- il y a 6 heures
The final agony of stars is often observed across many galaxies as supernovae, but they can also die quietly in despair. In their wake, they leave behind mesmerizing and mysterious remnants, some of which even lack a physical surface. During the lectures, we will peek behind the veil of secrecy of these compact objects, where gravitational, nuclear and electroweak forces are pushed to their extremes in an exciting competition for dominance.
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ÉducationTranscription
00:00:00Okay, thank you, Thibaut, for the presentation.
00:00:04Hello, everyone, again.
00:00:06I'm Nikolai.
00:00:07It's very nice to meet you.
00:00:09Again, thank you for coming to my lecture.
00:00:12Today we'll be talking more about neutron stars.
00:00:16I'll explain why and so on.
00:00:20And again, I'm encouraging you to ask me questions during my talk.
00:00:25I think it is the main purpose, actually, for me being here,
00:00:29because you could maybe find some nice lecture on YouTube or something else,
00:00:34but you cannot ask questions.
00:00:35Here you can.
00:00:36I am happy to answer to you.
00:00:38So neutron stars.
00:00:41But first, we need to revise or remind what was last time,
00:00:48but the best revision is an exam.
00:00:50So prepare yourself.
00:00:54So the first question is like, where stars born?
00:00:58We went through it last time.
00:01:01Do you remember like?
00:01:03It's like, do you have any idea in which exactly place where they born?
00:01:08In which nebulas?
00:01:10Eagle.
00:01:11Eagle is right.
00:01:13But others maybe?
00:01:15Yeah.
00:01:16Yes.
00:01:17Everywhere here.
00:01:19All four answers are correct.
00:01:22No, no, no answers here.
00:01:25So, and we study last time that first we have like a H2 like molecular cloud of hydrogen.
00:01:32Then if it reaches certain mass, it starts to collapse here.
00:01:37And then forming kind of accretion disk, because in the system it's always kind of same rotation.
00:01:42And then there is accretion disk, some kind of ejection with the jets.
00:01:47And then the star is forming the center.
00:01:50And then this accretion disk, the planets are formed and so on.
00:01:53And here in the center, the star starts to work and generate power with nuclear reactions.
00:02:00And yeah, we see it here.
00:02:03Here we have sun and so on.
00:02:05And then the nuclear reactions, it produce.
00:02:08The maybe you remember, which is the most strong bound elements in this ice in stars?
00:02:17Which sorry?
00:02:22Helium.
00:02:26So it is the most strongly bound element that star can produce, I think.
00:02:32Helium.
00:02:33Or iron.
00:02:35Yeah, iron is correct.
00:02:38So our sun produce only helium, but just because it's actually small.
00:02:43We were talking, but actually the most bound element that can be produced is iron.
00:02:50Here's the binding energy, or in other words, how much energy you can gain by putting all these
00:02:58nucleons together in the bound nuclei.
00:03:01So this is what's called bound binding energy.
00:03:04And the most bound is iron.
00:03:06That's why, I mean, Earth is mostly iron actually in the center.
00:03:11That's why we have it a lot everywhere.
00:03:13But this is the maximum you can produce.
00:03:16If you have the star where you have iron core and you want to have more energy, you want
00:03:22to sustain, you want to prevent from gravitational collapse, you cannot.
00:03:27And actually, this is a very important consequence here.
00:03:32And we will study later why and what implication does it have.
00:03:37Yes, sure.
00:03:46Yeah.
00:03:47So these are extreme processes, which I usually have.
00:03:52I will talk about this maybe in the, well, maybe not in the end of our lecture today,
00:03:58but maybe on the next lecture.
00:04:01In the extreme processes, for example, on the neutron star, where you have a lot of energy
00:04:06injection in the system, and then you can synthesize heavier elements.
00:04:11Or for example, if you have iron and then in the same time you have hydrogen.
00:04:17So we need to compare energy of iron with hydrogen and energy of the element that you can create
00:04:22connecting hydrogen to iron.
00:04:24And then hydrogen has no bound binding energy.
00:04:28So then from hydrogen and iron, you can create something else.
00:04:31And this, for example, proton captures.
00:04:34It's called P process or RP process, which is rapid proton capture.
00:04:40Very important process in neutron star mergers.
00:04:44But this is spoiler.
00:04:46But it's a great question.
00:04:48Indeed, only like in critical conditions, we can create them in stars.
00:04:52Usually when the stars explode, it's iron mostly.
00:04:56Some elements are also synthesized and so on.
00:04:59But yeah.
00:05:01Then we go for the next question.
00:05:04What happens with a star in this mass range when they die?
00:05:09Do they become brown dwarf, red dwarf, yellow dwarf or white dwarf?
00:05:16Who is for red dwarf?
00:05:19Please raise your head.
00:05:20Okay.
00:05:21One, two, maybe.
00:05:22Who is for white dwarf?
00:05:25Okay.
00:05:26Most.
00:05:27Almost.
00:05:28Okay.
00:05:29White dwarf is correct.
00:05:31So brown dwarf is actually very small star and it's lower in the mass range.
00:05:38And it is not massive enough to start burning hydrogen.
00:05:43Red dwarf is in this mass range, but it's actually a live star.
00:05:47And it's like working.
00:05:48It's not, it's not that star.
00:05:50Well, yellow dwarf is our sun.
00:05:54And the white dwarf is a degenerate star.
00:05:58And we started last time that stars, then they spend most of the life on the main sequence
00:06:03here at this point.
00:06:05Here is luminosity versus surface temperature of the star.
00:06:10So some, for example, spends here 9.5 billion years just in this point.
00:06:15And then in the end of its life, when the hydrogen is depleted in the core, it starts to expand
00:06:22and burn by hydrogen in the envelope.
00:06:24It goes here.
00:06:25Then helium burning.
00:06:27Then again, extending.
00:06:28And then it ejects and loses an envelope moving here on this track and then become white dwarf.
00:06:37And the white dwarf, as we discussed last time, is a very small dead star.
00:06:44And it's actually like Earth, the size of the Earth.
00:06:48But then it contains about one or more solar masses.
00:06:51So it's very dense star.
00:06:53And it maintains its hydrostatic equilibrium because of the pressure of degenerate electrons.
00:07:02Last time we went also through it that, for example, we all studied like in chemistry,
00:07:08when we put electrons on some orbitals in atoms.
00:07:11And here we have like electrons spin up, electrons spin down.
00:07:15And we always need to put electrons on the next orbit.
00:07:18We cannot put all the electrons on one orbit.
00:07:22This is kind of important principle in quantum exonics because electrons are fermions.
00:07:28And you cannot put more than one fermion in the phase space.
00:07:33Sorry.
00:07:34In one cell of the phase space.
00:07:36So if you try to do this, you kind of create degenerate gas.
00:07:39And you try to compress them, you have kind of response of the system.
00:07:44And the associated pressure depends on the density.
00:07:47That's why white dwarf doesn't collapse and maintains energy.
00:07:51Sorry.
00:07:52Pressure with gas of degenerate electrons.
00:07:58And we also obtained Chandrasekhar limit on the mass of the white dwarf, which is around 1.5 solar masses.
00:08:06So if you have white dwarf with more than this mass, it should collapse.
00:08:11It cannot be stable.
00:08:13Less is OK, but more just cannot.
00:08:17And the interesting thing that we obtain just for some Fermi particle, it can be electrons.
00:08:23And with electrons, we can have a size of the star, which is around 5,000 kilometers like Earth.
00:08:29And if you have gas of the neutrons, it will be much smaller around three kilometers on this in this simple estimations.
00:08:37So it's already kind of we are predicting that could exist some objects which are even more dense and still stable.
00:08:45So then we go further.
00:08:48Where is the black hole?
00:08:53Here's already answer.
00:08:56It's there, but it just having fun.
00:09:01And what is your quest?
00:09:03I don't know how popular is Monty Python and Belgium.
00:09:06But then could you find the airspeed velocity of unleavened swallow?
00:09:10But OK, just a joke.
00:09:16So more important question is like what is known supernova?
00:09:20Because in the end I discussed it, but maybe I didn't do my job well.
00:09:25So today I wanted to correct the mistake.
00:09:29So here we have one system which has explosion of matter on the surface of a white dwarf.
00:09:37And you see here kind of the matter is expelled.
00:09:39And the other where we have complete disruption of a white dwarf.
00:09:44And you see it produces a lot of iron.
00:09:51So, I mean, as you can guess, Nova is here because it has luminosity of like a hundred thousand suns.
00:10:01And the champagne supernova in the sky has five billion suns luminosity at some point.
00:10:11And the interesting thing about white dwarf's collapse.
00:10:15It is always, I mean, it has some mass limit, which is 1.4 solar masses.
00:10:21Well, approximately this.
00:10:23So every white dwarf which collapsed in the universe had these months.
00:10:28So it's kind of like all the supernovas are actually 1A of this class are actually very similar.
00:10:37It's always like this star collapses and produces the same luminosity.
00:10:43So it can be used and it's used in cosmology as standard candle.
00:10:48So you have a candle and you have, you know, the luminosity of the candle.
00:10:52And if you put it on larger distance, you see it like dimmer for sure.
00:10:57But then, you know, like from the physics law that luminosity scales as inverse proportional to the distance square.
00:11:05And then, well, we put it even farther away.
00:11:07So if you see the candle and you know it's luminosity like near you, you can already say, even if it is too deep,
00:11:15you can already say that what is the distance to this candle.
00:11:19And the same with the stars.
00:11:21Like this supernova 1A can be used as standard candles.
00:11:28So when we see it, we already know the distance to the object.
00:11:32Then the other thing is like people measured lines coming from the supernova.
00:11:39So, for example, there is a particular photon from some line coming from, I don't know, like decay of nickel to iron, for example.
00:11:51And we know in the laboratory that it should correspond to this frequency or to this energy of the photon.
00:11:58And we know, for example, the spectrum.
00:12:00So we know the sequence of the lines.
00:12:02And then we look at some supernova in the sea, the same sequence, but it's kind of like shifted.
00:12:08And this is what is called usually redshift.
00:12:11And in cosmology, actually, like in cosmological models, it can occur because the universe is expanding.
00:12:21For example, the object is moving far away.
00:12:23We know it's like a Doppler shift and the object is moving.
00:12:26It becomes away from us.
00:12:28It becomes a bit redder.
00:12:30It's because actually the wavelength is kind of like is expanded, is extended.
00:12:35It's the same with the universe.
00:12:37We say if it is expanding, then we see that the wavelength is changing.
00:12:43And then we can look at the different stars and different distances and see how the wavelength changed.
00:12:50And people come up with actually results.
00:12:53The universe is not only expanding, but it's expanded with acceleration.
00:12:57And then people obtain Nobel Prize for this.
00:13:04Then this was explosion of white worth that is composed of carbon mostly.
00:13:10But what happened if white worth is a bit more dense in the center and have like other elements like oxygen, neon or magnesium?
00:13:22Actually, there is a certain limit.
00:13:24And then you start to compress the white worth if you start to put matter in it.
00:13:27Then at some point, these elements start to capture electrons.
00:13:31But electrons are crucial for white worth.
00:13:34As you remember, electrons that are particles who maintain pressure, who hold equilibrium.
00:13:39If you just start to take out electrons from the system, nothing prevents.
00:13:44And this star starts to collapse.
00:13:46And then you can actually form neutron star.
00:13:49And here's kind of like branches of stable stars, which have tamed from hydrostatic equilibrium equations.
00:13:59And here is a branch of white worth.
00:14:01You see it like the size about like 5,000 kilometers or 10,000 kilometers.
00:14:06And there is another actually stable branch, which is called neutron stars.
00:14:10And in principle, also still unobserved.
00:14:13Really, it's kind of hypothesis.
00:14:16But actually white worth can collapse to a neutron star.
00:14:19So, okay.
00:14:20And this was our last lecture that we went about like low mass stars, like sun like stars, which
00:14:32becomes red giant or like red dwarf and so on.
00:14:35And today we'll be talking about more massive stars that produce, can produce neutron stars
00:14:40in the center.
00:14:42So neutron stars.
00:14:46So if we are talking about evolution of massive stars that has more than eight solar masses.
00:14:51So they usually can burn elements that produce this, again, oxygen, neon, magnesium.
00:14:56It's kind of the same as a white worth.
00:14:58And then electron captures can remove support and provoke collapse on the star.
00:15:03But the difference with the collapse of white worth that here we also have an envelope of the star.
00:15:08Before we have, we had just white white worth with 1.4 solar masses.
00:15:13Now we have 10 solar masses star with a huge envelope.
00:15:17So before we could have like some of collapse, but it would be small or dim or subluminous supernova.
00:15:24Here we can have much more energy as you will see.
00:15:28Then if we have bigger stars, then we can produce iron in the core because we have kind of larger temperature in the center.
00:15:37And we can synthesize having heavy elements.
00:15:40But as I told you before, we cannot have more energy.
00:15:43We just have iron there.
00:15:45No energy can be produced.
00:15:47And either electron captures or actually because the temperature is so big that it starts to photo disintegrate iron.
00:15:54So like there is some like gamma photons which kick the iron and then disintegrate it to helium and neutrons and start to remove support from this star.
00:16:05And the core exceeds Chandrasekharan limit and this inevitably leads always to collapse.
00:16:12And then what happens next?
00:16:16So you remove support from the center of the star.
00:16:20It starts to contract at some point and then more and more material kind of falls and falls on the star.
00:16:27Actually, if you look at the star at this moment, you cannot notice this.
00:16:30The star looks to be OK.
00:16:32It's just that in the center, it's already collapsing.
00:16:35It's already dead actually.
00:16:37And then at some point, the core contracts to critical density and stop contracting more.
00:16:45And then the matter falls and it's kind of like you imagine you have a ball.
00:16:49And then you put the matter, it kind of bounces and creating the shock wave which starts to expand outwards here for example.
00:16:58And then it drives all the material away.
00:17:01It ejects all the material out.
00:17:03It's kind of simplistic picture of a supernova.
00:17:06But in reality, this is called this is called prompt collapse mechanism.
00:17:12In reality, in the simulation, it usually fails and cannot produce supernova because the shock starts to disintegrate all the other elements.
00:17:21It loses energy and it stalls.
00:17:23And what can revive the shock is usually is 3D models with some fluid instabilities, neutrino transport, magnetic fields, rotation, everything included.
00:17:34And then people can successfully.
00:17:37It's only actually recently.
00:17:38Like I remember when I was studying course on supernova like, I don't know, six years ago or something like this.
00:17:44There was no actually really good model that can explode.
00:17:48Now it's it's very active field.
00:17:50Now people successfully can explode and explain observations.
00:17:54Because observation they see that supernova exists and they explode.
00:17:57It should work.
00:17:58And we should reproduce this result.
00:18:01This is this is a goal.
00:18:03Yes.
00:18:04Yeah, it's very fast.
00:18:09It's very fast.
00:18:10Yeah, so the collapse happens quite fast, but then actually I don't put here a light curve.
00:18:22But actually, you cannot see it inside the star unless the shock wave reaches this called photosphere.
00:18:31It will start to see like photons from it and then it's kind of a bit later when we see.
00:18:36And then what is like the peak luminosity that you see is actually from radiative decay of the elements.
00:18:42So it's like a bit later.
00:18:44But indeed, this is the point that ideally you want to see supernova from the very beginning.
00:18:52So ideally, you want to already point the telescope in this point in the sky and already know about supernova.
00:18:59But unfortunately, it's not always the case.
00:19:03You cannot always do it.
00:19:04You don't know.
00:19:05And there actually exists alert system.
00:19:07So there are many small telescopes.
00:19:09So big telescope costs a lot of money, have small field of view.
00:19:14And it's usually like following sources and so on has very strict program.
00:19:18Small telescopes can have a bigger field of view, less expensive.
00:19:23You can build a lot of them.
00:19:24And there is a lot of programs like small telescope looking in the sky is actually just scanning the sky.
00:19:30It's looking for supernova.
00:19:32And then something happens, small telescopes just writing alerts.
00:19:37Usually there is some guy who is like doing observation is like, oh, everyone, look there.
00:19:41There is a supernova.
00:19:43And then the other astronomers point their telescope immediately if it is allowed.
00:19:47Immediately to this point because they want to see the peak luminosity and what happens there and so on.
00:19:55So it's it's a really big deal in astronomy and it's like collaborative research and so on.
00:20:01So excellent question.
00:20:03Yes.
00:20:07So, yeah, we will we will come to this point.
00:20:11Great question.
00:20:13So, as I said, during the collapse, like there is a lot of mass going on here in explosion and a lot of neutrinos are produced.
00:20:21So they're firstly produced in the reaction of electron captures on some elements.
00:20:26So electron plus proton gives you a neutron, which everyone knows, but it also gives a neutrino particle which can easily escape.
00:20:34Well, actually, for the first like one or two seconds neutrino can be trapped.
00:20:39But then it's usually escapes and from the outer layers, it's usually escapes.
00:20:44And then the temperature is so high that it produces electron positron pairs that also can annihilate and then create more neutrinos.
00:20:52And actually, the interesting thing, the neutrino carry away ninety nine percent of the energy of the explosion.
00:20:59And we see the rest.
00:21:00We see only one percent.
00:21:02Ninety nine is in neutrinos.
00:21:05And the people wanted to detect them and they actually need it.
00:21:11But by a bit of coincidence, this is what is shown.
00:21:16is Super Kamiakande detector.
00:21:20It's a huge detector of neutrino.
00:21:22It's like a giant tank which is filled with water.
00:21:26And there are a lot of photomultipliers here.
00:21:29So if neutrino comes to the detector, it actually recoils with electron and muon.
00:21:35Then muon moves faster than local speed of light.
00:21:39And then it starts to meet.
00:21:40This is called Cherenkov effect.
00:21:41But this is another lecture.
00:21:43I don't have time to explain in the more details.
00:21:48Just believe me that it emits.
00:21:50And then these photomultipliers can detect it.
00:21:53But actually, this experiment is a failed experiment.
00:21:58Because it was built to detect proton decay, which was never observed.
00:22:03So people spend a huge amount of money, build a detector, which never detect what they wanted.
00:22:10They wanted to see the proton decay.
00:22:12But they know the proton is super stable because we have a lot of hydrogen.
00:22:16Imagine if proton would decay.
00:22:18It would be a huge thing.
00:22:21But this detector kind of a bit by coincidence is a bit not.
00:22:27And then Nobel prices were also for this were given.
00:22:33It detected neutrinos from the supernova.
00:22:36This is super famous.
00:22:37Supernova 1987A in large Magellani cloud.
00:22:41It's kind of the closest supernova really observed with a lot of telescopes and sound.
00:22:47There are like thousands of maybe more than thousands of papers written on it.
00:22:52And this telescope detected like maybe actually 15 events or something like this.
00:22:59Of neutrinos.
00:23:00Only 15 events.
00:23:01But they proved that it came from this source.
00:23:04And it was like a huge thing.
00:23:06And the other telescopes who saw this it's IMB in the US.
00:23:11And also Baksan Neutrinos Observatory in USSR.
00:23:14And actually this is me.
00:23:18Six years ago I went to the student to the school.
00:23:21And here a Sinterlander array which detected.
00:23:24They had like maybe five neutrinos and so on.
00:23:27But still everything coincided with like second to second.
00:23:31So it's like a good statistical threshold on this.
00:23:37So yes indeed they detected it.
00:23:41And here is the stack of the images from Hubble Space Telescopes.
00:23:47So actually these rings that you see.
00:23:49These are not from the supernova.
00:23:51This as we as we.
00:23:52Yeah sorry.
00:24:16Yeah great question.
00:24:17So first of all I mean supernovas they explode not on the same time.
00:24:21So when supernova explodes it has a peak in neutrino emissivity.
00:24:25And then there is usually kind of like.
00:24:27In our galaxy it's predicted that one in 100 years.
00:24:30But we already like spent maybe 150 years.
00:24:33And we still didn't see one.
00:24:35But the predicted rate is kind of like this.
00:24:37So if you if there is one supernova you for sure will see it.
00:24:40The other thing as you mentioned a lot of supernovas emit a lot of neutrinos and neutrinos are floating everywhere.
00:24:50And there are actually projects trying to detect this kind of background of supernova neutrinos.
00:24:56So I'm trying to see kind of like on average if all the supernovas produce neutrinos and so on.
00:25:02But yeah it is kind of another another field of research.
00:25:08Here's like you clearly can see.
00:25:11If you say you have kind of like level of neutrino emissivity boom.
00:25:16And then you clearly can I did.
00:25:20Identificate that this is the thing.
00:25:23Yes.
00:25:31So this supernova so of core collapse supernova they don't have the same luminosity.
00:25:38Actually they are very different.
00:25:39It's only supernova 1a when you have explosion of white dwarf which is disrupted.
00:25:45Then you have the same luminosity because basically you kind of have the same white dwarf like of the same mass.
00:25:51Which exploded with the same mechanism basically.
00:25:58Yeah.
00:25:59Yeah.
00:26:00For supernova 1a.
00:26:01This is core collapse supernova.
00:26:02They can be like supernova supernova of type 2.
00:26:05Or there is actually one BCD.
00:26:07It's a huge mass of category.
00:26:09I don't want to spend time on this.
00:26:11But these cannot be used because it's very different actually from supernova to supernova.
00:26:19There are like some sub luminous other ultra luminous.
00:26:22So it's like a huge zoo of different supernovas depending on magnetic field and progenitor and so on.
00:26:29So it's like a lot of so this you cannot use.
00:26:34But we usually see it on the on the on the in some galaxy.
00:26:38And sometimes we can identify the galaxy where it came from.
00:26:41So then we kind of try to estimate the distance and so on.
00:26:45I mean and then the energetic is kind of close but it's not like standard.
00:26:49Yes I wanted to finish the point that these rings actually came from the progenitor star when it lost its envelope where we discussed last time.
00:27:00And then in the end of the star it's kind of like there is some pulsation.
00:27:04It is inject the envelope and then the supernova exploded and then you can see.
00:27:11So here at some point it will explode from the beginning.
00:27:16Yeah so now it's exploded you can see it's bright and then the material here reaches the ring and kind of heat is up.
00:27:23It's kind of like shock here and so on.
00:27:25And this is what is shown here on this image.
00:27:30OK, so then there are some like again historical example supernova.
00:27:35Maybe the most famous is a supernova in Crab Nebula.
00:27:40You can see here with the Hubble Space Telescope.
00:27:44The image is like you can see it in the kind of like a material telescope.
00:27:51Also this is in the X-ray how it looks like here what is created and kind of in the center.
00:27:58Here we have different structures.
00:28:00We will discuss them a little bit.
00:28:02And here's actually my image made on a mirror cutter telescope.
00:28:07How do you like it Timo?
00:28:12Not bad.
00:28:13But I think it's actually nice because here you can see kind of like a hands.
00:28:18And it's looking this like a crab.
00:28:20Well here a white crab.
00:28:22I don't know.
00:28:24Of course like the quality of that image is much better and so on.
00:28:29But it's just to show you just for fun.
00:28:33So if the mass of the progenitor star is higher.
00:28:37And then the matter starts to collapse.
00:28:39And when the object in the center cannot prevent collapse.
00:28:43It actually just goes to the black hole.
00:28:46And we will discuss it later.
00:28:48Of course black holes are fascinating.
00:28:51But what is more interesting?
00:28:54Black hole or neutron star?
00:28:56You can see the comparison in physics.
00:29:03Then we discuss what happens in the center.
00:29:06There was a question like why it stops and what happens with the core.
00:29:10So for example we have your iron atoms.
00:29:14And then you start to squeeze them.
00:29:16You can start to squeeze the matter.
00:29:18They come closer here.
00:29:20Even more closer.
00:29:21Here you have already nucleons that compose nuclei.
00:29:25And even closer the nucleus starts to be free.
00:29:29And then everything actually becomes kind of homogeneous at some point.
00:29:33And all the processes kind of mediated here.
00:29:36They are because of the nuclear force that we discussed.
00:29:40And the nuclear force we know that it forms nuclei from nucleons.
00:29:45And we know it's attractive because they are bound.
00:29:48But it doesn't lead to collapse of the nucleus.
00:29:52And this is because unlike gravitation.
00:29:55So if you have gravitation it can lead to collapse.
00:29:58So it's quite strong.
00:30:01Here you have attractive potential of the nuclear force.
00:30:05And in the center you actually have a repulsive core.
00:30:08So if you have two nucleons they like to be with each other.
00:30:12But they do not collapse kind of like in one point in some singularity and so on.
00:30:16At some point there is a repulsive core who stops it.
00:30:19And they usually are located kind of like in this potential kind of the most energetically favorable point.
00:30:26It's kind of like there and they stay there.
00:30:28And actually this is what stops columns.
00:30:30If you start to squeeze it.
00:30:32Yes there is method degeneracy.
00:30:34At the first people think.
00:30:36People thought that neutrons stop it because of the degeneracy.
00:30:39But it is not enough.
00:30:41And actually nuclear force here what stops the columns.
00:30:45So a bit of background on how neutron stars were predicted and then discovered.
00:30:52So James Chadwick discovers neutron in 1932.
00:30:56And then he has like three years later only he has Nobel Prize.
00:31:00There are a lot of claims in the literature.
00:31:03Even in the standard book that actually left Landau.
00:31:06Predicted neutron star which is not true.
00:31:09He predicted that in the core of the massive star.
00:31:13There could be some kind of objects with a density which is close to the density of nuclear matter.
00:31:21But when he wrote it he didn't know about discovery of neutrons.
00:31:24So he could not say that this is neutron star.
00:31:27Well he had his Nobel Prize for other reasons.
00:31:31And it's actually Bade and Zwicker.
00:31:33Zwick is father of dark matter also.
00:31:37That predicted that neutron stars are born in supernova.
00:31:40Also in the details in the paper they discuss the neutrons can form on the surface.
00:31:45And then leak in the center because of the gravity which is not true.
00:31:49But still it was them who predicted neutron stars.
00:31:55Then in the 1939, Tolman, Oppenheimer and Volkov.
00:32:00You could probably know the movie.
00:32:03Actually Tolman I think also is in the movie.
00:32:06So you can find him.
00:32:08They analyze the stability of neutron star.
00:32:12Oh sorry.
00:32:13Stability of neutron course inside the stars using general relativity.
00:32:17So again they're kind of like resolving equations in general relativity in spherical symmetry.
00:32:25And these are now called Tolman-Eppenheimer-Volkov equations.
00:32:29And they obtain some limit.
00:32:31So you could see it like on top in the point C.
00:32:34But at that time they used just degenerate guys of neutrons.
00:32:38And they obtain the limit of 0.7 solar masses.
00:32:42So we know that white dwarfs have limit 1.4.
00:32:47So you will never create a neutron star.
00:32:50If white dwarf collapse it already has mass more than the highest possible mass of the neutron star.
00:32:57So at that time if I obtain the limit and they say well possibly we will never see a neutron star.
00:33:03We never detect it's only a hypothetical object.
00:33:05Or there are repulsive forces that can lead to actually to higher limit.
00:33:14And indeed there's kind of like models of the so-called equation of state of the neutron star.
00:33:21Is dependence of pressure on density.
00:33:24But actually describes you the kind of the properties of the nuclear interaction.
00:33:29How it reacts when you try to compress it.
00:33:32And here are the models of the mass and radius over neutron stars.
00:33:37Here they kind of have some plateau.
00:33:39Then they go up.
00:33:40And then they reach the stability point here.
00:33:43If you go here it's already unstable branch.
00:33:45And there is kind of a limit of about 2 to 2.5.
00:33:51Actually special relativity can put kind of a stricter limit.
00:33:59That you the speed of sound inside neutron star should be always lower than speed of light.
00:34:06And this was shown by Roades and Ruffini.
00:34:09And then you have kind of limit of 3 solar masses.
00:34:12But it's kind of like which is now kind of standard values is 2 to 2.5.
00:34:18Something like this.
00:34:19Then the neutron star.
00:34:22Like what is it like again.
00:34:24It's a giant wall in the space.
00:34:27Actually the size is close to the size of Brussels.
00:34:29It's a bit bigger.
00:34:31And is it possible to detect neutron star.
00:34:34So here is like it has like 12 kilometers.
00:34:38Typical size of the city.
00:34:40Or like in the scientific especially in American like scientific movies.
00:34:44It's everything is measured in football fields.
00:34:47And then this is a kind of typical mass of the neutron star.
00:34:51In comparison to Earth.
00:34:53And the density in the center can be 5 times normal.
00:34:56Nuclear saturation density.
00:34:58And here actually models constructed in Brussels.
00:35:01Of the neutron star equation of state.
00:35:03And here observations.
00:35:04I will talk about them later.
00:35:06But actually in some kind of like vulgarization talks.
00:35:12You could hear that neutron star matter.
00:35:15If you take the sugar cube of neutron star matter.
00:35:17Or a spoon of neutron star matter.
00:35:19It would weight 1 trillion kilograms.
00:35:22Just kind of like for you to imagine.
00:35:24But actually you cannot create sugar cube of the neutron star matter.
00:35:28And bring it to Earth for sure.
00:35:30Because actually neutron star has also minimal mass.
00:35:33Is around 0.1 solar masses.
00:35:36If you put less mass.
00:35:38Then the neutron star just explodes.
00:35:40So there is kind of a plateau.
00:35:42And then there is unstable point here.
00:35:44So it's also interesting.
00:35:47But more realistic minimum comes from the observations.
00:35:51And here the masses of neutron star.
00:35:53And you can see that all of them are around from 1 solar mass to 2.1.
00:36:00Maybe solar masses here.
00:36:01A lot of masses.
00:36:02And they all obtain in the binary system.
00:36:05Because actually when you see the star.
00:36:07I mean as far you have luminosity of the star.
00:36:10But you don't know the mass.
00:36:11I mean you have no idea about the mass usually.
00:36:13And it's only if you have like some orbital periods.
00:36:17And like another star.
00:36:19Only from the movement.
00:36:21Then you can obtain the mass of the star.
00:36:23So only in binary system.
00:36:24You can have like really good measurement.
00:36:29And the more realistic minimum is 1 solar mass.
00:36:33Also in supernova explosions.
00:36:35People cannot produce less.
00:36:38So you need to for good collapse.
00:36:41For really successful collapse.
00:36:43You need at least 1 solar mass in the center.
00:36:47So but again it's like small wall.
00:36:51Like in the space.
00:36:52Like of 12 kilometers radius.
00:36:55Is it possible to detect it?
00:36:57It should be not luminous enough to be seen.
00:37:02Especially in like in the 1930s, 1940s.
00:37:10People actually were quite skeptical.
00:37:12About looking for a neutron star.
00:37:14And they kind of okay.
00:37:15Just like kind of academic task.
00:37:18To try to derive what is the maximum limit.
00:37:20What is a neutron star and so on.
00:37:22You can play around.
00:37:23But it's easier.
00:37:25Nothing to do with it.
00:37:26And then they were found.
00:37:29In the 60s.
00:37:30But the 10 time people didn't understood.
00:37:33That found them.
00:37:34Actually team under.
00:37:36Very famous professor Giacconi.
00:37:39Launched x-ray detector in space.
00:37:42On this kind of like a small rockets.
00:37:44This kind of American rockets.
00:37:45That they used to launch.
00:37:47Satellites on the orbits.
00:37:50Kind of like small.
00:37:51For science.
00:37:52Or for some other purposes.
00:37:54And they detected the first x-ray source.
00:37:57Coming outside solar system.
00:37:59And the interesting thing.
00:38:00That the very first source.
00:38:02They detected.
00:38:03Was neutron star.
00:38:04But they didn't know about this.
00:38:06So they detected.
00:38:07Scorpius x-1.
00:38:08Scorpius x-1.
00:38:09Sorry.
00:38:10Because it is in this.
00:38:13So x-1 means it is the first source.
00:38:19And it's turned out to be neutron star.
00:38:21And in the 1966.
00:38:25Iosif Shklovsky actually proposed.
00:38:27That radiation could come.
00:38:29From matter falling on a neutron star.
00:38:31So as we discussed.
00:38:32If you have.
00:38:33Binary system.
00:38:34And some star fields.
00:38:36It's row slope.
00:38:37So in other words.
00:38:39You have some points here.
00:38:40It's called like.
00:38:41Lagrange point.
00:38:42Where the particle.
00:38:44Is equally attracted to.
00:38:46Big star.
00:38:47And to small neutron star.
00:38:48And it starts to actually.
00:38:50To to.
00:38:51It is a stable point.
00:38:52So then.
00:38:53You move for example.
00:38:54Here.
00:38:55And then you.
00:38:56Because you have some angular momentum.
00:38:57You create.
00:38:58Accretion disk.
00:38:59And in the end.
00:39:00You lose it.
00:39:01You radiate.
00:39:02And then you fall.
00:39:03On the neutron star.
00:39:05Actually.
00:39:06It is the.
00:39:07Most.
00:39:08Profitable process.
00:39:09To create energy.
00:39:10So if you have something.
00:39:12With you.
00:39:13And you let it fall.
00:39:15On the earth.
00:39:16It will give.
00:39:17All its potential energy.
00:39:18To the heat.
00:39:19Actually.
00:39:20Well.
00:39:21You could not notice.
00:39:22Because it's.
00:39:23Very little heat.
00:39:24But if you.
00:39:26If you drop something.
00:39:27On the neutron star.
00:39:28It can create.
00:39:29Like 10 to 20 percent.
00:39:31Of the rest mass.
00:39:32Of this object.
00:39:34In comparison.
00:39:35With nuclear reactions.
00:39:36When you have.
00:39:37Only 1 percent.
00:39:38So it's.
00:39:39Much more energetic process.
00:39:40And it's emitting.
00:39:41In x-rays usually.
00:39:42But neutron stars.
00:39:45Were discovered.
00:39:46A bit later.
00:39:47And it's.
00:39:48Called.
00:39:49Serendipitous.
00:39:50Discovery.
00:39:51So.
00:39:52By coincidence.
00:39:53Or by happy chance.
00:39:54So.
00:39:55Anthony Hughes.
00:39:56Designed.
00:39:57A new array.
00:39:58Of antennas.
00:39:59In Cambridge.
00:40:00And then.
00:40:01His student.
00:40:02Jocelyn Bell.
00:40:03Was.
00:40:04Analyzing.
00:40:05The data.
00:40:06Array of antenna.
00:40:07In Cambridge.
00:40:08I heard.
00:40:09That they use.
00:40:10Sheeps.
00:40:11To destroy.
00:40:12All the grass.
00:40:13Because they could not.
00:40:14Put.
00:40:15Loaning machine there.
00:40:16So it was like.
00:40:17Very interesting story.
00:40:19And.
00:40:20His student.
00:40:21Jocelyn Bell.
00:40:22She discovered.
00:40:23That there is.
00:40:24Some periodic source.
00:40:25And this is like.
00:40:26Super strictly periodic.
00:40:27It follows.
00:40:28This.
00:40:29Time.
00:40:30So it's.
00:40:31Every like.
00:40:32One second.
00:40:33You have.
00:40:34A pulse.
00:40:35Like.
00:40:36They didn't see.
00:40:37Previously.
00:40:38Such sources.
00:40:39From.
00:40:40From.
00:40:41From.
00:40:42From the space.
00:40:43So they thought.
00:40:44Maybe.
00:40:45It's.
00:40:46Some intelligence.
00:40:47Some.
00:40:48And they called.
00:40:49This source.
00:40:50I mean.
00:40:51It's kind of.
00:40:52A bit of a joke.
00:40:53Maybe.
00:40:54But they call it.
00:40:55LGM one.
00:40:56Because of.
00:40:57A little green man.
00:40:58And it's for.
00:40:59Some like.
00:41:00Maybe half of the year.
00:41:01The discovery.
00:41:02Was a bit secret.
00:41:03Because.
00:41:04They wanted to.
00:41:05The newspapers.
00:41:06And so on.
00:41:07And actually.
00:41:08Later.
00:41:09Anthony.
00:41:10Huge.
00:41:11Got a Nobel prize.
00:41:12For this discovery.
00:41:13But not just.
00:41:14Well.
00:41:15It was.
00:41:16Controversy.
00:41:17At the time.
00:41:18But.
00:41:19Why people.
00:41:20Associated.
00:41:21With.
00:41:22With.
00:41:23With a neutron stars.
00:41:24Then late.
00:41:25One year later.
00:41:26In.
00:41:27Arecibo.
00:41:28Observatory.
00:41:29Is kind of a huge.
00:41:30Like a plate.
00:41:31In Puerto Rico.
00:41:32A pulsar.
00:41:33And actually.
00:41:34From the crab.
00:41:35Neighborhood.
00:41:36Which we discussed.
00:41:37Before.
00:41:38And they saw.
00:41:39That the period.
00:41:40Is like.
00:41:41Thirty three.
00:41:42Milliseconds.
00:41:43It's like.
00:41:44Super small.
00:41:45And they said.
00:41:46Okay.
00:41:47This should be serious.
00:41:48The source is probably.
00:41:49Associated.
00:41:50Is a receiver.
00:41:51Observatory.
00:41:52In the James Bond.
00:41:53Movie.
00:41:54Or in contact.
00:41:55Just if you were wondering.
00:41:56What to watch.
00:41:57In the evening.
00:41:58But what is the nature.
00:42:00Of such object like.
00:42:01It's like.
00:42:02Very strict pulses.
00:42:03Only thirty.
00:42:04Three milliseconds.
00:42:05It's like crazy.
00:42:06And it's like.
00:42:07Super precise.
00:42:08We will talk also.
00:42:09About this.
00:42:10But then.
00:42:11Since we're talking.
00:42:12About movies.
00:42:13And the Nobel prizes.
00:42:14Of course.
00:42:15Black holes.
00:42:16Are.
00:42:17Very famous.
00:42:18A lot of.
00:42:19Movies about them.
00:42:20But how many.
00:42:21Nobel prizes.
00:42:22Are for black holes.
00:42:23Only one.
00:42:24For neutron stars.
00:42:25Two.
00:42:26Neutron stars.
00:42:27Are more interesting.
00:42:28I'm just joking.
00:42:32So actually.
00:42:33If we.
00:42:34Maybe.
00:42:35Have a stricter.
00:42:36Look.
00:42:37Here's.
00:42:38This professor.
00:42:39Draconi.
00:42:40He also got.
00:42:41Nobel prize.
00:42:42For.
00:42:43X-ray astronomy.
00:42:44And then.
00:42:45This.
00:42:46This was Nobel prize.
00:42:47For gravitational waves.
00:42:48So.
00:42:49This is.
00:42:50Anthony.
00:42:51Hewish.
00:42:52And we will.
00:42:53Also.
00:42:54Talk about.
00:42:55House.
00:42:56Taylor.
00:42:57So.
00:42:58What is the.
00:42:59Nature of this.
00:43:00Source.
00:43:01So.
00:43:02You can suppose.
00:43:03That it could be.
00:43:04Some.
00:43:05Pulsating star.
00:43:06So.
00:43:07It has some.
00:43:08Periods.
00:43:09It pulsates.
00:43:10But actually.
00:43:11What was detected.
00:43:12That the period.
00:43:13Slowly.
00:43:14Slowly.
00:43:15Increases.
00:43:16This time.
00:43:17So.
00:43:18And also.
00:43:19The estimation.
00:43:20So.
00:43:21That the.
00:43:22Period of pulsation.
00:43:23Of star.
00:43:24Should be.
00:43:25Larger than.
00:43:26Two seconds.
00:43:27So.
00:43:28It cannot be.
00:43:2933 milliseconds.
00:43:30If you have some.
00:43:31Rotation.
00:43:32You have some.
00:43:33Frequency.
00:43:34Or read.
00:43:35But there's actually.
00:43:36Limit on the.
00:43:37Rotation.
00:43:38Is like.
00:43:39At some point.
00:43:40The centrifugal force.
00:43:41Can actually.
00:43:42Tear the star apart.
00:43:43It starts.
00:43:44It starts.
00:43:45To be elongated.
00:43:46To the equator.
00:43:47For example.
00:43:48If there is.
00:43:49An axis of rotation.
00:43:50Here.
00:43:51Starts to be elongated.
00:43:52And then some point.
00:43:53It can actually.
00:43:54Even form.
00:43:55Is called.
00:43:56Decretion disk.
00:43:57And some stars.
00:43:58Have it.
00:43:59And then at some point.
00:44:00It can be actually.
00:44:01Blown away.
00:44:02You can obtain.
00:44:03From very simple.
00:44:04Estimations.
00:44:05The limit.
00:44:06So if you just.
00:44:07Calculate.
00:44:08The centrifugal force.
00:44:09Should be.
00:44:10Equal to gravity.
00:44:11Very simple math.
00:44:12You can obtain.
00:44:13What is the frequency.
00:44:15And is equal to.
00:44:16Zero.
00:44:17This is a density.
00:44:18So.
00:44:19If we use.
00:44:20Density.
00:44:21Inside.
00:44:22Wide worth.
00:44:23We will have.
00:44:24Then the period.
00:44:25Should be.
00:44:26Bigger than one second.
00:44:27So it doesn't work.
00:44:28If we use density.
00:44:29Inside neutron stars.
00:44:30Works.
00:44:31And actually.
00:44:32The.
00:44:33Fastest rotating.
00:44:34Pulsar.
00:44:35It's.
00:44:36Very close.
00:44:37To the limit.
00:44:38And it.
00:44:39Frequency.
00:44:40Has.
00:44:41It rotates.
00:44:42Like.
00:44:43Seven hundred.
00:44:44Sixteen.
00:44:45Times.
00:44:46Per second.
00:44:47It's like.
00:44:48And.
00:44:49What is neutron star.
00:44:50Is actually.
00:44:51A huge lighthouse.
00:44:52So.
00:44:53Pulsar.
00:44:54Sorry.
00:44:55It emits.
00:44:56Some radiation.
00:44:57From the.
00:44:58So called.
00:44:59Polar caps.
00:45:00So here.
00:45:01And.
00:45:02When.
00:45:03This radiation.
00:45:04How.
00:45:05What.
00:45:06What.
00:45:07What.
00:45:08What.
00:45:09What is a kind of like.
00:45:10Of you.
00:45:11On what is.
00:45:12Pulsar.
00:45:13The rotating.
00:45:14Newton star.
00:45:15And actually.
00:45:16The spin period.
00:45:17Is extremely.
00:45:18Well known.
00:45:19For example.
00:45:20For crap.
00:45:21Pulsar.
00:45:22Like.
00:45:23It changes.
00:45:24Only in the like.
00:45:2513 digit.
00:45:26Or something like this.
00:45:27But.
00:45:28It's also.
00:45:29Maybe intuitively.
00:45:30Could be understood.
00:45:31And it rotates.
00:45:32You can imagine.
00:45:33It's hard.
00:45:34To stop it.
00:45:35It will rotate.
00:45:36Kind of.
00:45:37With the same period.
00:45:38All the time.
00:45:39And here.
00:45:40Are the pulses.
00:45:41From the.
00:45:42From the.
00:45:43From the.
00:45:44From the.
00:45:45From the.
00:45:46Pulser.
00:45:47And if you.
00:45:48Listen to some music.
00:45:49You may be known.
00:45:50Join the vision group.
00:45:51And they use it.
00:45:52In the album.
00:45:53Yeah.
00:45:54And then.
00:45:55There is actually.
00:45:56Pulser timing.
00:45:57In.
00:45:58In Gdansk.
00:45:59Church.
00:46:00They use.
00:46:01Pulser.
00:46:02As a.
00:46:03Kind of.
00:46:04Clock.
00:46:05Because.
00:46:06Period pulsars.
00:46:07It only changes.
00:46:08Like.
00:46:09No.
00:46:10Precisely.
00:46:11To 10 to the minus.
00:46:1210 to the minus.
00:46:1320.
00:46:14While most.
00:46:15Accurate atomic.
00:46:16Cloaks.
00:46:17Accuracy is.
00:46:1810 to the minus.
00:46:1918.
00:46:20So it's kind of.
00:46:21Comparable.
00:46:2240 billion years.
00:46:23So in principle.
00:46:24We could use.
00:46:25Pulsars.
00:46:26Pulsars.
00:46:27In our days.
00:46:30So why.
00:46:31It rotates so fast.
00:46:32So.
00:46:33You can imagine.
00:46:34That there was a star.
00:46:35Progenitor.
00:46:36It rotated.
00:46:37With some frequency.
00:46:38It has some.
00:46:39Angular momentum.
00:46:40J.
00:46:41Which is equal to.
00:46:42Mass of the star.
00:46:44On the radius of the star.
00:46:45Squared.
00:46:46On the frequency.
00:46:47And if you can serve.
00:46:49Oh sorry.
00:46:50If you compress.
00:46:51This star.
00:46:52To the small ball.
00:46:53The angular momentum.
00:46:54Should be conserved.
00:46:55It means.
00:46:56So this should be the same.
00:46:59But r drops.
00:47:01So then omega.
00:47:02Should raise.
00:47:03So frequency rises.
00:47:05A lot.
00:47:06And it's.
00:47:07Also can be seen.
00:47:08If you watch.
00:47:09Figure skating.
00:47:10If you see people doing.
00:47:11Camel spin.
00:47:12They usually.
00:47:13Rotate kind of slow.
00:47:14And then.
00:47:15If you.
00:47:16They use.
00:47:17This kind of spin.
00:47:18I think it's like.
00:47:19I upright spin.
00:47:20Something like this.
00:47:21It rotates.
00:47:22Much faster.
00:47:23Can imagine.
00:47:25I don't know.
00:47:26If you watch.
00:47:27Figure skating.
00:47:28Me not.
00:47:29How does it emit?
00:47:31What is the.
00:47:32Mechanism for the radiation.
00:47:34Of pulsar.
00:47:35So.
00:47:36It is.
00:47:37To be honest.
00:47:38Not well understood.
00:47:39I mean.
00:47:40There are models.
00:47:41But it's not like.
00:47:42There is one standard model.
00:47:44For pulsar radiation.
00:47:45And still.
00:47:46From the 70s.
00:47:48It's not like.
00:47:49People.
00:47:50Did all the work on this.
00:47:52They are.
00:47:53Working very hard.
00:47:54But it's.
00:47:55It's.
00:47:56It's really complicated.
00:47:57But it kind of like.
00:47:58I will give you.
00:47:59Some naive.
00:48:00Naive picture of this.
00:48:01So imagine.
00:48:02There is a magnet.
00:48:03Which.
00:48:04Rotates.
00:48:05So here.
00:48:06And this.
00:48:07Magnet axis.
00:48:08Is not aligned.
00:48:10With a rotational axis.
00:48:12That's why.
00:48:13We see this pulses.
00:48:14So it rotates like this.
00:48:15Here.
00:48:16Then the.
00:48:17Rotating magnets.
00:48:18Actually generate currents.
00:48:20And currents.
00:48:21Pull out.
00:48:22Particles.
00:48:23From the neutron star surface.
00:48:24Here.
00:48:25Kind of electrons.
00:48:26Maybe protons.
00:48:27Are pulled out.
00:48:28And then they move.
00:48:29On these.
00:48:30Magnetic field lines.
00:48:31Here.
00:48:32You see.
00:48:33And at this point.
00:48:34They.
00:48:35They.
00:48:36Radiate a lot.
00:48:37Here is like.
00:48:38The radiate.
00:48:39Some.
00:48:40Photons.
00:48:41And then.
00:48:42These photons.
00:48:43Actually can be.
00:48:44Absorbed.
00:48:45And can create.
00:48:46Again.
00:48:47Electron.
00:48:48And positrons.
00:48:49So they.
00:48:50There is called.
00:48:51A cascade.
00:48:52Mechanism.
00:48:53There.
00:48:54Electron.
00:48:55It means photons.
00:48:56But then these photons.
00:48:57Create.
00:48:58More and more.
00:48:59Electrons.
00:49:00And positrons.
00:49:01So we have.
00:49:02Electron.
00:49:03Positive plasma.
00:49:04Which emits.
00:49:05Here.
00:49:06Some.
00:49:07Magnetic field lines.
00:49:08Here is.
00:49:09The field.
00:49:10Of the neutrons.
00:49:11Magnetic field.
00:49:12Of the neutron star.
00:49:13And it's all.
00:49:14Filled.
00:49:15With.
00:49:16Electron.
00:49:17Positron.
00:49:18Plasma.
00:49:19And this is.
00:49:20How it looks like.
00:49:21Here's.
00:49:22Jets.
00:49:23Coming from it.
00:49:24And this is called.
00:49:25Pulsar.
00:49:26Nebula.
00:49:27So.
00:49:28And what we can learn.
00:49:29From this period.
00:49:30So.
00:49:31Pulsar.
00:49:32Is rotation powered star.
00:49:33And energy loss.
00:49:35Due to the radiation.
00:49:36Causes pulsar.
00:49:37To spin down.
00:49:38Because it emits.
00:49:39A lot of energy.
00:49:40So it's kind of.
00:49:41Like a dipole.
00:49:42And then it.
00:49:43Kind of.
00:49:44Rotates.
00:49:45Slow.
00:49:46And slower.
00:49:47And slower.
00:49:48And then the spin down rate.
00:49:49Which is called.
00:49:50P dot.
00:49:51So it's a derivative.
00:49:52So change.
00:49:53Of the period.
00:49:54With time.
00:49:55Is actually.
00:49:56Proportional.
00:49:57To the magnetic field.
00:49:58So the higher.
00:49:59Is magnetic field.
00:50:00Of the neutron star.
00:50:01The faster.
00:50:02It slows down.
00:50:03Actually.
00:50:04So if you have.
00:50:05A neutron star.
00:50:06With a huge magnetic field.
00:50:08For example.
00:50:0910 to the 15 gauss.
00:50:10Here are red points.
00:50:11They're called.
00:50:12Magnetars.
00:50:13Because they have.
00:50:14A huge magnetic fields.
00:50:15Well in comparison.
00:50:16To the sun.
00:50:17Or.
00:50:18I think the largest field.
00:50:19Recreated on earth.
00:50:20In some explosion.
00:50:21Experiments.
00:50:22Was.
00:50:2310 to the 6 gauss.
00:50:24At maximum.
00:50:25And magnetars.
00:50:26Have like.
00:50:27Much.
00:50:28Much.
00:50:29Higher fields.
00:50:30You can.
00:50:31See.
00:50:32That their.
00:50:33Period derivative.
00:50:34Is larger.
00:50:35These are.
00:50:36Normal pulsars.
00:50:37Here.
00:50:38Here's a period derivative.
00:50:39And here's a period.
00:50:40On the star.
00:50:41And here.
00:50:42Millisecond pulsars.
00:50:43Which are.
00:50:44Oh.
00:50:45Just rotates.
00:50:46Very very fast.
00:50:47From this diagram.
00:50:49You can also obtain.
00:50:50What is the characteristic.
00:50:51Age.
00:50:52Of the pulsar.
00:50:53So we can just.
00:50:54Estimate it.
00:50:55From.
00:50:56P.
00:50:57Divided by.
00:50:58Divided.
00:50:59You can.
00:51:00Easily obtain it.
00:51:01And here.
00:51:02Is shown.
00:51:03This is.
00:51:04This is kind of.
00:51:05The age.
00:51:06Of the pulsar.
00:51:07So we can.
00:51:08Estimate.
00:51:09That the magnetars.
00:51:10Are usually.
00:51:11Yeah.
00:51:12Neutron stars.
00:51:13With like.
00:51:1410.
00:51:15Thousand years.
00:51:16But these.
00:51:17Millisecond pulsars.
00:51:18Are usually.
00:51:19Old.
00:51:20Neutron stars.
00:51:21Estimate.
00:51:22What is the age.
00:51:23Of the neutron star.
00:51:24And actually.
00:51:25You can compare it.
00:51:26To the.
00:51:27It's called.
00:51:28Kinematic age.
00:51:29Or something like this.
00:51:30If you.
00:51:31Know.
00:51:32For example.
00:51:33For crap.
00:51:34We know.
00:51:35The year.
00:51:36When it explodes.
00:51:37And then we know.
00:51:38About how.
00:51:39How moves.
00:51:40Its envelope.
00:51:41From the neutron star.
00:51:42And then.
00:51:43Just from the moving.
00:51:44Envelope.
00:51:45We can estimate.
00:51:46When it was in the center.
00:51:47And obtain.
00:51:48And the age.
00:51:49Of the pulsar.
00:51:51Two months.
00:51:52Yeah.
00:51:53You're right.
00:51:54Ju Pitter is.
00:51:55Pulsar.
00:51:56But.
00:51:57What is usually.
00:52:12neutron star.
00:52:13But the same mechanism.
00:52:15Would be applied to.
00:52:16Jupiter.
00:52:17Or to whitework.
00:52:18They also have pulses.
00:52:19not as bright as neutron stars so what this code usually puts us a neutron
00:52:26star but in principle the mechanism you're absolutely right could be applied
00:52:30to any kind of like charge ball with currents and so on rotating okay we go
00:52:38and there is actually a huge zoo of neutron stars so people try to it's
00:52:43called like a grand unification theory for all neutron star people try to do
00:52:48population synthesis and really predict for example why neutron star was born
00:52:53there and then maybe it is connected and it became older and came here and then
00:52:58came here so people try to connect and so on so these on top are called magnetars
00:53:04these X-ray isolated neutron stars with the orange things there are seven known
00:53:13sources it's called Magnificent Seven and maybe there are all magnetars and there
00:53:19are also like new fast radio burst sources there are now a lot of things and I mean
00:53:26a lot of papers on this and they associated with a huge explosion maybe in
00:53:31the magnetosphere of the neutron star is connected to large magnetic field and so
00:53:36on but it's not like proven that they come from the neutron star there are other
00:53:40theories and so on actually I think their first was they were detected in Australia
00:53:47and there was also a story about this that people saw some sources with some
00:53:53periodicity and the telescope but it was coming kind of from everywhere and they
00:53:57didn't understand like what is the source of this it turned out to be microwave
00:54:01actually some people were just cooking their lunch and yeah there was it's
00:54:08called plerion periton sorry periton discovery and here is a millisecond pulsars
00:54:15and actually they are very old but fastly rotating and it's exactly because they
00:54:21are or they were in the binary system where the matter accreted matter was
00:54:27accreted on top of the neutron star so it's kind of like orbital momentum of the
00:54:33system was actually transferred to the neutron star rotation so all this
00:54:38accretion disk if you if you squeeze it on the neutron star then it kind of spin it
00:54:43up that that is the theory of millisecond pulsars so there are a lot of
00:54:48different Newton stars and so on I will not talk in the big detail about this
00:54:53which it's already seven so just maybe five minutes more what is now what is
00:55:02going now in the field there is a nicer x-ray telescope it's on the
00:55:06International Space Station you can see at the moment that it was installed on
00:55:11the on the space station and here how it looks like and it detects x-ray
00:55:18emission from the neutron star surface yeah here you can see so if you imagine
00:55:24some hotspot on the neutron star so here the yellow thing and then it rotates and
00:55:31then it gives you kind of the pulses of the on the hotspot you will see the
00:55:35brightness with time but actually neutron star super compact object that is the
00:55:41most compact object in the universe that has a surface that you can step on black
00:55:47holes they are of course more compact but you will die if you step on it so
00:55:52there is no kind of surface that I stopped the movie stopped so and then but they have a huge
00:56:00gravity doesn't play so they have a huge gravity and that gravity actually man's kind of the the photons
00:56:12coming from another side so actually you can see a bit of another side surface of
00:56:18the neutron star you can see it here so photons coming for example I'm staying
00:56:22here I'm emitting for example photon there but if I had a huge gravity it would
00:56:27bend and then arrive to you that is what going on here but then with this thing you
00:56:34can actually estimate the compactness of the neutron star and you can obtain some
00:56:38estimation on radius and mass of the neutron star and that's how these contours for example
00:56:44these are these are neutron star these contour contours are constructed so you can have like
00:56:50the mass and radius should be in this range or in this range on here and that is usually juxtaposed
00:56:56or compared to two theoretical models so good model should go through these contours here and it's now it's a very big thing in the field but unfortunately
00:57:10nice here is not more working anymore but maybe we'll have another telescopes in the future and the other thing is actually
00:57:17Pulsar rotates like kind of with the same frequency so on but then people observe that there are actually sudden glitches in the systems
00:57:25so neutron star for example spin down slowly slowly spins down and it's everything looks fine but then suddenly it increases its rotation and then start to decrease again
00:57:35this is called glitch mechanism this kind of like interrupted in the rotation and they're possibly associated actually with interaction of the superfluid component
00:57:46in the neutron star and the normal component in the crust so superfluidity means that something flows with zero viscosity so for example here you have liquid helium at very low temperature
00:57:58like 2 kelvin or something like this or minus 270 celsius and if you if you have something with a liquid helium it will start to leak here and then some drop will condensate
00:58:13state it and move for here so because it has kind of no viscosity and the same thing can occur in the neutron stars but at much much larger temperature
00:58:23because it has high much higher density so the neutrons can be superfluid and then if you rotate your superfluid you will create some kind of vortices of the matter
00:58:35and then they have some angular momentum then the neutron star spins down but it's kind of the crust of the neutron star spins down
00:58:42but the vortices they they have no viscosity so they do not interact imagine and then they they continue to rotate with their own angular momentum and then in some point also not well understood
00:58:54they can transfer the angular momentum to the crust and accelerate it so suddenly the transfer and the crust is accelerated that's why there is a huge jump here and then it slows down again so this is another interesting mechanism
00:59:10mechanism in neutron stars
00:59:14and here's the internal structure of the neutron star and with different models so you can have like neutrons protons electrons and muons which is kind of like a bit boring scenario but then you can also have quarks
00:59:28so quarks this is what uh is uh nucleons are composed of if you look at the your uh neutron proton it will be composed of up and down quarks
00:59:38so it could be strange quarks some like mesons that are also made of quarks and so on there is a a large variety of the models so neutron star can be more than just neutrons
00:59:50neutrons there is also hypothesis of the quark stars which are composed of uh three quarks here but they're not discovered also a lot of speculations are uh going around about them
01:00:04so i will probably stop here because it's already one hour we have and uh i will be happy to answer your questions
01:00:18yes please
01:00:24uh yeah they do not kind of die but there is yeah there's kind of like uh the death line or something
01:00:38like this on the pp dot diagram uh here usually indeed this mechanism is working when you have high magnetic field
01:00:46and you have a lot of rotation actually the fact is magnetic field decays because these currents
01:00:53that are that the the flow in the in the neutron star crust there is like kind of like omic dissipation
01:00:59so the energy goes to heat magnetic field decays neutron star also slows down at some point they stop
01:01:05emitting radio emission so not all neutron stars are pulsers some of them can be very old and the mechanism is not working in it
01:01:23actually spinning
01:01:33emitting and like the like the magnetic poles or are some just like not spinning and just normal neutron stars
01:01:43or even just like they all all neutron stars emitted the poles and just some we can see them because like the pole is well
01:01:51turned towards us and already is impossible yes yes you are right that there is some selectivity effect
01:01:58that you see the neutron star it rotates it indeed there is some kind of like a cone of emission but you
01:02:05cannot see it just because it goes not directly at you yes so of course there is this thing so because this
01:02:14this radiation is quite actually concentrated there is kind of an angle of around like 10 degrees here
01:02:22but there is also x-ray emission which is broader actually and then there are other mechanisms on
01:02:29and indeed some of the neutron stars we cannot see pulses because of them but also
01:02:34for some of the neutron star this mechanism would not work uh anymore so not all neutron stars are pulsers so yeah
01:02:44uh uh probably yes because uh they have rotation magnetic field and so on so
01:02:51should be like this in general but of course there are maybe some exceptions and so on but in principle yeah
01:03:02yes please
01:03:07yes in principle uh yeah i forgot that i need to repeat the questions every time
01:03:14yeah yeah yeah yeah it's better maybe so yes indeed uh if you create a lot of matter or neutron star
01:03:25it can uh it can collapse and then we will next time discuss what will happen if two neutron stars collide
01:03:32it can also happen and then they can create hypermassive neutron star that is kind of
01:03:38uh sustained by fast rotation because of centrifugal forces but then the rotation uh slows down and it
01:03:47collapses to the black hole
01:03:55you
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