed pebbles that were formed during the star formation process.
01:07:32But these are high-level questions, actually, because it's very difficult to investigate as well.
01:07:39So, let's go.
01:07:40Let's go.
01:07:41Let's go.
01:07:42Let's go.
01:07:43Let's go.
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