SPEAKER: This is a production of Cornell University.
JAMES LLOYD: I'm very pleased to introduce the visiting AD White Professor at Large, Shri Kulkarni. I should probably introduce myself, because not all of you may know me. I'm James Lloyd from the Department of Astronomy.
So I actually didn't know a lot about the AD White program until quite recently, and I thought I would look up exactly what this program was all about. And apparently, President White, when the university was first founded, expressed concern that Cornell's first faculty, remote from great cities and centers of thought and action, might lose connection with the world at large save through books, [INAUDIBLE] and become provincial in spirit.
And to help ensure this would not happen, he proposed the establishment of a system of nonresident professors, selected for their distinguished achievements in diverse disciplines and walks of life who would visit the university periodically over extended periods of time. And under this system, the resident professors would be thrown into close relations at once with the special professors, and their views would be enlarged, their efforts stimulated, their whole life quickened. And so this is the purpose of the AD White program.
And our visiting AD White Professor Shri Kulkarni, is indeed a very distinguished professor with many achievements. I'll give a couple of quick highlights. He is currently the John D and Catherine T MacArthur Professor of Astronomy and Planetary Science at the California Institute of Technology. His research interests are in compact objects, neutron stars, millisecond pulsars, gamma ray bursts, and the search for extrasolar planets. He received his first degree in physics from the Indian Institute of Technology, and his PhD in radio astronomy from UC Berkeley.
Then he moved to Caltech as a Millican Fellow, and has been on the faculty since 1987. He's a fellow of the National Academy of Sciences, has been a Jansky lecturer, a Fellow of the Royal Society, a Fellow at the American Academy of Arts and Sciences. He's received the Alan T. Waterman award of the National Science Foundation, the Helen Warner Prize of the American Astronomical Society, the Packard Fellowship, and the [INAUDIBLE] Award, amongst others.
And Shri gave a lecture to my introductory astronomy class, Astronomy 101, on Monday, and I realized that most of the undergraduates in this class would not know what most of these awards were. And so I told them that the way to understand exactly how famous Shri is is that Shri is so famous, he is known by his first name alone. So he is as famous as Madonna, at least in the world of astronomy.
And without further ado, I'd like to introduce Shri and turn over the podium to him so that you might have your views enlarged, your efforts stimulated, and your whole life quickened.
SHRI KULKARNI: Thanks. Sorry about the startup. I have no idea. We had three Macintoshes and several combination of dongles and I think we hit upon the right one. The isolation of Cornell. It may happen if US Air goes out of business. And since there's no trains anymore, it may happen within this year, Jamie. OK, so you should make use of me as much as you can. But the part that I was little struck by, had not appreciated [INAUDIBLE] is why all professors thrown at once at this one person. That seemed a bit unfair.
I'll tell you a little bit about progress in cosmic explosions, which sounds like a rather esoteric topic. But as a famous astronomer here once remarked, Carl Sagan, we're all the children of stardust. And explosions are why you're here. So you all should appreciate stars explode, otherwise we'd have a universe full of hydrogen, helium, lithium, and that's about it.
So here's what astronomers think of a complete history of the universe. You start off with hydrogen, some matter, mainly hydrogen helium. And what's shown is redshift at the top right. And this matter has some energy thrown in there. Cell gravity plays a big role. Matter gets clumped and soon gets clumped on a variety of scales and stars are formed. And as these stars undergo nuclear fusion in the center, they explode, most of them in early on. And it is the remnants of this explosion which gives rise to elements beyond lithium.
Occasionally I make a joke too. I don't necessarily sort of do it thinking of someone in particular. But in my department, I say, well, thank god for some of us here that nature produce some lithium. Lithium, it's a very fragile thing. So it can only destroy. Stars don't make lithium. And I can assure you, some of my colleagues would be hard pressed without this conspiracy of nature.
So what you saw was how this matter, which is not uniformly distributed, then goes into this dramatic growth where almost uniformly distributed then becomes clumps, which in this case, are the galaxies. So let me show you another version of this, which is a higher resolution. Might be that. Oops. Since we had to do a lot of this transfer, it might be this movie got lost. So let me see if I can play this again.
Well, I'm afraid I have to show that movie only once. So what you saw there was a formation all the way from [INAUDIBLE] to now. And there are explosions all the time in the universe. Just to give you a sense, roughly once is a second star that dies somewhere in the universe. Explosion, explosion, explosion.
So I'd like to tell you a little bit about some of these explosions. Most of these are ordinary supernovae. And that's been sort of the mainstay of astronomy for almost now a century. And these explosions then produce these complicated or heavier elements. We get earth. And as I remarked in Jamie's class, planets are really the dregs of star formation. When you form stars, you get a little bit of stuff leftover and it's sort of the placental material, a little bit condensed, so you get planets. It's not exactly quality real estate we are supposed to be living on. This is literally the dregs.
So I thought maybe I should give you some background. So I think there are a few things I want you to know. One is any large object, if it is sufficiently large, will collapse under its own weight. You could maybe think of some of your colleagues and have that in mind. No, it's not that. You have to be really large.
So the question is, if the sun is so much mass, why isn't it collapsing? Well, it's not collapsing because there's something to prevent the collapse, namely a pressure gradient. There's higher pressure in the center compared to the surface. So the inward gravitational attraction is compensated by something which is pushing it out. Exactly, precisely, that's why the sun is stable for a very long time, almost about 8 billion years. The sun is in precise equilibrium.
What provides this endless gradient I was talking about? Why in the case of sun we have high pressure due to nuclear fusion in the center? Well, that right away tells you why stars die. Because after a while, the fusion, the material for fusion, namely hydrogen, you run out of that, and then the star has to start its collapse. We now know that these stars, once the fuel hydrogen is exhausted, these stars now become one of three kinds.
A white dwarf, which is the fate of our sun. It's mass of the sun, but radius of earth. It's the fate of many stars, especially in this generation of stars. A neutron star. These are similar mass except they're made of neutrons. Much, much smaller radius. Only 10 kilometers in size. And ultimately, black holes, if in fact the remaining core has got a mass which is more than two times the mass of sun. These are the compact objects, the remnants leftover after the stars die.
Now to understand the explosion part, you ought to know there's gravitational binding energy, which sounds very fancy. I have this object here and I drop it. And there's obviously energy that's gained just falling through this. And that sort of gravitational binding energy. Which means if I want to take earth apart, I have to actually do some work, because everything is sticking to each other because of gravitational force.
So this binding energy is inversely proportional to the size of the source of the star. And that's why I was particular in giving you the sizes of these stellar remnants. A white dwarf heads the size of earth, neutron star the size of Ithaca, [INAUDIBLE], and a black hole is only a few kilometers in that sense, in their effective size. So their very production leads to a large amount of energy.
And conversely, just like this example I gave you, when I do drop and it hits, it goes down into the gravitational potential, you gain energy. And in the same way, when material forms onto these objects, you also gain energy. So you gain energy twice. One when you form it, because you've got starting from a large star and becoming a small star, and the other one is as you keep dumping matter, which is called accretion power. In fact, the realization that accretion power is in fact the dominant source of energy in the universe took place here by [INAUDIBLE] in the early '60s.
So after these explosions, you get supernovae. And here we can see that there's a [INAUDIBLE] remnant, 400 years old now. And actually, if you take a Chandra image, you can see it's a cosmic advertisement. There's a lot of calcium you actually see. The words aren't there. I'm pretty sure no one got fooled by that. But that is actually calcium you see. So when these sorts of stars die, they produce things like calcium. But other kinds of stars when they die, they produce iron. And that's terribly important for us, because it's only when we start producing those you go beyond that group of elements.
So that's sort of a broad history. So to summarize, universe starts off hydrogen helium energy. And because it's not absolutely homogeneously distributed, you get this gradual growth of structures. So it's sort of a curious thing. If the universe were formed perfectly symmetrically, that is the density here is the same as density there, the universe would be, just nothing would happen in this universe. It would just expand. So it's a curious thing. Most of the interesting things in the universe are due to slight asymmetries. Anyway, I'll leave you with some sort of zen like thinking that you may want to do about that.
Then we get these explosions. The explosions generate elements that may make up a large part of our constitution. And unless these explode, unless these stars can go and see the interstellar medium, it's not very useful. If a star just, all the material [INAUDIBLE] or just goes into the remnant star, the composition of the universe doesn't change. But all these things do happen.
So let me start with sort of the big change that has happened in the last 40 years or something. And the first one I'd like to talk about is gamma ray bursts, because these are the most exotic explosions. So while there's one supernova every second that's happening somewhere in the universe, probably there's our guess is there's probably one every 1,000 seconds of gamma ray bursts. Maybe one every 10,000 seconds. And just to give you an idea, a day has 10 to the 5 seconds, 100,000. So gamma ray bursts are rare, but they're very dramatic.
So these were discovered actually in the mid '60s because the US and then USSR signed a treaty called the Outer Space Treaty which prohibited testing of nuclear devices above ground. If you have a nuclear explosion, you will produce hard x-rays.
In order to verify that there won't be tests in space as opposed to just, say, certain atmospheric tests, the two countries built the satellites which carried these hard x-ray detectors to in fact to make sure that there's compliance that there are no nuclear tests carried out in outer space. By the way, this Outer Space Treaty was the first time which actually lays down on ownership of asteroid material and so on and so forth. It's a curious document actually worth revisiting.
So what these people found, what the people who built this found, is in fact, they did find hard x-ray bursts or gamma ray bursts. And it turned out to be not of terrestrial origin. It's fairly easy to prove that. And so just imagine this is earth and there's this satellite circling around. Now let's say there's a gamma ray burst in that direction.
Now, there was a constellation of satellites. So if there's a satellite on this side of earth and another one on that side, it's pretty clear if a burst is coming from that direction that the gamma ray burst reaches this satellite first on my right side, and then it reaches the other one a little later, because light takes a certain time to travel, which is tens of milliseconds in this case, which is good enough to do triangulation and show that this was of extraterrestrial origin.
So this was towards the end of '60s that the results were announced. And the origin of these objects is very, very mysterious, or was very mysterious for almost 30 years. So much so that a major satellite, one of its main purposes was in fact to understand the origin of gamma ray bursts. So here's the Compton Gamma Ray Observatory being launched in the early '90s.
This is a very large spacecraft. It's the largest civilian spacecraft to be launched. And you can see this from the shuttle bay. And this is the size of a school bus, just to give you a sense of how big this is. And it carried a number of experiments. And one of it was to study gamma ray bursts.
So what astronomers found, until then it was known, but this mission really showed very well is, gamma ray bursts are in fact isotropic. So what does the word isotropic here mean? It's that the chance of seeing a gamma ray burst is the same in this direction or in that direction or any other direction.
And the rate as seen by this experiment called [INAUDIBLE] was a few a day, one a day or so. So once a day there's a blinding flash of gamma ray bursts. And it's random in the sky, random time, random location. And this is shown in a particular coordinate system in which the stars would lie along the equator. This is called a galactic coordinate system.
The center of the galaxy would lie here. And if I showed you the optical picture, which it will be on the next view graph, you'd find more sort of stars that will be here. So if gamma ray bursts came from ordinary stars, then you expect they too would be lined up along the equator as other stars are. Instead you can find it's perfectly distributed on the sky.
So here's an artist's sketch of what our galaxy would look if you went outside the galaxy and looked at it sideways. Here's the center of the galaxy. The galaxy is primarily a disk of stars, a very thin disk, with some old stars in a sort of spherical distribution. And the sun is located out here. Not particularly a special place. We are not in the center of the galaxy. We're not way out of the galaxy. We're sort of somewhere in between.
And you can see that if gamma ray bursts were distributed like the stars, then the distribution of the sky cannot be isotropic. In fact, it's very easy. You go out, especially in the northern hemisphere, you go out in summer time, you see a band of stars, the Milky Way. And that's simply looking towards into the galactic equator. In the southern sky, it's more spectacular.
So we have these very mysterious sources that are a few times a day, they're very bright. If you could see these bursts with your eyes, which we don't, and towards the end if I have some time, I'll explain how fortunate is it that we don't see gamma ray bursts at Earth. And their origin is random, anywhere in the sky. So you need a model for this. Obviously not stars.
So obviously, you need something. Which one idea is we know it is not stars, because there are more stars in this part of the sky compared to that. So what if I hypothesize that there's a very big sphere around us, a corona a crown, in which there is mysterious objects lurking around.
And then they burst, and because it's so big, this sphere, compared with my offset from the center of this galaxy, I will notice the statistics will be such that I'll say, ah, it's more or less isotropic. Well, it's possible. Except it's very mysterious. This artist's sketch shows. It tries to show you all the things we know. Mostly in the disk, a few things so called halo, and there are nothing here. So then you have to come up.
So in the mid '90s, it's slightly better to divert physics for a long time, since I would say maybe late '60s has been a very boring field. Nothing much happens in that field. So a lot of those guys read astronomy papers. And they wrote many articles. Well, maybe there's some weird cosmic strings colliding with each other, phase transitions, whatever. All wrong. All wrong. But that didn't make sense, even with a minute of reading.
The other big sphere, there's one other big sphere here, which I haven't plotted. And that is the universe. We now know that there are as many galaxies in any direction as any other. And this is in fact the basis, this is the ultimate Copernican revolution that we have no preferred status in the universe at all. Well, the problem here is that if you put gamma ray bursts in the universe on the larger sphere we know of, which is the entire universe, then I'm still receiving this blinding flash here at earth, but now I'm going to make the distance very far away, across the universe.
And then you know the famous candle inverse square law experiment I'm pretty sure we all did in third grade, or fourth, I forget. You take the candle, you measure how much flux there is, and then you go further away, the flux decreases. And so it decreases as 1 over distance square. So if I have the same, I have flux, and I want to say, how much was that candle?
I have to multiply by distance square. It will make the distance as large as the size of the universe. This is an astounding number. How astounding it is? Well, it it'll be something in astronomy units 10 to the 54 ergs per second. Makes no sense at all because it's one followed by 54 0's. But let me put it another way. If you take the entire mass of sun, the solar mass of sun, and you find another anti sun, anti-matter stuff, and put them together, E equals Mc squared stuff comes out, energy comes out. That's what happens in one second. The total annihilation of a solar mass of material in one second. That is an impressive thing.
Now, most astronomers, we are used to very large numbers. It's 10 to the 54. It's no big deal. We can really handle very large numbers. Unfortunately, the only large number we don't handle is our paychecks, which tend to be more modest. This is a very tough crowd. OK, I'll try harder. This is a large number for astronomers. This is very challenging. Bashing off a whole sun in a second, no one knows how to do that, really.
So that is a problem. So much so that astronomers had a meeting in Washington. I went to that. You can see April 22, 1995. It was a room like this, except there were two big aisles, and a somewhat smaller central aisle, if I remember right. And you wore a button. One that says, gamma rays are galactic, which means they belong to this mysterious population of in the corona. Or they're cosmologic, which means they're somewhere out there in the cosmos. And if you really didn't know which one, you wore the button other.
I'm always a very practical guy. Collected them all. I didn't have a particular basis. Because it's always good, if you want to trade, you should always complete sets. Everyone understands this. So anyway, these are collector items. If you're interested, we can negotiate after the talk. I have them.
And let me get the punchline away of where this talk is going. The answer is all these three buttons are right. In 1995, which is a little bit over a decade ago, we thought there was only one button which was right. And it turns out 13 years later, all buttons are right. That's the beauty of astronomy, that the universe is actually much more imaginative than astronomers can be.
So in the next 10 slides or so, I'll tell you what caused this modest revolution in what is considered a first class mystery in astronomy for nearly four decades. So the revolution came about unexpectedly, actually, with the launch of an Italian Dutch satellite called BeppoSAX. Occhialini, [INAUDIBLE] whose nickname was Beppo, an Italian physicist who almost missed discovering the anti-electron, actually. He's well known in more technical circles for inventing what is called as a coincidence, what we now consider as both coincidence and anti coincident techniques, which sound obvious, but it wasn't so obvious till his invention.
Anyway, so the Italian Dutch satellite carried an x-ray imager and a gamma ray detector. So this x-ray had two x-ray measures. So basically, the problem with gamma rays is that at such high energies, the energies of these gamma rays we are talking about is about, oh, 100 to 1,000 times larger than the energy of the x-ray you get when you go to your dentist.
X-rays can be made. You can make reflector optics with x-rays. But gamma rays are so energetic and so small, effectively, it's hard to make reflect to optics. So you can't make images at gamma ray wavelengths. So that's why you couldn't figure out. You know roughly where it is. But in order to really figure out how to make images with high precision with very high resolution, and that is not possible.
Anyway, so this satellite, they were able to find, in fact, a gamma ray burst goes off, then use x-ray as a different technique, find likely fading counterparts, use another telescope, and then find a localization. And once you had that, the game really became very interesting. So that's called the afterglow. Afterglow phenomena is the burst goes off and then you get low energy radiation, x-ray optical radio, for many days, which allows you to then go and conduct studies.
So one of the things that we did early on was this gamma ray burst 970508. The gamma ray bursts are known by their birth dates. So 970508 means 1997 5th of May. I always remember this burst extremely well because we wrote lots of papers. And my wife sort of minds this because it's also her birthday. And it's pretty clear, many Freudian slips have occurred, which goes to show which one I remember first. But honest is the best policy.
So here's a view of Mauna Kea, which is the tallest mountain in the Pacific in Hawaii, the big island of Hawaii. And you can see the Pacific Ocean. And right here on the top, there's almost a billion worth of astronomy capital invested in these telescopes. And these are telescopes that we jointly operate with the University of California system to get telescopes. And we are able to show by looking at the optical afterglow that this gamma ray burst really came across the universe. So it is a challenge of how a star can convert generate so much power in such a short time.
Well, having established that, for the next few years, life was easy. We were writing a paper almost every two weeks. This is the part I like in astronomy. It's not a hard field, actually. If you're reasonably bright and if you have a reasonable amount of imagination, you can write papers. In other fields, people have to struggle. I mean, I went to a talk in physics. It's terrible. There's this apparently sand pile and the person is trying to compute the angle of the sand pile. I thought, oh well, OK. OK, sorry.
So we start studying this at radio wavelengths. And this is a nice thing about doing astronomy. You can buzz around today Australia, tomorrow Puerto Rico, day after Switzerland, who knows? So anyway, we have telescopes here in the US, in Australia, New Mexico, California. And it's called Very long Baseline Array. You gang up these telescopes and you make very fine images. So in fact, we were able to make an image of this gamma ray burst.
And in fact, we observed it over here and we found it expands faster than speed of light. Now, I know that some of you guys may mistakenly think, gee, isn't that why Einstein got his Nobel Prize? Should we not withdraw that? Well, two things. No, he didn't get the Nobel Prize for saying speed of light is something you can't exceed. And this really didn't exceed speed of light.
It's a geometrical trick and it's called superluminal expansion. It's been seen in other places. So in a rather short time, many astronomers plus our work, we were able to in fact establish the energy scale of this gamma ray burst. And in fact, later I will show the depth of massive stars.
This is a bit of an in joke, the next one, so I have to prep you. I didn't grow up in the US. I came in as 21. So some phrases I don't instinctively don't understand. But I'd read this comic strip and I said, yeah, there's something that makes sense here. So this guy, and that's radio source 3. Oops.
That's radio source 3C390.3 and that's radio source 3C231 and over there. It says, why radio astronomers often strike out. Of course, it's a boy and a girl. I understand. I quickly learned. So I only went to optical observatories when I had such other intentions in mind.
So a little later, most of the stuff I've been doing in our department, most of my colleagues, they're very interested in more distant. It's sort of like each community has their sexy, in thing. So the in thing in astronomy for many astronomers are cosmology, very distant things, face of god, and all that sort of stuff.
But I'm a bit too young to be senile and be interested in cosmology. But I knew with this discovery that we made something big, because as soon as we found this burst and we showed the redshift was 3.4, my colleagues started trooping into my office. So what was a novelty then became something of interest.
Same thing. Burst goes off. We run around, use Palomar, [INAUDIBLE], rush around, use Hubble, and find [INAUDIBLE] coincide. So the galaxy, use Keck, get a spectrum. And we showed this is a redshift of 3.4. And this got a lot of attention because it turns out if you want to view this as an extreme phenomena, here's a timeline for the universe.
And there are several ways. You can say, what is the temperature of the universe? Basically it's the energy density. How hot was the universe? We all know the universe today is 3 Kelvin warm. And in the past, it was hotter, because it was more compact.
So if you go back in time, it'll be hard enough. You're looking at very high temperatures. Here's 10 to the 10, 10 to the 15, 10 to the 20, 25, 30 Kelvin. And here's a time scale [INAUDIBLE]. 10 to the 18 seconds, 10 to the minus 42 seconds. It's an impressive range of phenomena in physics that astronomers explore.
So the gamma ray bursts roughly occupied this region, which is what the universe was within the border few microsecond after birth. So a friend of mine, a colleague, suggested we call it as big bang two, which I thought was a bit of a cheat, because the big bang is an explosion that occurs at all points at the same time. And this is a point explosion.
But nonetheless, being practical, I saw this is a great thing. And indeed it was. It got reportable like 300 newspapers. And the part I liked the most was it says, Indian detects big bang two. I like this one. And this was right after the Indians had undergone explored the nuclear devices which only added to my sense of humor about these things.
But we know we really made it big when here's a German newspaper. And somebody [INAUDIBLE] extreme phenomenon and so on. And here is Bo Derek. Shall we say she's scantily clad? And I don't want to be hauled off to a PC tribunal, so it's suitably over exposed.
And there's something about sexual motive murder. This is like the Pope's guard killed someone same day. So I thought, well, this is mainstream. Bo Derek, murder. Here we are, gamma ray bursts. So this is the best a scientist can hope. Now gamma ray burst is very much part of our lexicon. Everyone understands what this is.
Let's try to now go into and see what is this. How do you get such large energy, the energy, the power? And here the idea is that there is some black hole involved. Remember I told you in the third slide that the creation power that is when you drop material into a compact object, you also release the energy. And the more compact it is, the more you release, because it is a small size.
What is the most compact object we know? Black hole. In that sense, what is even more compact than a black hole? A rotating black hole. So if you take an ordinary black hole, like a solar mass, its size is one kilometer, you rotate it 1/6 of a kilometer. You get even six times more energy. In fact, the black hole, which is maximally rotating, can convert about half, 50%. That is, if you drop a gram, then 1/2 gram percent times c squared is the energy released. So black holes, rotating black holes are immense energy power generators.
So how do you make rotating black holes? There are two ideas. You have these two neutron stars. We now know that work done by Professor Taylor at Princeton, the two neutron stars, they go around each other, they generate rotational waves. It's a prediction of Einstein's theory relativity, a general theory. And it's been verified through actual pulsar observations. At some point, since this system is generating waves, it'll coalesce, form a rapidly rotating black hole, and then through processes we don't fully understand, you get a gamma ray burst.
The other one is you start off with a large star, a much larger star, and it's got a small amount of rotation. But remember the famous experiment. I'm sure all of us maybe in fifth grade at this point, it's easily done in Ithaca almost 300 days a year you can do this experiment. You simply go out, put on your skating shoes, and you're in the parking lot, have to dumbbells, and you spin around, and then withdraw the arms you spin very fast. This is the angular momentum conservation. And so when the star collapses, it becomes a rapidly spinning black hole.
So here's sort of an artist sketch. Here's a massive star. Nuclear fusion in the center, and black hole is formed. Material is now raining on the black hole. Jets of matter come out. And relativistic, that means very close to speed of light. They pierce through the star. And boom, that's where you get the gamma ray burst. And if it is directed towards you, you'll see a very bright thing.
Now, tempting as it may be, I won't do that, because it's actually harmful. But let's look at this laser beam here. If you're looking around the throat of this laser beam, it would be very, very bright. In fact you would be amazed. You'd think if it is really generated by some sort of a heating of a source, it would be very, very hot.
But this is called the collimated beams. So if you're down the throat, you will see a very bright thing, but if you're away from that, you won't see as much. So gamma ray bursts hardly appear to be very bright, because they're like laser beams. You're seeing them down the throat. Which means for every gamma ray burst you see, there are hundreds, perhaps even 1,000, that are not beamed towards you.
There's another group of gamma ray bursts which is very much in vogue right now. They're called short gamma ray bursts, and they come from a different origin. They, in fact, we think, now it's speculation, we think in fact, they come from this coalescence of neutron stars. This is a topic of great interest here at Cornell.
And I typically like to write very short papers. It's very hard for me to write a paper over more than a few days. So I like writing letters rather than any tomes. That's why I'm showing a picture of nature, because my style is such that once I get inspired or whatever, I get up in the morning, write a paper, and the end of it. So you don't really have to pay. It's an excellent way for those of us with ADHD.
So here's a short gamma ray burst. Same thing. It was detected at one satellite. We use the Chandra x-ray satellite, and then we use Hubble Space Telescope. And we're able to show that this gamma birth came in the outskirts of this otherwise anonymous scraggly galaxy. That's a beautiful astronomy. Can you imagine, you sitting in your office and you say, yeah, OK, satellite one, get Hubble, Chandra, use the VLA. It's like, this is fantastic.
Astronomy game, boys with toys, the best toys ever. I mean, my pay may be low, but every time I use Hubble, I'm getting like $1 million of money someone has spent just for one orbit of Hubble. Maybe it's 10 million, I don't know. So this is a great time to be doing astronomy, because you can really execute these sorts of things which are almost even unimaginable 10 years ago.
So here's another toy. What we do is just like this laser beam, except there's a laser beam from Keck we launch. And this will be a yellow beam like sodium lined, like the one you see, the sodium lamps. And we shine it up.
And it so happens that every year, roughly actually around this time, there's a broken up comet which seeds a bit of our atmosphere with sodium, amongst other things. So there's a thin layer of sodium 90 kilometers above. So we shine this light and the light gets reflected by the sodium layer and we form an artificial beacon in the sky 90 kilometers above. And that beacon then serves as to take the atmospheric shimmer.
And now this has become pretty routine. So we did this. And in fact, we were able to show that in another case that the gamma ray burst took place in the outskirts of what is called as a red elliptical galaxy. This is a galaxy which is very different from the previous galaxy I showed. And these indirect clues are all consistent with the idea of this these two neutron stars which are slowly spiraling and then coalesce.
So here's a high quality simulation. And it shows, in fact, it should, but maybe because we loaded this movie, it has not been shown. This is a black hole and there's a neutron star. And what this would have shown in about five seconds, five milliseconds, this would have, in fact, been shredded, and in fact, would reasonably explain the origin of the short hard burst.
But in the process of two stars going around. I also told you that Einstein's theory of general relativity predicts that, in fact, there should be gravitational waves. But if you're emitting radiation, losing energy, it must come at the expense of something, and two stars get closer because they're getting the potential wealth. Well. So you're converting the potential energy into radiation. Which means the best way to study this is in fact to see the gravitational waves that is predicted by this theory directly.
And this is sort of the holy grail of astrophysics at this point. And the National Science Foundation in the US, the Europeans, have spent about $400 million putting two instruments, one is called LIGO, the other is called VIRGO, to in fact detect rotational waves directly, which would be a technical coup and a great achievement.
So here we have LIGO in Australia. They're trying to do something near Perth. So there's a worldwide effort to finally start seeing these sort of gravitational waves. It's an esoteric prediction of GR. And astronomers, again, come to the rescue of physicists, because this is not an experiment you can do in the lab or at home. You really need these very large objects which are spiraling in this death spiral, and that's a source of energy. So the next five 10 years should be interesting from the point of view of exploring extreme gravity through actual observations.
So let me now step back. I've sort of give you a rush of these things where we went from having mysterious gamma ray bursts to actually now coming up and speculating maybe they are the endpoints of certain kinds of stars. They involve very extreme gravity. They may even test some of the finer points of extreme gravity.
However, if you just step back and look at this as an astronomical phenomena, 100 years ago astronomers noticed-- they had been noticing before. But the idea of nova became very common. So 100 years ago, it was quite fashionable to study a star which suddenly brightened up and then disappeared. And that was called a nova stellar, new star. And then it took another 30 years to figure out that what we call as a nova stellar, this transient optical source, in fact is not just one family. In fact, they're nova and supernova.
That is, nova are a different kind of breed altogether than supernova. And in the nova family, now we know there are five kinds of nova, because they involve white dwarf, neutron star, black hole, and the surfaces. And since a black hole doesn't have a surface, there are five and not six types. And the supernova, it turns out, there are at least two major families, a thermonuclear explosion and a core collapse.
So 100 years ago, what astronomers thought was one name turns out to be many different families with sub families and so on. And again, that should give pause. Now, you could, of course, one idea is 100 years ago, people weren't as smart as we are today. Probably not a good assumption. I'm pretty sure they thought that they had found something. So if it turns out if I tell you gamma ray bursts is not just one family, you should not be surprised.
So let's go back 100 years. Let's go back only 30 or 40 years ago. Here's Scientific American, so in the '80s, and this was an article on gamma ray bursts. And a famous astronomer who wrote this, and it was the informed opinion of the masses, that gamma ray bursts were galactic objects. The all involve neutron stars. Here's a neutron star undergoing a star quake, a neutron star being hit by a comet, a neutron star undergoing a magnetic flare.
And the short answer is, we now have found one majority of the gamma ray bursts of extragalactic. We, in fact, have examples of a neutron star undergoing a flare and masquerades as a gamma ray burst. And we have an example of a neutron star or a black hole acreting matter in chunks. I don't know if it's an asteroid, but something else. So in fact, it goes to show that ecological niches here are occupied.
So the next one, hopefully it'll play well. Basically, I thought there's a famous statement by Rumsfeld. And he's actually a deep thinker. You guys may not agree with that, but I thought what he said makes a lot of sense. Let's see if it works. Lloyd, how do I? So let me start again. How do I play this?
- That there are known knowns. There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know.
OK. OK. So of course, the context there was a bit different. He didn't have explosions of the cosmologic or celestial kind in mind. He was talking of weapons of mass destruction. So let's see exactly what he says.
So he says, reports that say something that has not happened is always interesting to me. So if you don't find something, it doesn't mean it exists. The message is that known knowns, there are things we now know that we know. Supernova, nova, that's what I think he was saying. There are known unknowns. That is, there are things we now know that we didn't know. So there are extensions of supernovae and novae. And now gamma ray bursts. We didn't know, we now come to know.
But there are also unknown unknowns. There are things we do not know we don't know, and each year we discover a few more of the unknown unknown. So he's saying things will be found. In fact, it's a deep statement. And it's so deep, I've been to several meetings now and many people like this.
So here's an unknown unknown that got discovered after that. So we found, in fact, a new kind of explosion here in the nearby universe just in the Virgo cluster. And we only know the name. It just says luminous red novae. It is luminous, it is red, and likely a nova. I thought we should come up with a fancy name, but then I found a cartoon, which is about 30 years old now. It says, somewhere probably between a nova and a supernova. It is. This object is brighter than a nova, but fainter than a supernova. Probably a pretty good nova. So I think maybe we should simply have called it the PGN. Well, that was a couple of years ago. But Rumsfeld said, remember, every year we'll find a new unknown unknown.
OK, what about Recently well, now we go to radio astronomy. Radio astronomers have been conducting searches for pulsars, the known knowns. It's a mainstream activity. And somewhere along that, they in fact found a very bright radial pulse. It's a bit hard to explain this, but it's got chirp that it sort of has a whistle like sound. And it's only five milliseconds in width. And we believe this is of extragalactic origin. It's clearly an unknown unknown. The origin of this is highly debated even today.
So the Rumsfeld law for discovery and a new class is true for the last two years. So we assume it is true into the future. I mean, this is reasonable. So decide to take that very seriously and started a program called the Palomar Transient Factory, which will turn out pretty standard stuff every night, but with the goal of finding one new unknown unknown per year. And this is the concept here is we'll survey the sky, we'll analyze data in real time, and when we find a transient, we'll study them and we'll make progress within the same night.
Radio astronomy is also poised to do similar things. Here's the Allen telescope array in Hat Creek in northern California, managed by UC Berkeley. And they're using novel technologies and ideas to make large images of the sky and find transients. And in the future, the goal is to do something called a square kilometer ray and to find new radio transients. I think I'm very optimistic. This will be a very exciting field.
There's a law called Moore's law. Moore's law tells you that in semiconductor industry, things double every 18 months. That is, your performance. That is, if you pay the same amount every 18 months, you get better performance by a factor of two. Sometimes there's another law or observation called Kurzweil's law of accelerating returns. I'm not necessarily sure that I believe that.
But you can come up with a new law of synergies, actually, which is if you just had Moore's law, think of just having Moore's law, where only disk capacity increased every 18 months. It won't be so fun. You'll just store more and more pictures. That's all it will do. But if disk capacity increases every 18 months and computing increases every 18 months, then you can do more interesting things, like Google's patent recognition immediately recognizing three gigabytes of data how you want to see who's who. You get really more multiplicative effect when four or five things have similar capabilities. And I think that's what's happening in astronomy.
What we are really now seeing is due to this large progress outside astronomy, we are getting the synergy of larger computing, very cheap sensors, bandwidth, and then ability to respond instantly because of connectivity. And that's why I think this is a very interesting field. This couldn't have been done 10 years ago for that reason, because one or more would have been missing 10 years ago. So I predict you will end up seeing lots of interesting things.
Now, a talk like this can be sometimes educational, but it's not guaranteed to be so. So I did want to leave you with something of value. I probably spend an hour plus an addition of 10 minutes due to our lack of connectivity here. And so let me go back and leave you with something really interesting and of great value to you. I assure you, you may forget everything I've told you 10 years from now, but this one, the next thing I'll tell you, you will remember. OK, are you ready for that?
Remember I told you that is one of the stellar remnants of neutron stars. Now, a particular kind of neutron star called as pulsars. So here's an example of a pulsar. Here's a supernova remnant. That means a star exploded. In the center is this neutron star. And this neutron star is slightly special.
That is, the neutron stars which they're highly magnetized and they're rotating and they produce pulses of radiation. That's why pulsating radio stars or a pulsar. So in this case, there's the pulsar, and it has an axis here. If you wish the north and south geomagnetic or a neutrino magnetic axis.
So I won't do that. But you can imagine me having a light beam, which is my magnetic pole, and I shine this light on you, then I go around, and then I come back, you'll see a pulse like a rotating lighthouse. That's what pulsar sees. You see a pulse. And the study of pulsars, mainstream activity right here at Cornell. Arecibo Observatory is most famous for that.
So what is a thing of value is that the Australians have been really big pioneers in this field. Australia has a similar complex. They've got their field, they're far away, they're very isolated, and so on. And actually some of these [INAUDIBLE] observations survived. I think because it's so isolated in my opinion, every time I go to Australia, it's my feeling these guys are nice, but a little bit on the naive side, I would say. And that's a part of the thing that you have to remember.
So you land in Australia, Sydney, Melbourne, maybe even Perth. And get off the plane, go and accost an Australian. They're usually nice people. They'll always be very friendly. And you say, look, I attend this talk by this guy, and I want to show something, but I need a $50 bill. So you get a $50 bill from this Australian person. And there's a $50 bill. You should say look, here's the Parkes radio telescope, the biggest radio telescope in the southern hemisphere. It was a marvel by the time it was constructed. A pioneer in many, many things, including getting the signal from the moon.
Have many of you have seen the movie The Dish? Boy, Cornell is a very serious place. It's hard to believe that the only people who've seen are the faculty. Anyway, it's a nice movie. It's sort of a two beer movie. You drink two beers, the movie is over.
And then, you say, well, and it's done a lot of pulsar research. And you can see, these are pulsar traces. This is actual real data. These are the pulsar traces. And they actually go up and down and so on and so forth. And the idea is that by this time, you learned so much from a lecture, you will actually be able to enthrall them with pulsars, gamma ray bursts, the works, black holes, whatever. And then you utilize the fact that they're naive people, slowly pocket the $50, and walk away. On that practical note, [? end ?] [? of ?] talk.
AUDIENCE: I have a naive question, which I'm allowed to ask because I'm an Australian. Are these gamma ray bursts a burst at the source, or is it bursty because of a rotating whatever? And if so, why don't we see them repeat it, as we do with pulsars?
SHRI KULKARNI: No, we don't believe they're rotating. The whole phenomena is in a very short time.
AUDIENCE: At the source?
SHRI KULKARNI: It's a cataclysmic explosion. That's it. Now, there are a small fraction of these so called soft gamma repeaters that do masquerade as gamma ray bursts, as short gamma ray bursts, which some study you can figure it out. And they do repeat. These sort of massive bursts, they have maybe once in every 30 years or so. But we know, because we've seen them.
AUDIENCE: Can you take a, just by looking at the burst of gamma rays, can you tell what the source of them were? Do you always need secondary observations.
SHRI KULKARNI: No. The question is, can you just say by looking at the flux on the duration of the gamma ray bursts anything of the origin, it turns out no, not at all. The technical term is so-called luminosity function. That is, you took gamma ray bursts. If you could measure the luminosity at the source itself, how standard they are. Do they have the same wattage? The answer is no? They have wattage that is incredibly diverse.
AUDIENCE: The neutron star lighthouse effect that you were talking about, that doesn't point exactly at the earth, right? So how exactly are we see these photons if they're pointing some other direction.
SHRI KULKARNI: Only the ones which are beamed. It's called beamed. Only the ones whose geometry is favorable to you. So for every one, there are many you don't. So literally gamma ray bursts, these opening angles for gamma are even more extreme than pulsars. Some of the opening angles for gamma ray bursts are literally that small size. So if you see one, you're very lucky unless there's a huge conspiracy.
Then the one which has pointed that way, you will name a C. So you should say, what is a fraction? Assuming they all happen isotropically. And the answer may be, as I said, in some cases, it may be as large as 1,000. So every one you see there are 999 you don't see. So you have to multiply what you see by things you don't see.
AUDIENCE: So when you were saying earlier that gamma rays were just looking at the map and seeing isotropic that they're coming everywhere, but yet there are still sources of gamma rays that come within our galaxy? Are they just so infrequent that they don't alter the statistics at all, you don't see them on the line of sight of our galaxy?
SHRI KULKARNI: So the question is, what is the rate of occurrence of gamma ray bursts in our galaxy? It's actually hard to know what happens locally. We have a much better sense of the rate further away. But it's roughly about likely, not less than 100,000 years. So once every 100,000 years. Maybe as high as once every 10 million years. There are far more gamma ray bursts when the galaxy is younger. You know that. So it's a bit hard to know what it is in some sense as our galaxy has aged. Gamma ray bursts go with young stars, more than with older stars.
And I did tell you something. It's good we don't see these gamma ray bursts directly at sea level. So let me tell you why that's interesting. The reason is that if you do have a gamma ray burst in our galaxy and we are so fortunate or misfortune to have it nicely lined up to receive the brunt of this radiation, one of the reasons here to go about Earth's atmosphere is gamma rays don't reach sea level because we have an atmosphere.
And the reason is that these gamma rays, they are so energetic photons, they can cleave the bonds like oxygen, oxygen is bound. So that it can actually cleave and make free oxygen it can also cleave nitrogen, which is bone molecule, into free nitrogen and so on. And because it takes energy to cleave these bonds, so by the time it reaches the sea level, it's all dissipated. Which is why we have to actually go up in space to study gamma rays. But if you do have a bright gamma ray burst in our galaxy, then something terrible happens and maybe not so terrible.
And that as a gamma ray bursts progresses and hits the Earth's atmosphere, it will start clearing all these bones. And you get free nitrogen, free oxygen, and so on. And very quickly, nitrous oxide is formed so. So right after the gamma ray burst happens, . there will be a lot of nitrous oxide And most of us will die laughing, which is I think the best choice we have.
I gotta tell you there are few people I know, especially in our department who went for this will have no effect. So if you want a wish if, I don't know whether it be religious or not. But if you had to take a multiple choice, you had to choose one, death by whatever. Cost me. Asteroid, hitting asteroids, terrible stuff. Don't go for that it's really bad. And I would simply go for gamma ray bursts.
We've received your request
You will be notified by email when the transcript and captions are available. The process may take up to 5 business days. Please contact firstname.lastname@example.org if you have any questions about this request.
Cosmic explosions play a critical role in our lives. Stated simply, without cosmic explosions we would not be here. Shri Kulkarni, A.D. White Professor-at-Large, Director of Caltech Optical Observatories and Professor of Astronomy reviewed the development of the history of cosmic explosions (a subject which is only a hundred years old) and ended with the great progress achieved in the field. Gamma-ray bursts, magnetars and supernovae have now entered the lay language.