Category: Podcasts

As a tribute to John Mather and George Smoot, the two leaders of the Cosmic Microwave Background Explorer (COBE) satellite science team, and winners of this year’s Nobel Prize for Physics, we head back to the beginning of everything – the Big Bang. Follow as we trace the Big Bang’s discovery, and one of the most important lines of evidence: the cosmic microwave background radiation which was predicted by theory and then discovered by accident.
Continue reading “Podcast: The Big Bang and Cosmic Microwave Background”

Dark matter . . . What is it? Nobody knows for sure, but it’s definitely there. Or maybe it’s not there, and we just need some redefinition of gravity at vast scales. Join Fraser and Pamela as we discuss the discovery, detection, and possible explanations of dark matter.
Continue reading “Podcast: The Search for Dark Matter”

You have lived on the Earth all your life, so you’d think you know plenty about planets. As usual though, the Universe is stranger than we assume, and the planets orbiting other stars defy our expectations. Gigantic super-Jupiters whirling around their parent stars every couple of days; fluffy planets with the density of cork; and Earth-sized fragments of exploded stars circling pulsars. Join us as we round up the latest batch of bizarro worlds.
Continue reading “Podcast: Hot Jupiters and Pulsar Planets”

Arial photograph of LIGO. Image credit: LIGO. Click to enlarge.
In the past, astronomers could only see the sky in visible light, using their eyes as receptors. New technologies extended their vision into different spectra: infrared, ultraviolet, radio waves, x-rays and gamma rays. But what if you had gravity eyes? Einstein predicted that the most extreme objects and events in the Universe should generate gravity waves, and distort space around them. A new experiment called Laser Interferometer Gravitational Wave Observatory (or LIGO) could make the first detection of these gravity waves.

Listen to the interview: Seeing with Gravity Eyes (7.9 MB)

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Fraser Cain: All right, so what is a gravity wave?

Dr. Sam Waldman: So a gravity wave can be explained if you remember that mass distorts spacetime. So if you remember the analogy of a sheet pulled taut with a bowling ball tossed into the middle of the sheet, bending the sheet; where the bowling ball is a mass and the sheet represents spacetime. If you move that bowling ball back and forth very rapidly, you’ll make ripples in the sheet. The same thing is true for masses in our Universe. If you move a star back and forth very rapidly, you will make ripples in spacetime. And those ripples in spacetime are observable. We call them gravity waves.

Fraser: Now if I’m walking around the room, is that going to cause gravity waves?

Dr. Waldman: Well it will. As far as we know, gravity works at all scales and for all masses, but spacetime is very stiff. So something like my 200 pound self moving through my office won’t cause gravity waves. What are required are extremely massive objects moving very rapidly. So when we look to detect gravity waves, we’re looking for solar mass scale objects. In particular, we search for neutron stars, which are between 1.5 and 3 solar masses. We look for black holes, up to several hundred solar masses. And we look for these objects to be moving very rapidly. So when we talk about a neutron star, we’re talking about a neutron star moving at almost the speed of light. In fact, it has to be vibrating at the speed of light, it can’t just be moving, it has to be shaking back and forth very rapidly. So, they’re very unique, very massive cataclysmic systems that we’re searching for.

Fraser: Gravity waves are purely theoretical, right? They were predicted by Einstein, but they haven’t been seen yet?

Dr. Waldman: They’ve not been observed, they’ve been inferred. There is a pulsar system whose frequency is spinning down at a rate consistent with the emission of gravity waves. That’s PSR 1913+16. And that the orbit of this star is changing. That’s an inference, but of course, that’s not an observation directly of gravity waves. However, it’s pretty clear that they have to exist. If Einstein’s laws exist, if General Relativity works, and it works very well at very many length scales, then gravity waves exist too. They’re just very difficult to see.

Fraser: What’s it going to take to be able to detect them? It sounds like they’re very cataclysmic events. Great big black holes and neutron stars moving around, why are they so difficult to find?

Dr. Waldman: There’s two components to that. One thing is that black holes don’t collide all the time, and neutron stars don’t shake about in just any old place. So the number of events that can cause observable gravity waves is actually very small. Now we talk about, for example, the Milky Way galaxy with one event occuring every 30-50 years.

But the other part of that equation is that gravity waves themselves are very small. So they introduce what we call a strain; that’s a length change per unit length. For instance, if I have a yardstick one metre long, and a gravity wave will squish that yardstick as it comes through. But the level that it will squish the yardstick is extremely small. If I have a 1-metre yardstick, it will only induce a change of 10e-21 metres. So it’s a very very small change. Of course, observing 10e-21 metres is where the large challenge is in observing a gravity wave.

Fraser: If you were measuring the length of a yardstick with another yardstick, the length of that other yardstick would be changing. I can see that being difficult to do.

Dr. Waldman: Exactly, so you have a problem. The way we solve the yardstick problem is that we actually have 2 yardsticks, and we form them into an L. And the way we measure them is to use a laser. And the way that we have arranged our yardstick is actually in a 4-km long “L”. There’s 2 arms, each one’s 4 km long. And at the end of each arm there’s a 4-kg quartz test mass that we bounce lasers off of. And when a gravity wave comes through this “L” shaped detector, it stretches one leg while it shrinks the other leg. And it does this at say 100 hertz, within audio frequencies. So if you listen to the motion of these masses, you hear a buzzing at 100 hertz. And so what we measure with our lasers is the differential arm length of this large, “L” shaped interferometer. That’s why it’s LIGO. It’s the Laser Interferometer Gravitational-Wave Observatory.

Fraser: Let’s see if I understand this correctly. Billions of years ago a black hole collides with another and generates a bunch of gravity waves. These gravity waves cross the Universe and wash past the Earth. As they go past the Earth, they’re lengthening one of these arms and they’re shrinking the other one, and you can detect this change by that laser bouncing back and forth.

Dr. Waldman: That’s right. The challenge, of course, is that that length change is extremely small. In the case of our 4km interferometers, the length change that we measure right now is 10e-19 metres. And to put a scale on that, the diameter of an atomic nucleus is only 10e-15 metres. So our sensitivity is subatomic.

Fraser: And so what kinds of events should you be able to detect at this point?

Dr. Waldman: So that’s actually a fascinating area. The analogy we like to use is like it’s looking at the Universe with radio waves was to looking at the Universe with telescopes. The things you see are totally different. You’re sensitive to a totally different regime of the Universe. In particular, LIGO is sensitive to these cataclysmic events. We classify our events into 4 broad categories. The first one we call bursts, and that is something like a black hole forming. So a supernova explosion occurs, and so much matter moves so rapidly that it forms black holes, but you don’t know what the gravity waves look like. All you know is that there are gravity waves. So these are things that happen extremely rapidly. They last for 100 milliseconds at the most, and they come about from the formation of black holes.

Another event we look at is when two objects are in orbit with each other, say two neutron stars orbiting each other. Eventually the diameter of that orbit decays. The neutron stars will coalesce, they will fall into each other and form a black hole. And for the very last few orbits, those neutrons stars (keep in mind they’re objects that weigh 1.5 to 3 solar masses), are moving at large fractions of the speed of light; say 10%, 20% of the speed of light. And that motion is a very efficient generator of gravity waves. So that’s what we use as our standard candle. That’s what we think we know exists; we know they’re out there, but we aren’t sure how many of them are going off at any one time. We’re not sure what a neutron star in spiral looks like in radio waves, or x-rays, in optical radiation. So it’s a little bit difficult to calculate exactly how often you’ll see either an in-spiral or a supernova.

Fraser: Now will you be able to detect their direction?

Dr. Waldman: We have two interferometers. In fact we have two sites and three interferometers. One interferometer is in Livingston Louisiana, which is just north of New Orleans. And our other interferometer is in eastern Washington state. Because we have two interferometers, we can do triangulation in the sky. But there is some uncertainty left in where exactly the source is. There are other collaborations in the world that we work with quite closely in Germany, Italy, and Japan, and they also have detectors. So if multiple detectors in multiple sites see a gravity wave, then we can do a very good job in localizing. The hope is that we see a gravity wave and we know where it comes from. We then tell our radio astronomers colleagues and our x-ray astronomer colleagues, and our optical astronomer colleagues to go look at that portion of the sky.

Fraser: There are some new large telescopes on the horizon; overwhelmingly large and gigantically large, and Magellan… the big telescopes coming down the pipe with fairly large budgets to spend. Let’s say that you can reliably find gravity waves, it’s almost like it adds a new spectrum to our detection. If large budgets were put into some of these gravity wave detectors, what do you think they could be used for?

Dr. Waldman: Well, as I said before, it’s like the revolution in astronomy when radio telescopes first came online. We’re looking at a fundimentally different class of phenomena. I should say that the LIGO laboratory is a fairly large laboratory. We’re over 150 scientists working, so it’s a large collaboration. And we hope to collaborate with all of the optical and radio astronomers as we go forward. But it’s a little difficult to predict what path that science will take. I think if you speak to a lot of general relativists, the most exciting feature of gravity waves is that we’re doing something called Strong Field General Relativity. That is all the General Relativity you can measure looking at stars and galaxies is very weak. There’s not a lot of mass involved, it’s not moving very fast. It’s at very large distances. Whereas, when we’re talking about the collision of a black hole and a neutron star, that very last bit, when the neutron star falls into the black hole, is extremely violent and probes a realm of general relativity that just isn’t very accessible with normal telescopes, with radio, with x-ray. So the hope is that there are some fundamentally new and exciting physics there. I think that’s what primarily motivates us is, you could call it, fun with General Relativity.

Fraser: And when do you hope to have your first detection.

Dr. Waldman: So the LIGO interferometers – all three interferometers – that LIGO operates are all running at design sensitivities, and we are currently in the middle of our S5 run; our fifth science run, which is a year-long run. All we do for a year is try to look for gravity waves. As with a lot of things in astronomy, most of it is wait and see. If a supernova doesn’t explode, then we’re not going to see it, of course. And so we have to be online for as long as possible. The probibility of observing an event, like a supernova event, is thought to be in the region of – at our current sensitivity – it’s thought that we’re going to see one every 10-20 years. There’s a large range. In the literature, there are folks who claim that we will see multiple per year, and then there are folks who claim that we won’t see any ever at our sensitivity. And the conservative middle ground is once every 10 years. On the other hand, we’re upgrading our detectors as soon as this run is over. And we’re improving the sensitivity by a factor of 2, which would increase our detection rate by a factor of 2 cubed. Because sensitivity is a radius, and we’re probing a volume in space. With that factor of 8-10 in detection rate, we should be seeing an event once every year or so. And then after that, we’re upgrading to what’s called Advanced LIGO, which is a factor of 10 improvement in sensitivity. In which case we will almost definitely be seeing gravity waves once every day or so; every 2-3 days. That instrument is designed to be a very real tool. We want to do gravity astronomy; to be seeing events every few days. It’ll be like launching the Swift satellite. As soon as Swift went up, we started seeing gamma ray bursts all the time, and Advanced LIGO will be similar.

In the past, astronomers could only see the sky in visible light, using their eyes as receptors. New technologies extended their vision into different spectra: infrared, ultraviolet, radio waves, x-rays and gamma rays. But what if you had gravity eyes? Einstein predicted that the most extreme objects and events in the Universe should generate gravity waves, and distort space around them. A new experiment called Laser Interferometer Gravitational Wave Observatory (or LIGO) could make the first detection of these gravity waves.
Continue reading “Podcast: See the Universe with Gravity Eyes”

Artist impression of a gamma ray burst exploding near the Earth. Image credit: NASA. Click to enlarge.
We live in a dangerous Universe. Our tiny home planet is at risk from many extraterrestrial threats: asteroid strikes, solar flares, rogue black holes, supernovae. Now add gamma ray bursts to the list – those most powerful explosions in the Universe. Even 10 seconds of radiation from one of these events would be a deadly setback to life on Earth. Before you start looking for another planet to live on, Dr. Andrew Levan from the University of Hertforshire is here to explain the probilities of a nearby explosion. It looks like the odds are in our favour.

Listen to the interview: We’re Safe From Gamma Ray Bursts (6.0 MB)

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Fraser Cain: Now, I want to learn how safe I am from gamma ray bursts, but first can you give the explainer on what these explosions are?

Dr. Andrew Levan: Gamma ray bursts were really a mystery for much of the last 30 years. They were first discovered in 1967 by satellites which were launched to search for evidence of nuclear tests going on in space. So in the 1960s there was worry on both sides – the Russians and the Americans – we’re worried that the opposing side might be testing nuclear weapons somewhere in space. And so there was a test ban treaty that banned this and then various satellites were launched to be able to detect the signature of these tests. And these tests would have given a signature that would have been a bursts of gamma rays. And so the satellites were launched to search for this. They never actually saw any gamma rays from nuclear tests, but what they did find were these very bright explosions that were happening nowhere in the Solar System. Not associated with anything that was happening that was obvious; not really the Moon or any of the planets or anything like that. And so these were the first discovered gamma ray bursts.

For most the next 20 or 30 years, that was really all that we knew about them; these strange unexplained flashes of high energy radiation. This is light with wavelengths much shorter than X-rays that medical images use. And they were very difficult because of that to pinpoint them. So we really didn’t know where they were, whether they were anywhere near us or whether they were a long way away. And then in the late 1990s, finally we succeeded in pinpointing their origin by optical emissions, by normal light, and that showed that they were incredibly bright explosions which happen in the distant Universe, so you’re talking about looking right back to only a few hundred million years after the Big Bang – 95% of the way back through the age of the Universe.

And so, that was sort of the first breakthrough. And then over the next few years, it was realized that these gamma ray bursts were actually caused by the collapse of a very massive star. So when you’re talking very massive, you’re actually talking about 20-30 times as heavy as the Sun. And what happens with these stars is that they burn, or fuse, hydrogen into heavier elements at their cores. And eventually that process stops, they fall into themselves, form a black hole, and it’s that process which creates a gamma ray burst.

Fraser: That sounds very similar to the process of a supernova explosion. So, what’s the difference?

Dr. Levan: Well indeed, many gamma ray bursts are supernova explosions. So they are just a subset of supernova. Supernova happen when stars more massive that 8 times the mass of the Sun run out of nuclear fuel and collapse, but most of the time they form a neutron star rather than a black hole. Now a neutron star is just slightly less extreme an object, but it’s still very extreme. And so it is more or less the mass of the Sun, but collapsed into a region only 10 miles across. But what happens there is that you actually get a lot less energy out. And so when you have these very massive stars that become gamma ray bursts, the energy from these gamma rays is launched in a jet. So it’s like a hosepipe being pointed straight at you, and it goes basically out the poles of the star at either end. It illuminates the sky as a very bright source. But it only illuminates perhaps a few percent of the sky. And that is where the gamma rays are emitted, and that’s what makes a gamma ray burst. And only a few types of supernova are those which create both the black holes and the necessary conditions to create a jet are those that create the gamma ray burst. And then the gamma ray bursts are much much brighter than the normal supernovae that we see.

Fraser: And being nearby these is a pretty dangerous place to be. How risky is it, and how far out is the sphere of destruction?

Dr. Levan: People talk about supernovae and they talk about gamma ray bursts as being dangerous to the Earth. For a supernova, it really has to be very close; it has to be within about 10 parsecs of us (or 30 light-years). There really aren’t very many stars in that. Now with gamma ray bursts is so much more luminous that it could be 30 or 40,000 light years away from us. So that’s halfway across the galaxy. If one went off in the centre of the galaxy and it hit the Earth, then that would be an incredibly dangerous thing for us. Because what would happen is the high energy radiation would hit us would ionize the high atmosphere and create lots of new, quite nasty, nitrogen oxides which would create acid rain. It would destroy the ozone layer, and at the same time, it would shower the side of the Earth facing it with an incredibly high dose of ultraviolet radiation.

Fraser: If one of these goes off in your galaxy, that’s a huge setback for life. I can’t imagine much that could withstand that, apart from the microbial life underground.

Dr. Levan: Yes, absolutely, it really does. The impact for us is that you would have the rather paradoxical situation that the nitrogen oxides that were created in the atmosphere could actually block the optical light, so you’d have global cooling. You’d have problems with plants photosynthesizing and stuff like that. But at the same time because you have the ozone layer being destroyed, you’d have a high flux of ultraviolet light that would really be damaging to any life that encountered it. And so it would drastically affect the process of evolution. Whether it would be possible for us to evolve sufficiently to live through that is very unlikely.

Fraser: Do scientists think that’s responsible for some extinction events in the past?

Dr. Levan: There’s been a lot of discussion about this. Obviously the most talked about extinction is that of the dinosaurs and a lot of people now believe that it was probably an asteroid hit from outside the Earth or something like that. There certainly was an extinction event about 400 million years ago which people have talked about perhaps being due to a gamma ray burst. Obviously it’s very uncertain when you look back and you’re trying to look through the fossil record, but certainly gamma ray bursts have been talked about because of the fact that they’re less common than supernova, they can affect you over such a big volume the Earth that people have talked about past extinctions being due to gamma ray bursts.

Fraser: Okay, now I’ve been promised some good news. Lay it on me.

Dr. Levan: What we’ve done is study a lot of these bursts, about 40 of them. Now these are gamma ray bursts that you can relax, they’re so far away that they’re actually difficult to see with even the biggest telescopes in the world. But what we can study from them is the type of galaxy in which they happen. And so the Milky Way, which is our galaxy, is called a grand design spiral. It’s a great big, very massive galaxy. Now when you look at the types of galaxies these tend to occur in, you find that they’re always in these small, messy, very irregular galaxies which have a very low mass, which are very unlike the Milky Way. And the reason for this is that the Milky Way has lots of what we call metals. Now when astronomers talk about metals, we don’t really mean things like aluminum or iron, or things like that. We really mean anything heavier than hydrogen or helium. And so in order to have life, you have to have carbon and oxygen and things like that which are very rare in the little galaxies that have gamma ray bursts going off. And so what you realize when you look at it is that little galaxies are vital to creating gamma ray bursts because what you need basically is very massive stars that form black holes, and it’s much easier to do that in these little galaxies that have very few metals. And what that essentially means is that although we’ve had that in the past, gamma ray bursts just don’t happen in galaxies like our own.

Fraser: I know that some recent research shows us some star forming regions in nearby satellite galaxies to the Milky Way that are building up stars that are 50-80 times the mass of the Sun, so are those good candidates or is there something about the heavier elements?

Dr. Levan: Yes, so there’s something very specific about the heavier elements. When you have heavier elements in a star, it actually effects the evolution of the star very fundamentally. And so what happens is that these heavy elements have what we call stellar winds; quite strong stellar winds. And what this means is that they push off all of the material that’s outside them. So although they start their lives as very massive stars, by the time they end their life, they’ve actually lost much of that mass that they’re no longer massive enough to form black holes. And so they actually form these neutron stars as normal supernovae. So there’s very little doubt that these massive stars that you see and the massive star forming regions that you see are going to form supernovae, because they’re much further away, they’re no threat to us. And because of their stellar winds, they will lose so much of their mass that they can’t make black holes and so they can’t make gamma ray bursts.

Fraser: Since all of the gamma ray bursts have been seen across the Universe, is it almost like a function of age – as you look further away, you’re looking back in time. We used to have gamma ray bursts, but they just don’t happen anymore.

Dr. Levan: Yes, very much so. Obviously, as stars evolve, you make your first generation of stars. All of the metals, all of the atoms that you see around you, in your body, in the building, and everything like that, are made from supernova explosions in the past. They enrich everything around them, and then there’s another generation of stars that are made from that, and so on. And so when you look back into the Universe, there were less of these metals around, and less of these heavy elements, and so the early Universe is a much more promising place to look for gamma ray bursts than the Universe as we see it now where only gamma ray bursts occur in little galaxies where there hasn’t been so much star formation for so long as there has been in the Milky Way.