Daniel and Jorge Explain the UniverseDaniel recounts the story of how pulsars were discovered and what they tell us about the death of stars.
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What is the moment of scientific discovery? Actually, like I mean in the movies, it always seems so crisp scientists find something in her data or an experiment, Suddenly it dramatically works. We go from ignorance to knowledge in a moment, from failure to success that kind of drama works for the movie screen, but how does it happen in real life? Is it a slow and steady march rather than a sudden leap, or are there actually real moments of insight where all of a sudden light penetrates the darkness and the scientists learn something new about the universe that no human has ever known before. Hi, I'm Daniel. I'm a particle physicist and I've been doing particle physics experiments for decades but never discovered a new particle. And welcome to the podcast. Daniel and Jorge explain the Universe, in which we examine everything about the universe, from its origins to its ends, from its biggest things to its smallest things, from all of its mysteries and all of our discoveries. Our goal in this podcast is to open our minds to all of the craziest, biggest, deepest, most important questions, the one that frame the context of being human, the ones that tell us what it means to be in this universe and how this universe works. We tackle all those questions and we go right to the forefront of scientific knowledge. We take you right to the edge where scientists are currently working can we explain all of it to you in a way that we hope makes sense and maybe even occasionally makes you laugh. My co host, Jorge Tam the Creative PhD Comics, can't be here today, so I'm going to share with you one of my favorite stories of scientific discovery. And I mentioned earlier on that I have never discovered a new particle. That's not one hundred percent true. My career in particle physics spans from the mid nineteen nineties till today, and in the mid nineteen nineties was the discovery of the top quark. Jorge and I did a really fun episode about that whole amazing, hilarious, dramatic story. But I sort of joined the field right when that had already happened, so I wasn't around when the top quark was discovered. I didn't get to participate in that moment of discovery. I was, however, part of the team that discovered the Higgs boson. But you have to understand, this was a really big group of people, thousands of thousands of people who all contributed little bits here and there, and there wasn't really a dramatic moment when we said, aha, the Higgs is there. It solely emerged out of the data, sort of the way a treasure chest might be revealed in the sand of a beach, as a tide pulls out inch by inch, showing you more and more of it. That was sort of the way the Higgs Boson discovery went. We saw a little peak, we thought it might be it. It got bigger and bigger and bigger, and there was never really a moment other than the official announcement when we could say, now we have discovered the Higgs. But that sort of was a bureaucratic choice and artificial choice. There was no single aha moment. And part of that is because we knew what we were looking for. We suspected the Higgs was there, we knew how to find it, we knew how to look for it, we knew what to expect, and so when we saw it, it was just sort of this slow creeping realization that we had found what we had been hunting. But that doesn't mean it's always like that. There are moments of discovery in science. Usually they happen when we're more surprised, when we see something we didn't expect. When you go looking for one thing and you find something else moments, for example, like the discovery of the cosmic microwave background that we talked about a few episodes ago. Today, we're going to tell the story of one of those moments when discovery came quickly, when someone went looking for one thing and found something else, something alarming and astonishing, a moment of insight about the universe. Actually, we're going to tell a story of two of those moments, because this discovery has multiple parts, and for one of those parts, we happen to have real historical audio of those scientists realizing their discovery in real time as it happens, so you'll get to hear what it actually sounds like when scientists are astonished when they make a real life discovery. So that's super fun, and for me, it's always really interesting to try to understand what it was like to make that discovery. You know, it's easy in hindsight to say, oh, these things exist, here's how you look for them. That when did it badaboom but a being done. But you have to go back to what it was like before we knew it was there, to put yourself back in that mental position of ignorance, not knowing whether something is out there, not understanding whether you live in the universe where it's real or where it's just an idea, not knowing which direction human knowledge and science will take. Science is so easy in hindsight and so difficult in foresight. When you stand in the forefront of human ignorance, you don't know necessarily which way to go. So it's really valuable to revisit these moments when we took a step forward, when we went from ignorance to knowledge, and understand what was required, how it happened, and the bravery it took to make that claim to say I have found something new. I now know something about the universe that no human ever knew before. And so today we're going to be telling one of my favorite stories of discovery, one about a really weird kind of star, a very fast, very dense, very bizarre kind of star that we've talked about on the podcast. And so today's episode we'll be answering the question how were pulsars discovered? And so, as usual, before we dig into the topic and tell you the story today, I wanted to know how much people already knew about this sort of famous story. So I went out and solicited volunteers from the answernet to tell us what they knew about various questions in science, of this being one of them. So thank you to all of those who participated and give us their speculation without the opportunity to look into any reference material whatsoever on the honor system. Of course, if you'd like to participate and hear your voice on the podcast in the future, please don't be shy. I promise you it's fun. Send me an email to questions at Danielandjorge dot com. But in the meantime, think to yourself, do you know the story of how pulsars were discovered? Here's what people had to say. I am eighty percent sure that were discovered when they stuck a stethoscope onto the Hubble space telescope.
I'm guessing pulsars were discovered by scientists who observe these stars that were kind of flashing, so dimming and brightening in these regular pulses. Hence the name pulsar. I realized I just described what a pulsar is, not how they were discovered, So sorry about that.
For what a pulsar is, I would say it was discovered as a rapidly blinking source of light in the sky.
They were discovered by I think she was a graduate student in the sixties. Something they were they discovered through listening to some radio signals, and first they thought it was EXTRATRACI in life, because they called that little Green Men LGM.
But I always confused pulsars and quasars. I'm going to guess that someone saw repetition of light in some part of the sky over and over and that led to an investigation that found the pulsars.
Pulsars were discovered by a woman, and I believe it was in the nineteen seventies, but I'm not sure how or why or where even.
There was a woman astronomer, radio astronomer whose name, unfortunately I cannot remember, was doing some sort of sky survey when she noticed a set of pulses that were incredibly regularly spaced. She actually annotated them as LGM for little Green men. One time they thought it might have been discovery of aliens, but later they discovered that it was actually a rotating neutron star and the magnetic field was exciting the gas molecules around it and giving off radio energy.
All right, So congratulations to our excellently informed listeners together, they really do have most of the story there. There's a lot of really insightful stuff and a lot of bits of the story are there in pieces here and there. So let's dig into it and to really understand how pulsars were discovered, we have to understand, of course, first what a pulsar is, how we came to the idea of it existing in the universe, and that'll help us understand how it was seen and how we knew what we were seeing. All right, So first of all, what is a pulsar. A pulsar is a very very compact object. Neutron stars and white dwarfs are more famous as the sort of like densest things in the universe, and a pulsar is a version of these. It's most commonly considered to be a version of a neutron star, but it can also be a white dwarf, but both of them essentially are the end points of stars. Stars have these incredible life cycles where you start out as a big molecular cloud, huge blob of gas and dust that's somehow shocked to collapse into a hot and dense object, a star which burns for billions and billions of years in this incredible, incredible balance between gravity that's pulling it together, trying to turn it into a black hole or something very very dense, and fusion which is erupting and sending radiation out to prevent the collapse of that star. And it always amazes me that these things go on for so long, these two cosmic forces so different, both so powerful, can be so balanced for so many billions of years. Well, at some point the star gives up because it's burned most of its fuel and its core has become very very heavy and filled with things that it can no longer fuse. When the core of the star is filled with iron, for example, fusing iron doesn't generate heat, it actually costs energy, so it cools the star. So now the star no longer has that power from fusion to resist gravity, and it collapses. There's some intermediate stages in there we'll skip over, such as it becoming a red giant. But depending on the size of the star, this collapse generally triggers a supernova. So you have this collapse with the materials racing inwards, which then causes that back reaction outwards, a massive explosion where a huge chunk of the stuff that used to be the star is now spread out into a new nebula, like a big sprawling cloud of gas and dust. At the core of it, however, is a very dense, very hot remnant, and that remnant can either be a white dwarf or a neutron star or a black hole, depending on the mass of the original star. So smaller stars end up as white dwarfs, which are basically just like huge hot chunks of metal that are resisting collapsing because there are fermions and they don't like to overlap too much. Or if they are larger, they become neutron stars, where gravity now pushes them together and forces all of the protons and the electrons together into forming new neutrons, and you have this really weird material that's sort of like the nucleus of an atom, but the size of a mountain, So it's incredibly dense, incredibly weird stuff, something we even still today do not understand in detail. And then, of course, if the star is more massive, it would become a black hole. So the gravity totally wins and nothing prevents the collapse and it becomes a black hole. But it's the first two categories that are more interested in. And let's focus on the neutron star category because that's the majority of pulsars. So you have this very dense object, right, and the object is a huge chunk of the material that used to be a star, not all of it. Some of the material is lost in the supernova and some of it remains in this cloud that surrounds the neutron star. But this neutron star is a very very dense object and very very small because gravity's really pulled it together. And what that means is that it's spinning really fast. Why is it spinning fast, Well, the star itself was spinning because everything in the universe is spinning. And the reason is simple is because angular momentum is conserved. You know how momentum is conserved. If you push on something, it stays in motion until something else pushes on it. Or if you don't push on something, it stays still until something does push on it. That's conservation of momentum. Those are Newton's laws. Well, there are similar laws for angular momentum. That is that something spinning tends to keep spinning. And to make something spin, you got to give it a push. So if you leave something alone, it will keep spinning the way it's always been spinning, right, that's conservation of angular momentum. And so the original gas cloud that formed that star had some spin to it, and that spin can't go away. It needs to stick around. And as the gas cloud gets smaller and smaller and turns into a star, the star spins faster. Now that might sound like it violates conservation of angular momentum because it's spinning faster, right, Well, the velocity of the stars spin is not what's conserved. It's the angular momentum, which is the product of the velocity and their radius. So things that are larger spins slower with the same angular momentum is things that are smaller than spin faster. You know this because if you're a figure skater and you pull your arms in, you spin faster. You have the same angular momentum. You're not pushing against anything to spin faster, but you spin faster because your radius is smaller. So to have the same angler momentum, you gotta go faster. That's why the star spins faster than the original gas cloud. And that's why the super compact, dense, little neutron star that has a huge chunk of the star's mass, but is much much smaller. We're talking about something only kilometers in size, you know, maybe ten fifteen kilometers has to be spinning really really fast to have the same angler momentum as most of the original star. So that's why these things are spinning so fast, because they are so small, because they are so dense. In addition, some of these things are highly magnetic. There's a magnetic field of these stars, just like every star and most planets have a magnetic field, and that's because the motion of charged particles inside it. A neutron star is mostly neutrons, but there are protons and there are electrons, and they are moving around sometimes on the surface, and the flux of the particles on the inside can create these magnetic fields. So you have this object that's spinning really really fast and it has a magnetic field. In addition, it's generating a huge amount of radiation. The magnetic field of the thing is rotating, which generates an electric field which accelerates the protons and the electrons on the surface of the neutron star, and that creates a bunch of radiation because when you accelerate particles they radiate photons. So you have this magnetic fields on this neutron star that's rotating and is generating an electric field which pushes the electrons and protons on the surface of the star, creating a lot of radiation. Radiation doesn't go in every direction because there's a strong magnetic field. That radiation tends to go along the magnetic north and the magnetic south because magnetic fields are really good at bending the path of charged particles. The reason that we don't get a lot of radiation from space is because we have a magnetic field here on Earth, and when particles come from space, they are bent around those magnetic field lines. The magnetic field lines are sort of like the lines on a basketball, right they run from north to south, and if a particle comes from space, it gets bent by those magnetic fields and goes out in another direction where sometimes they loop around those magnetic field lines all the way up to the north or the south pole, and then they can slip in between the magnetic field lines. And that's, for example, why we have the northern lights and the southern lights, because magnetic fields guide charged particles in the same way. If you generate radiation on the surface of the planet. It's also bound by those magnetic fields, and so in this case, the magnetic fields are even much more powerful, and essentially all of the radiation from the neutron star gets guided towards the north or the south pole of the magnetic field. So you get these beams of radiation shooting off of this crazy neutron star. Right Like it's not crazy enough, it's already super hot, super dense, super small, spinning, super fast, really magnetized, and now on top of that, it's shining these two crazy flashlights out into the universe, one from its magnetic north pole and the other from its magnetic south pole. And these beams don't come for free. They are very bright. They cost a lot of energy, and this energy comes from the spinning of the neutron star, because that's what's generating this electric field, the rotation of the magnetic field, and eventually it's going to slow it down, like these pulsars. They generate these beams and they last for maybe ten or one hundred million years, but they don't last for their whole lifetime. At some point, the beams turn off because the neutron star has slow down and it's not generating that radiation anymore. What that means is that for most of a lifetime, the pulsar is actually quiet. They don't emit these beams, and so something like ninety nine percent of the pulsars out there aren't actually emitting any radiation anymore. They are quiet. The universe is filled with dead pulsars, pulsars that have gone quiet. So we've explained what a pulsar is and how it emits these beams. But why do we call it a pulsar? Are these beams themselves like pulsing? Do they turn on and off? Now, the beams don't turn on and off. I mean, they last for millions of years and they eventually fade, but they don't like flicker on and off. The reason we call it a pulsar is because we only see those beams as they pass by the Earth, because the beam is shooting up and down along the magnetic field lines. But that's not necessarily the same as the axis that the pulsar is spinning around. So if it were, if the magnetic north and the magnetic south were the same as the north and south of the actual star, so spinning around the north pole, then it would always be shooting the beam north and a beam south. However, if instead the magnetic field is tilted so that it's like spinning along one axis, but its beams are shooting off a little bit skewed, then when it spins around, the direction of that beam changes right. It's like if you're holding a flashlight and you point it straight up and then spin, the direction of the flashlight doesn't change. But if you hold a flashlight straight out and then spin right, then what happens. Then your flashlight's going to sweep around three hundred and sixty degrees every time you rotate. And what if somebody see if they are standing in front of you watching you spin, they see a flash. They see a pulse of light only when the flashlight is pointed in your direction. So it's this difference between the direction of the pulsar's magnetic field and its actual spin axis, which makes it a pulsar, right, That's what makes it appear to pulse. They don't actually pulse. They're sending bright streams of light continuously out into the universe until they fade. But we see them pulsing because that beam sweeps across Earth, and that's what we see. So that's what a pulse are is an introduction to these weird things in the universe. Next, we're going to talk about why we suspected they might exist and how they were actually found. But first let's take a quick break. With big wireless providers, what you see is never what you get. Somewhere between the store and your first month's bill, the price, your thoughts you were paying magically skyrockets. With mint Mobile, You'll never have to worry about gotcha's ever again. When Mint Mobile says fifteen dollars a month for a three month plan, they really mean it. 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Take water, for example, most dairy farms reuse water up to four times. The same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US Dairy tackling greenhouse gases? Many farms use anaerobic digestors that turn the methane from maneuver into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love with less of an impact. Visit usdairy dot com slash sustainability to learn more. All right, we're back and we're talking about the incredible story of the discovery of pulsars. And we reminded ourselves that pulsars are tiny, very hot, very dense, very quickly spinning stars the left over heart of a supernova. They're shooting a beam of light out into the universe, and they are also spinning, and so that beam of light passes over the Earth and looks like pulsations. It looks like pulses from something out there in the universe. And before we discovered these things, we had a suspicion that they existed. People have been thinking about the life cycle of stars, and in nineteen thirty four people suggested that when you had a supernova, it might not all blow out into the universe, that you might get this small, dense core left over, and if so, it would have this really weird state of matter. These neutrons would form. They would be in a really dense state, this thing that is sort of like nuclear matter. This in the heart of atoms, but now on the size of a mountain, something kilometers wide. Imagine that the nucleus of an atom, but kilometers wide. So this was a novelty, but nobody had ever seen one before. We didn't know if neutron stars existed in nineteen thirty four, and they would be difficult to detect because these things don't have fusion anymore. They don't glow the same way that very bright stars do, so to see neutron stars seem like a puzzle. But then decades later people said, well, you know, they might have very strong magnetic fields, and if so, they might be rotating, and if so, then they might be pulsing. And so this idea sort of came into existence in the sixties, the idea the pulsars as weird, spinning, magnetized, beaming light neutron stars might be out there. But you have to remember that there are lots of crazy ideas for what might be out there. The astronomy literature is filled with people speculating maybe these things exist, maybe boson stars exist, maybe these other things exist. Now, with a hindsight of history, we can go back and trace the development of this one thread of an idea that turned out to describe something in the actual universe. But don't forget it was buried at the time in a forest of other crazy, wrong ideas about what might be out there in the universe. You know, pulsars exist, and if you took a time machine back to the sixties, you might say, I know these things exist, and I know how to find them. It's not actually that hard. But without the hindsight of that history, of course, it's hard to pick the wheat from the chaff. So let's get to the story of how they were actually discovered. They were found by a graduate student at the University of Cambridge, a woman named Jocelyn Bell, and she was not looking for pulsars. In fact, she wasn't looking for stars at all. She was trying to study quasars. Quasars are at the heart of really large galaxies. They are the accretion disks around black holes, the stuff that has not yet fallen into the black hole but is swirling around. And because of the tidal forces and the incredible gravity, these things get really hot and they radiate a lot of light. And we had seen these things, and we knew that they were very very far away because these quasars have existed for a long time. They were formed in the very early universe, like a billion years after the Big Bang. But they're still super duper bright. And for a long time there were big mystery because people thought, well, what could it be that it's so incredibly bright and so far away, so at its source, it's got to be like mind bogglingly bright. What could that even be? People thought for a long time, this was a mistake. It's not even really a thing. We must be misunderstanding how these things work. And Jocelyn Bell was trying to understand these quasars. She was trying to understand how these quasars twinkle, how they scintillate. You know that when you look at a star in the sky, you see a twinkling, and that's mostly because the stuff between you and the star is interfering with the star light. That's why planets, for example, don't twinkle, but stars do, because the light from the star has to go really really so quoasars kind of twinkle as well. They do this thing called scintillation, and it's due to fluctuations in the densities of particles in the solar wind. So the way we see quasars is not by looking usually at visible light, but by looking at radio waves. These things come from really really far away, and with they're best seen in the radio spectrum. And in the radio spectrum, an obstacle is the solar wind. Remember that the Sun doesn't just shoot out photons. It also shoots out a bunch of charge particles, protons and electrons and other crazy stuff, and this is what we call the solar wind. And when a radio photon enters our solar system from somewhere really really far away, it hits this barrage of radiation coming from the Sun and interacts with it. It's radio signal made of light and electromagnetic radiation. Essentially, photons comes from these quasars billions of years away. They sometimes get deflected or interfered with by these particles in the solar wind, and so that's what makes these quasars scintillate. So she wanted to study this because she wanted to understand koisars. People at that time didn't know that black holes were real, so they didn't know what was powering these quasars, what could possibly be generating so much radiation from so far away. So she built a radio telescope. And a radio telescope is just a bunch of antennas. But the thing about radio waves is that their wavelength is very very long. They could be meters or hundreds of meters. So to capture a radio photon, you need a big antenna, You need something large. So she built something which was four and a half acres, like this thing is big. She spent two years and for her, doing astronomy meant every day pounding fence posts into the ground and stringing wire among them. Imagine one of those old fashioned TV antennas. It was like a grid of metal that could capture a signal. That's essentially what she built. And she strung one hundred and twenty miles of wire over two years to build her radio telescope to capture this signal from these quasars to look at them scintillating. She wanted to see the fluctuations in these signals. And that's really key because what she did is get these radio signals and look at them and develop her own personal sense for what this data should look like. She was looking for characteristic wiggles changes in this data as they study the pulsar. And this is back in the day before they had computers and before people could just like you know, dump the data onto the screen and analyze it bump, bump bump. Her data came out directly onto a printer like her radio telescope capture. This turned it into an electrical signal which would directly send to a printer which dumped it onto paper. So her output from her telescope was stored on one hundred feet per day of printer paper, which is like came out steadily and she would stand there and look at it. She would get to know it. She was like a natural neural network where she learned, oh, if I'm looking over here, then I'm going to see this thing before pointing at the sun, that I'm going to see this kind of radio wave. And this is the kind of thing that she could easily point right. This thing is just something you build in the ground, but the Earth turns, and as the Earth turns, this thing is essentially pointed in a new direction. She herself is like sweeping her instrument across the sky, examining different parts of the universe. And you can get some directional information from a radio antenna based on like when the signal arrives, does it arrive first on the eastern part of the antenna or first on the western part of the antenna. But it's not great at telling where something is coming from exactly. So she became really good analyzing these signals. And then one day, November twenty eighth, nineteen sixty seven, she saw the signal that she did not understand, something she had never seen before. What she saw were pulses separated by one and the third seconds, So it was like boop boop boop, and she would get these pulses of radio waves and the regularity of it. The exact distance between the pulses is what made it seem weird. And at first she thought, oh, this must be a signal from something here on Earth, because of course there are lots of sources of radio waves here on Earth. Almost everything we do with our electronics generates radio noise. Every time you turn on your television, certainly every time you use your cell phone, and of course there are radio transmitters all over the planet. And so first she had to rule out various sources of human interference, like other radio astronomers, people sending pulses off the Moon to measure the distance to the Moon, television signals, beeps from orbiting satellites, even like you know, possible effects from large corrugated metal buildings near the telescopes. She went through this whole list, and you got to do that when you see something weird in your data, you got to first look for the boring explanation like, oh, well, maybe I'm just measuring what happens when somebody turns on the microwave in the breakroom or something like that. You don't go straight to I've discovered something new in the universe. So she very carefully went through all these different explanations and eventually even borrowed somebody else's radio telescope to confirm her observations. She wanted to make sure it wasn't just like some weird blip in her telescope. So she knew it wasn't just her telescope. She ruled out all sources of human earth bound interference, and she saw that it tracked with a particular location in the sky. And that's a great clue that tells you that it's not from Earth, because if it's from Earth, then it doesn't matter which direction the Earth is pointed. If it's not from Earth, then you will only see it when the Earth is pointed in a certain direction, only when the message itself sweeped across your radio telescope. So where do their minds go. The strange regularity of it, the fact that it came like every one and a third seconds, made them think not of some new astrophysical object, because nature is not often that precise, right. Nature is messy. When you go out into the world, you don't see like rocks that are exactly square. You don't see like ten rocks exactly the same size you don't see this sort of regular patterns. I mean, sometimes you do in crystals and in other places, but nature is more often messy than precise and regular. So their media thought was like, wow, maybe this is alien intelligence. You know, she says quote. We did not really believe that we had picked up signals from another civilization, but obviously the idea had crossed our minds, and we had no proof that it was an entirely natural radio emission. It is an interesting problem if one thinks one may have detected life elsewhere in the universe, how does one announce the results responsibly? So they really didn't know what they had. They were wondering, is this something weird and knew? Are these aliens? Or is this some natural source of radio emission that's weirdly regular. So in their internal notes they called this thing LGM, one for little Green Men. And so here you can see the process of discovery in motion. Like there existed in the literature, the speculation that these things might be out there, that spinning neutron stars might generate pulses, and here they are discovering pulses in the radio spectrum, essentially exactly what was predicted. But they couldn't put it together, because, as we mentioned before, there are lots of predictions out there in the literature, only in hindsights you know exactly who to listen to. It's like picking one of Nostrodamis's predictions, right. Most of them are nonsense, and if you look back to all of them, you can always find one that seems to make sense. So what they did was they kept looking, and pretty soon they found another pulsar somewhere else in the sky, and that told them, m it's probably not aliens, because there are signals coming from two very different, very distant locations in the universe, so probably it's a natural source. And then by Christmas of nineteen sixty seven, right just like weeks after the first discovery, they had found four of these things, so four pulsars. And early next year they publicized their results and they wrote a nice and this was a huge discovery, and then everybody with a radio telescope started looking for these things, like, wow, oh my gosh, these things are out there. The incredible thing is that once you know to look for them, they're not that hard to find. Pulsars are pretty bright. Radio telescopes were kind of new optical astronomy was dominant at the time, but there were a lot of radio telescopes out there, and by the end of nineteen sixty eight, dozens of these things had been found. And it was another scientist, a guy named Thomas Gold, that put the story together, who said, Ah, these pulsars are the rotating neutron stars that we've been thinking about. What these folks have seen out there in the universe is exactly what we thought might happen in some circumstances at the end of a supernova. So that was a really incredible moment to say, like, Wow, these things, these crazy, weird little blobs that we've predicted might be there as like the tombstone on the end of a supernova, actually are out there and they do this weird thing that lets us find them. I think the discovery that really put a pin in it was the discovery of a pulsar at the heart of the crab Nebula. Crab Nebula is a huge cloud of gas and dust. It's the remnant of an old superd of a star that blew up and spread most of its stuff out there in the universe. So then when we looked with the radio and we saw that at the heart of crab Nebula was a pulsar. We thought, that's what this is, and that completes the story that tells us that at the heart of many nebula there may be these neutron stars. Not all of them become pulsars, but pulsars tell us that the neutron stars are there, that the supernova remnant has this hard little nub at the core of it. But remember that we're using radio waves so far to find these pulsars, and radio waves are not very good at telling the direction of a signal. It's not like an optical telescope, where the photons of very short frequencies nanometers and you can capture them. With a telescope pointed one specific direction, you could tell exactly where on the lens it hit. These things are captured by very large antenna and it's hard to tell what direction they're coming from. So while we say we saw a pulsar in the direction of the crab nebula, it's not like we could really pin down its location exactly. So there's a second part of this discovery story, a part that was caught on audiotape that I want to share with you, But first let's take another break. 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All right, So we are in the late sixties and the field of astronomy was very excited because people had been discovering pulsars. But these pulsars had been seen in the radio frequency, which means they were hard to pin down exactly where they were. People were wondering, are their pulsars out there where? The beams of light that they are shooting are visible light, not just radio noise, but like actual visible beams that our eyes and our telescopes could see. Well, most pulsars, we think are brightest in the radio or the X ray. But the idea was that there might be some optical pulsars. So there were a couple of theorists named John Cook and Mike Disney, and these were not experienced astronomers, but they were curious about whether or not you could see one of these pulsars in the optical So they decided, hey, let's give this thing a shot. Let's sign up for some telescope time, pointed at one of these pulsars and see if we can see any flashes. So these guys not experimentalists, right, they didn't really know how to use a telescope. This is their first time using like real serious astronomical scientific equipment. And they went down to Kidpeak near Tucson and they signed up for a couple of days of observing time. And what they had going for them was that they were going to point this thing at the crab nebula. And they already knew the frequency of the pulsar, so they knew like what freakquency of light flashes to look for. So what they did is they pointed this telescope at the crab nebula and then they looked at the light that came in. But remember that this again was before like dedicated computers where you could rapidly inflexibly analyze your data. What they needed was some sort of like dedicated electronics that could turn their flashes of light into blips that they could study. So there was a guy there who was really good at electronics, and he happened to have exactly what they needed, so they could plug their telescope into this thing and it would analyze the frequency that the time between blips and make a little plot for them on a very small screen, so sort of like a dedicated computer exactly to do this. They happened to stumble across this guy who had exactly this equipment to do what they needed. So they went out there for their first day. They were very excited, thinking, wow, maybe we're going to discover something. And they turned it on and they saw nothing. And what they didn't know at the time was that they had made a mistake in their calculations and they had like tweaked the knobs on this thing wrong, so they shouldn't have seen anything because they were looking at the wrong sort of frequency spectrum. The next two nights that they had were both cloudy, and so they lost all of their observing time and they never would have seen this thing if it hadn't been for somebody else's bad luck. The person with the telescope next after them, his wife got sick, so he decided he was going to stay home and take care of her, and he gave them his telescope time, so they got an extra bonus of a couple of days of observing time that they didn't expect to get. And the clouds cleared and they had a beautiful night, and they set their thing correctly, And they also had a tape recorder running which recorded their conversation as well as the data coming from the telescope. So this little box not only makes a little depiction on their screen that shows from the frequency, it also made a little tick for every blip, So you'll hear those ticks on this tape. You'll also hear them reacting in real time to the discovery they are making.
Hey wow, you don't suppose that.
Can So you hear them saying that it's bang in the middle of the period. Remember that they knew what to look for. They knew the period of this pulse aar, they knew their frequency at which it should flash, so they were looking for a repeated pattern of flashes with just the right period. They had zoomed in on exactly what they were hoping to see. But of course they never knew whether the universe would show it to them, or whether it wouldn't. Here's the rest of their recording.
H it's very true. Yeah, look it is.
So you can hear literally the excitement in their voice. One of them is astonished, look at that bleeding pulse, and the other one is like, I can't believe this is happening right now. It's getting bigger and bigger. You can see them discovering it. You can hear in their voices that they're realizing that they've caught it, that they've seen this pulsar flickering invisible light, that they've pointed this telescope at this weird, far away object and they've caught it doing its thing. So that's a super fun little follow up discovery. They've published that paper, and this must have been a really fun moment for these guys because again, this is the first time they ever went to a telescope. This is the first time they ever looked out into the universe. Most of their science was done with pencil and paper and just sort of thinking about what might be out there. And so I'm glad they got to go out there and actually experienced this moment of discovery. And it also really helped us understand what these pulsars were, because with the optical telescope, with a visible light, you could really pin down exactly where this thing was, and we knew then that it really was at the heart of the crowd nebula and it really was a pulsar. So very exciting discovery and very quickly appreciated, of course by the scientific community. And in nineteen seventy four, just a few years later, Jocelyn Bell's advisor is the first astronomer to ever win the Nobel Prize in physics. That's right, her advisor won the Nobel Prize. Now, of course he was involved, right, You know, a graduate student never works alone. He gave lots of guidance, lots of ideas, probably provided the funding. But it's clear that she's the one who made the discovery. She built that thing, she was out there day to day, she saw it in the data. And there's a lot of discussion these days about why she was left out of it. It's because she was a student. While there are lots of other cases when a student participated in discovery and was included in the Nobel Prize discovery. Holton Taylor, for example, was a graduate student advisor pair that discovered binary pulsars just a couple of decades later, and they were both given the Nobel Prize, even though one of them was a graduate student. Of course, there's the question of whether or not it was sexism. In the history of the Nobel Prizes, very few women have been given the prize and many have been qualified, so it seems like an obvious case of injustice. Burnelle herself is very gracious about it. She recently was given the Breakthrough Prize in Fundamental Physics, which comes with millions of dollars, which she then donated to advancing the cause of having more women in physics. But of course she did note that the journalists didn't ask her science questions. They tended to ask her questions about like how many boyfriends she had. But this kicked off a whole really exciting era of astronomy, because every time you discover something new out there in the universe, it gives you another handle, it gives you a way to learn things, It reveals new things about the universe that you didn't know before. And just a few years after that, we discovered things like millisecond pulsars. These are things that's been around so fast that we see a pulse from them not every second, but every millisecond. So these stars are spinning thousand times faster than the original pulsar spun right every one point six seconds. This incredible, enormous dense object spins around. These things are moving really really fast, spinning like tens of thousands of times per minute. The fastest pulsar we've ever seen we talked about on our episode about the fastest spinning things in the universe is sixteen kilometers in radius and the surface of it is moving at a quarter of the speed of light. That's how fastest thing spinning. I won't tell you the name because it's a ridiculous series of letters and numbers, but it's spinning at seven hundred and sixteen hertz. That means every second, this entire mountain sized blob of nuclear matter spins seven hundred times around, and it's eighteen thousand light years from Earth in the constellation Sagittarius and is sending us pulses very very regularly. The other amazing thing about these pulsars is that they are precisely timed. It's not just like roughly seven hundred and sixteen herts. It's like exactly and every second it's the same. These things do not change, and it's astounding when you see something in nature that is so regular. These things have the regularity the consistency that rivals that of atomic clocks. You can use them as a probe of the rest of the universe because they send out these very very regular pulses. For example, a pulsar was actually the first way that we had evidence of a planet around another star, because when a pulsar has a planet around it, that planet is tugging on it gravitationally as it orbits, and it means the pulsar moves towards us sometimes and away from us other times, and this velocity changes the frequency of the pulsar by a very small amount. But because the pulsars are so precise and so accurate, we can detect that, and if it's a regular shift in the frequency of the pulsar, you can deduce the presence of a planet around the pulsar. How do you have a planet around a pulsar. It's crazy, right, because a pulsar comes from when the Sun was destroyed, so probably some chunk of that nebula has now reformed some planet which is orbiting the pulsar, or some planet happened to amazingly survive the supernova explosion that created the pulsar. And you can also use them to navigate around the galaxy. Because every pulsar is different, each one has like its own unique fingerprint. You can tell which one you are listening to, and you can also tell where you are in its cycle. Is it pointing towards me or away from me? And if you look at multiple of these things, you can tell like how many cycles you are away from multiple pulsars, lets you triangulate exactly where you are in the galaxy. But a whole fun podcast episode about navigating deep space using pulsars, and people have crazy plans for how to use pulsars. For example, they want to use them as gravitational wave detectors. Remember that we have seen ripples in the fabric of space by seeing how these gravitational waves stretch and shrink the distances here on Earth. Well, there might be really massive ones that we can measure they're stretching and shrinking the entire galaxy, and those would affect the pulses from these pulsars, and so a bunch of really precise clocks sending us dings from all around the galaxy can be used to detect gravitational waves. So there's a bright future for the signs of pulsars, as well as a fascinating story that tells us exactly how they were discovered. So thanks for coming along with me on this ride of historical exploration to understand how we actually make these breakthroughs, how people actually win Nobel prizes or are sometimes cut out of it by their advisor, but how scientific knowledge is very slowly, very painstakingly, but very excitingly accumulated. Thanks for joining us. Tune in next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.
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When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is us dairy tackling greenhouse gases? Any farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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