Category: Podcasts

Artist illustration of the Atacama Large Millimeter Array currently under construction. Image credit: ESO. Click to enlarge.
Listen to the interview: Get Ready for Deep Impact (4.8 MB)

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Fraser Cain: Can you give me some background on the submillimeter spectrum? Where does that fit?

Paul Ho: The submillimeter, formally, is at a wavelength of 1 millimeter and shorter. So 1 millimeter wavelength in frequency corresponds to about 300 gigahertz or 3×10^14 hertz. So, it is a very short wavelength. From that down to a wavelength of about 300 microns, or a third of a millimeter, is what we call the submillimeter range. It is sort of what we call the end of the atmospheric window as far as the radio is concerned, because shorter, about a third of a millimeter they sky becomes essentially opaque due to the atmosphere.

Fraser: So, these are radio waves, like what you’d listen to on the radio, but much shorter – nothing I could ever pick up on my FM radio. Why are they good for viewing the Universe where it’s cold?

Ho: Any object that we know of, or see, typically is radiating a spread of energy characterizing the materials that we’re talking about, so we call this a spectrum. And this energy spectrum typically has a peak wavelength – or the wavelength at which the bulk of the energy is radiated. That characteristic wavelength depends on the temperature of the object. So, the hotter the object, the shorter the wavelength comes out at, and the cooler the object, the longer the wavelength comes out at. For the Sun, which has a temperature of 7,000 degrees, you’d have a peak wavelength which comes out in the optical, which is of course why our eyes are tuned to the optical, because we live near the Sun. But as the material cools, the wavelength of that radiation gets longer and longer, and when you get down to a characteristic temperature of say 100 degrees above Absolute Zero, that peak wavelength comes out somewhare in the far infrared or submillimeter. So, a wavelength on the order of 100 microns, or a little bit longer than that, which puts it into the submillimeter range.

Fraser: And if I were able to swap out my eyes, and replace them with a set of submillimeter eyes, what would I be able to see if I looked up into the sky?

Ho: Of course, the sky would continue to be quite cool, but you’d begin to pick up a lot of things that are rather cold that you would not see in the optical world. Things like materials that are swirling around a star which are cool, on the order of 100 Kelvin; pockets of molecular gas where stars are forming – they would be colder than 100 K. Or in the very distant, early Universe when galaxies are first assembled, this material is also very cold, which you would not be able to see in the optical world, that you might be able to see in the submillimeter.

Fraser: What instruments are you using, either here or in space?

Ho: There are ground and space instruments. 20 years ago, people began to work in the submillimeter, and there were a few telescopes that were beginning to operate in this wavelength. In Hawaii, on Mauna Kea, there are two: one called the James Clerk Maxwell Telescope, which has a diameter of about 15 metres, and also the Caltech Submillimeter Observatory, which has a diameter of about 10 metres. We have built an interferometer, which is a series of telescopes which are coordinated to operate as a single instrument on top of Mauna Kea. So 8 6-metre class telescopes which are linked together and can be moved apart or moved closer together to a maximum baseline of, or separation, of half a kilometre. So this instrument is simulating a very large telescope, on the size of half a kilometre at its maximum, and therefore achieving a very high angle of resolution compared to existing single element telescopes.

Fraser: It’s much easier to combine the light from radio telescopes, so I guess that’s why you’re able to do that?

Ho: Well, the interferometer technique has been used in radio for quite some time now, so we have perfected this technique fairly well. Of course, in the infrared and optical, people are also beginning to work in this way, working on interferometers. Basically, combining the radiation, you have to keep track of the phase front of the radiation coming in. Normally I explain this as if you had a very large mirror and broke it so you just reserve a few pieces of the mirror, and then you want to reconstruct the information from those few pieces of mirror, there are a few things you need to do. First, you have to be able to keep the mirror pieces aligned, relative to each other, just like it was when it was one whole mirror. And second, to be able to correct for the defect, from the fact that there’s a lot of missing information with so many pieces of mirror that are not there, and you’re only sampling a few pieces. But this particular technique called aperture synthesis, which is to make a very large aperture telescope by using small pieces, of course, is the produce of Nobel prize winning work by Ryle and Hewish some years ago.

Fraser: What instruments are going to be developed in the future to take advantage of this wavelength?

Ho: After our telescopes are built and we’re working, there will be an even larger instrument that’s being constructed now in Chile called the Atacama Large Millimeter Array (ALMA), which will consist of many more telescopes and larger apertures, which will be much more sensitive than our pioneering instrument. But our instrument will hopefully begin to discovery the signs and the nature of the world in the submillimeter wavelength before the larger instruments come along to be able to follow along and do more sensitive work.

Fraser: How far will those new instruments be able to look? What could they be able to see?

Ho: One of the targets for our discipline of submillimeter astronomy is to look back in time at the earliest part of the Universe. As I mentioned earlier, in the early stage of the Universe, when it was forming galaxies, they tend to be much colder in the early phases when galaxies were being assembled, and it will radiate, we think, principly in the submillimeter. And you can see them, for example, using the JCM telescope on Mauna Kea. You can see some of the early Universe, which are very highly redshifted galaxies; these are not visible in the optical, but they are visible in the submillimeter, and this array will be able to image them, and locate them very actively as to where they are located in the sky so that we can study them further. These very early galaxies, these early formations, we think are at very high redshifts – we give this number Z, which is a redshift of 6, 7, 8 – very early in the formation of the Universe, so looking back to perhaps 10% of the time when the Universe was being assembled.

Fraser: My last question for you… Deep Impact is coming up in a few weeks. Will your observatories be watching this as well?

Ho: Oh yes, of course. The Deep Impact indeed is something we’re interested in. For our instrument, we have been studying Solar System type bodies, and this includes not only the planets, but also the comets as they come close or impact, we expect to see material to spew off, which we should be able to track in the submillimeter because we’ll be looking not only at the dust emissions, but we will be able to watch the spectral lines of the gasses which come out. So, we’re expecting to be able to turn our attention to this event, and to also be imaging it.

Paul Ho is an astronomer with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Deep Impact’s impactor module on a collision course with Comet Tempel 1. Image credit: NASA/JPL. Click to enlarge.
Listen to the interview: Get Ready for Deep Impact (6.1 MB)

Or subscribe to the Podcast: universetoday.com/audio.xml

Fraser: Can you give me a preview for what we’re going to be seeing on July 4th?

Dr. Lucy McFadden: I wish I knew exactly what was going to happen on July 4th, but this is an experiment. I can tell you what we think we might see, but chances are it may be significantly different.

So, we have a spacecraft on its way to Comet Tempel 1, which is a short-period comet that orbits – comes into the inner solar system – about once every 5.5 years. It is about the size of Washington DC. It can be fit into the area of Washington DC, but it’s a little bit elongated. It’s about 14 km by 4 km by 4 km, and as our spacecraft is heading toward it, we have planned to actually separate the spacecraft into two parts. Let me set the stage here, this comet is in orbit around the Sun. It’s coming to its closest point of the Sun, called its perihelion, and thus be moving at its fastest speed through the solar system in early July. Our spacecraft is also in orbit around the Sun, and it’s heading to intercept the orbit of the comet. 24 hours before we plan to impact this comet, we’re going to separate the two spacecraft, the impactor and the flyby. The impactor will continue on its collision course to the comet, and the flyby – or mother ship – will slow down a little bit and change its direction ever so slightly so that it will be able to watch as the impactor hits the comet. When it hits the comet, when we have this cosmic collision in space, what’s going to happen is the energy of the impact is going to propagate into the comet itself, in the form of a shock wave. This shock wave will plough into the comet; how deep, we don’t know. But at some point, the force of the material in the comet itself will push back on the advancing energy shock wave and push material out of the comet. We will have formed a crater with ejected material coming out of the hole that we created.

Now, you may ask, why are we doing this? We’re doing this to take a look – to take advantage of the opportunity of this comet being so close to us – to take a look at the inside of the comet; to see what the inside is made of, and see what structure is there.

To elaborate more, I think I need to give you some perspective on what comets are, and what they are in the solar system. I like to say they’re the oldest and coldest part of the solar system. They formed at the edges of the solar system, hundreds of thousands of times the distance that the Earth is from the Sun. So, everything where comets formed is cold. They also formed 4.5 billion years ago, when the solar system was forming. They have never been incorporated into a planet. So they’re both old and cold as well. We’re taking advantage of the comets coming closer to the Earth to use it as a laboratory and as a probe to distant edges of the solar system in both space and time.

Fraser: Now, Deep Impact only launched a couple of months ago, so did we get really lucky with Tempel 1 being at the wrong place at the right time?

Dr. McFadden: Yeah, well, from my perspective it was at the right place at the right time.

Fraser: I was more looking from the perspective of the comet.

Dr. McFadden: Let me say two things here. First of all, the comet isn’t going to be harmed. Let’s get some perspective here in terms of the mass of the spacecraft versus the mass of the comet. Or the energy of the spacecraft versus the energy of the comet in motion. It’s equivalent to a gnat, or a small mosquito being run into by a 767 aircraft. So, we’re not going to hit the comet. But, needless to say, I’ll let you take the perspective of the comet if you want. But yes, it was in the right place, or the wrong place, at this time. NASA said, when it issued its announcement of opportunity for space exploration missions, they said that this announcement covers money available within a certain time frame, and the time frame was between 2000 and 2006. And so, we went looking for comets that were available during the time NASA would give us money, and then when we found Comet Tempel 1 close to perihelion, when it’s moving fastest, that also pleased us because the faster the comet’s moving, the more energy involved in the transfer to create the crater. So, it’s good from that point of view. And then there’s a third, but secondary reason why Comet Tempel 1 is good; it’s not as active as some comets might be. There’s not as much dust and jet activity associated with Comet Tempel 1, which might be confusing or make it hard for us to actually observe the formation of the crater when we hit it. So, Comet Tempel 1 fits.

Fraser: How are we going to be observing it from here on Earth and from space?

Dr. McFadden: We have the spacecraft observing it from space – our Deep Impact spacecraft. We have the Rosetta spacecraft, which is heading to another comet, will also observe it from space. We have NASA’s three Great Observatories: Chandra, Hubble and Spitzer will be observing it. Three different wavelengths; Chandra’s an X-ray telescope, and Hubble’s an optical and near-infrared imaging telescope. We’ll be observing some spectroscopy with Hubble too. And then Spitzer’s an infrared telescope. So, we’ll be using those. As well as all the major observatories around the world will be observing the comet, before, during and after impact. So we’re having a worldwide observing campaign.

Fraser: And how will the pictures from Deep Impact compare to the pictures we saw from Stardust?

Dr. McFadden: It’s interesting, I’m using the images from Stardust to practice interpreting the images we get from Deep Impact. We will get a closer look at Comet Tempel 1 than the Stardust spacecraft did; we will be flying closer – we’ll be flying 500 km from Comet Tempel 1, whereas the Stardust spacecraft was 1,100 or 1,300 km distant.

Fraser: I remember that Stardust got hit quite a bit by debris, how will Deep Impact do if it’s going to be closer to the comet?

Dr. McFadden: You have to remember that the main objective of Stardust was to collect dust, so, they wanted to get hit. So they flew into the region with the largest dust density. What we do when we fly through that same region is we turn the spacecraft away into shield mode to protect the telescope during the time when we should be getting the greatest number of hits from dust and debris. And we actually fly at an angle. Most of the debris exists in the plane of the orbit, in the direction of its motion, and so the spacecraft will fly past it at an angle; so there’ll be a short, 20 minute period when we will not be observing to protect the cameras.

Fraser: Once Deep Impact completes its flyby, will you have any additional scientific targets you’d like to be able to use the spacecraft for, once it gets out of visual range of Tempel 1?

Dr. McFadden: There are currently no specific plans for observing in a follow-on mission; that has to be approved by NASA. We have done some research and know that there are another comet or two that we could observe, but we haven’t gotten approval for that yet.

Fraser: So, in your wildest dreams, what will turn up on July 4th?

Dr. McFadden: Well, my wildest dream is that the impactor will go into the comet and come out the other side, but that’s not very likely.

Fraser: Okay then, maybe a less wild dream.

Dr. McFadden: Okay, less wild, in order of probability is that the comet will have the consistency of a brick, for example, and the impactor will hit it and not do much damage to the surface, or not really create much of an impact because the comet is the consistency of a brick. But that’s not very likely either. On the other extreme, what if the comet is like Corn Flakes? If it’s like Corn Flakes, we should get a spectacular display of ejecta. We call it an ejecta curtain during the formation of the crater, and I’m hoping that that’s what we’ll see, because that would be very dramatic. And hopefully we could watch as we’re taking fast pictures with very short exposures repeatedly. We’ll be clicking as we go by. If we have a big ejecta curtain, we should be able to see the ejecta form, or traveling along in space, and that will allow us to determine the most information about the internal structure of the comet itself. So that’s what I’m hoping will happen.

NASA Astronaut B612 Foundation director Dr. Edward Lu. Image credit: NASA
Listen to the interview: Homing Beacon for an Asteroid (6.2 mb)

Or subscribe to the Podcast: universetoday.com/audio.xml

Fraser Cain: Can you give me some background on the development of the B612 Foundation?

Dr. Edward Lu: It all started a few years back with a couple of different conversations I had with Piet Hut at the Institute for Advanced Studies, and a former astronaut called Rusty Schweickart. We were discussing the advances in high specific impulse propulsion, in other words ion propulsion or plasma propulsion, which is currently being worked on at NASA. We wondered, what could you use this for? One of the things that I’d been thinking about and discussed with various other people was the idea of pushing on an asteroid to demonstrate how this would work; to actually have a mission that would need this technology and would therefore drive you to complete the technology. Having a direct goal is the best way to get you to actually build something. The idea of moving an asteroid that something we’re eventually going to need to do, which is something that’s not possible using current chemical rockets. So we talked about that, and eventually we organized a meeting here at NASA of folks who work in the area of asteroids or working on spacecraft development. That was about 3-4 years ago. Everyone came down to NASA in Houston, and we talked about the idea and what it would take; how much thrust you would need, how much power you would need, how you could do such a thing. Our little foundation was an outgrowth of that meeting.

Fraser: You’ve set your sights on an asteroid that’s going to be swinging past the Earth in a couple of decades.

Lu: This is a proposal that’s been put forth by Rusty. This is an asteroid called 2004 MN4, which is going to make a very close flyby of the Earth in the year 2029 – it’s actually going to be about 4 Earth radii away, below the altitude of our geosynchronous satellites. It’s going to pass so close to the Earth that it’s going to take a pretty sharp bend in its trajectory. The problem is that where it goes after this flyby is really critically dependant on how close it comes to the Earth. It’s like a banked billiard shot. If you make a small error in a banked shot and you can have a big error where the ball goes after bouncing off of another ball. And that’s exactly what’s going on here. It turns out that our best guess at where it’s going to be when it comes by the Earth means that if there is a chance that 6-7 years later – either 2035 or 2036 – this thing could come back and actually hit the Earth. Now the chances are really small because we don’t have very good information on how close it’s going to be to the Earth. We only know its distance, how close it’s going to come to the Earth, by a factor of some thousands of miles. In order to know whether it’s going to come back and hit the Earth, you need to know accurately how close it’s going to come to the Earth to withing a factor of a few hundred metres, less than a kilometre. That’s why the best we can say is, oh, there’s some chance that it could hit us, but we just can’t simply say any better. What Rusty pointed out is that as the years go by, running up to 2029, this asteroid is going to go basically on the other side of the Sun. Its orbit is going to be on the other side of the Sun for some period of time. We’re going to lose track of it here in the next year or so. In which case, we won’t be able to pick it up again for another 6-7 years when it’s no longer orbiting the Sun, but on the other side of it. Its orbit will bring it back around our side of the Sun and we’ll pick it up again, and by then we’ll be able to determine its orbit more accurately, but the question is, will it be accurate enough to determine whether or not – after this slingshot when it comes by the Earth in 2029 – it will come hit us later.

Fraser: And you’re hoping if you can put some kind of tracking on the asteroid, then you’d be able to get it down within that few hundred metres distance.

Lu: Exactly, and the reason Rusty pointed out that’s it’s important to do it early is because, what if you find out that it is going to come back and hit us? If you’re going to do something about it, you would need to do something about it before 2029, before the close pass. And the reason is, again going back to a billiard shot, let’s say you’re taking a cue ball and trying to shoot it straight into a corner pocket. You can be a bit off in your aim and you can still hit that pocket pretty well. But not if you’re trying to hit another ball into the corner or do a bank shot where the cue ball bounces off something and then goes into the corner. Even a small error can mean you’re going to miss. So that’s both good and bad. If this thing is on a collision course, before 2029 you can upset it and keep it from going on a collision course by a very small change in its velocity. After 2029, it becomes very hard, in fact, more than likely not possible.

Fraser: I guess that’s one of my concerns in general about this whole process of detecting asteroids is that it’s all a world of probabilities. It’s not like it’s absolutely going to hit us on this date or anything. These are the chances of this asteroid, and those are the chances of that asteroid, and I wonder…

Lu: Well, it’s not really a matter of probability, that’s kind of a misnomer. Each one of these things either is going to hit us or it won’t. The reason you call it probability is because we can’t measure its exact trajectory well enough to say yes or no. That’s why we list it as probability. In the same way as: will it rain tomorrow. They say 30% chance of precipitation. It either is or isn’t going to rain, it’s just that we can’t tell you. In essence it’s like a weather forecast. And the accuracy with which you can measure the orbit, or the accuracy you can tell the weather, tells you how accurate your forecast is going to be. The forecast probability has nothing to do with the asteroid itself, it’s solely a matter of our telescopes.

Fraser: Right, and our techniques. What kind of mission would be involved to actually reach out and tap the asteroid?

Lu: First off, what’s actually been proposed is not to actually move it yet because the chances are that you won’t have to do it. What he’s actually proposing is that you put something on it that just simply measures where it is so you can tell for sure whether or not it’s going to hit or not. You want to know that early enough so that if it actually was coming, then you could do something about it. That’s what’s behind the idea of putting a transponder; all that is is a radio transmitter that you can measure exactly where it is. If you had to move it, that’s a whole other issue. But, the first thing is to know whether or not it’s even an issue or not.

Fraser: And so, what kind of mission would be involved to actually put the transmitter on the asteroid?

Lu: That’s something that would be a relatively simple mission, meaning all you have to do is get into the vicinity of it. You don’t even have to put down on it. Although, if you’re already going there, you might as well make this thing a very productive scientific mission because there’s plenty of things we can learn about asteroids. We’ve never visited a small asteroid. We’ve sent probes to much larger asteroids, hundreds of miles across, versus this one which is actually very small compared to those other ones – just a little over 300 metres across. Never having seen one of these things up close, obviously it could be a great scientific mission. What Rusty’s pointed out is that you kind of get two things here: number one, in the very unlikely case that this thing is going to hit us, this’ll tell you whether or not it will (more than likely not); but, if in fact it is not going to hit us, you have still put a very scientifically interesting mission out there. You can see what this thing is made of, what its surface structure is like, what it might be like to land on one of these things later, if you have to move another one. It tells you a lot about the properties of asteroids, so this thing doesn’t go to waste if you find, as it likely, that it’s not going to hit you.

Fraser: And what kind of time frame would you want to be able to launch it by?

Lu: You’d want to put it up something around the 2012/2013 time frame. And the reason is, again, you need lead time. Let’s say you put it up there in 2012 or 2013 and it takes a year or so to get there, and then you know within a year or so after that it is or isn’t going to hit you. Let’s say that you found out that it was going to hit you; well now it’s like 2015 at this point, and that gives you substantial 14 years to do something about it, before the close approach in 2029. Now you’re talking a much more ambitious mission, you’re talking a mission where you’re actually going to go push on this thing. That’s why you need the lead time. Something like that has never been tried before. It’s not something you can have an off the shelf spacecraft and say, well, we’ll just go ahead and launch it. It’s going to take some years to prepare the spacecraft, get it ready to launch, test it, and then fly it.

Visit the B612 Foundation Website

Artist illustration of an extrasolar planet. Image credit: CfA. Click to enlarge.
Listen to the interview: Microlens Planet Discovery (6.2 mb)

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Fraser Cain: Can you give me some background on the planet that you helped to discover?

Grant Christie: There’s still a bit of analysis to do on it to figure out exactly all its parameters, but it’s in the order of about 15,000 light-years away. That’s still being worked on, the distance. It’s quite a massive planet, probably in the order of about 2-3x the mass of Jupiter, and it’s orbiting at about 3 astronomical units away from its parent star. It’s not exactly like a familiar object, but if you could see it up close, it would probably look a bit like Jupiter. It would be about 3 times heavier, but not that much bigger because it would be more compressed by its gravity.

Fraser: The planets that have been discovered to date are within a few hundred light years of Earth. How were you able to find one 15,000 light-years away, expecially using backyard equipment?

Christie: With this discovery, we’re just part of a cog in a wheel, we’re part of a team, but it was using a method known as gravitational microlensing. That sounds like a bit of a mouthful, but essentially it uses a star as a lens to magnify a more distant star. This works if the two stars are exactly lined up as we see them from Earth. So we have a situation where we have a distant star somewhere in the halo – or the bulge – of the galaxy maybe 20,000 light-years from Earth. By chance, another star has come almost exactly in line between us and it. That intervening star’s gravity works like a lens and it amplifies the light of the more distant star. We can’t see them as two stars, they’re so close together, and no telescope on Earth can. But what we see is the magnification, or the amplification of the light from the distant star as it goes through that lens. All of that’s fine, some 600 of these microlensing events are detected each year currently. They in themselves aren’t that unusual, but it turns out that if you have a planet orbiting the lensing star – the one that’s intervened between us and the more distant one – then that planet hugely changes the characteristics of the lens. It changes the light amplification greatly. What we’re doing is simply measuring the brightness changes of the lens as these two stars come into alignment and then move out of alignment. It turns out that the one we were observing, the light was magnified by something like 50x over and above what was there before the lensing started. That brings faint stars that we normally couldn’t see with a small telescope up within our range. In the current case, the amplification brought it up to magnitude 18 in the visual wavelengths. That’s very close to our limit, but we were still able to do it.

Fraser: Was your team expecting to find evidence of a planet before you began any observations, or was that just a happy outcome?

Christie: It is largely a happy outcome. There’s a team based in Chile, a Polish team from Warsaw University let by Professor Udalski, and their job, their main function is to find microlensing events. They monitor millions of stars every night looking for stars that just seem to rise in brightness in a way that you’d expect from a lens. There are obviously lots of variable stars as well, which they have already tabulated, so they know about those. They’re detecting microlensing events. They’re detecting about 600 a year. They started observing this event in about March 17th, or thereabouts, and they noticed this star just starting to brighten – it had never brightened before – and they followed it. Each night as they took an observation, it appeared to brighten more and more, and as this process goes on they noticed that it was following a particular brightening curve that you’d expect from a microlensing event, so they were confident that it was a microlens. And then as we got closer into April, it started to show signs that it was departing from a pure simple lens you’d get from a single star all by itself; that’s a mathematically defined shape and if the photometry’s good, you can usually tell whether you’ve got a single lens or not. Around April 18th they started to notice a significant departure from that simple lens model, these are the guys running the OGLE team. They put out an alert that went to MicroFUN, who is a group we’re associated with. They run out of Ohio State University, led by Professor Andrew Gould there. We then received notification saying, it looks like there might be an anomoly with this microlensing event; try and observe it as much as possible. That’s really where we started our observations. By that stage it was faint, but it was still within reach of our telescopes. We were surprised that it actually was observable. I would have thought that it was too faint. Now I know that we can do work at a fainter limit than I’d previously thought. It was known by about April 20th that this microlensing event had a strong anomaly in it, which is the term they use, and we followed it for the following few days – probably about 3-4 days. It went through some very strong anomalies that really were a sign that was a planet present causing those anomolies. Most of these events you observe – I’ve done quite a few, probably 20 at least myself – turn out to be a simple lens, and there’s nothing surprising in them at all. The excitement of doing this sort of work is that you simply don’t know, nobody knows what you’re going to find. You start following one of these microlensing events as it reaches its maximum, and it’s at the maximum point, or close to it when the maximum sensitivity to a planet is going to be. We’re just not that interested in looking at them until you get very close to that maximum. And that’s when the networks really come are really start to saturate the light curve by covering them.

Fraser: So the stars have to be lined up quite nicely for the effect of the planet to show up.

Christie: Yes, they need to be nearly perfect. That creates a very high amplification. Some of the ones we’ve looked at have had amplifications where the light is magnified 800x. They’re not common, but when you get a very high amplification lens like that, when the alignment is nearly perfect, that’s when you’re most likely to find a planet if there’s one present.

Fraser: How sensitive can this technique be?

Christie: Some of the experts have said that had this planet not been bigger than Jupiter, it was the size of the Earth, these observations still would have detected it. I know there’s some debate about that amongst the academics in the teams, but broadly speaking, that’s probably an indication that this method can be very sensitive. And this event actually didn’t come up to be that bright. We’ve observed ones which have come up so bright you could see them in a little 6″ telescope.

Fraser: That’s amazing, though. I know people have been discussing different techniques that they might be able to see Earth-sized planets orbiting other stars, but to know that we might have a technique available right now is pretty impressive. I wanted to talk to you a bit about how amateurs can get involved in the discoveries in astronomy. Where are some avenues that people can get involved?

Christie: There are lots of ways you can get involved in observational astronomy, but in talking about photometry, which is a measurement of star brightness, you basically just need a telescope with as much aperture as you can afford. A decent sort of mounting and a CCD imaging camera. For below $10,000 you can set up a system that’s very capable, and can actually be really useful. There are lots of other things you can do in observational astronomy that don’t require that, but to do this sort of work, that’s what you’d need. We do work other than this microlensing work, we also measure the light changes of objects called cataclysmic variable stars. These are interesting objects that do a lot of flickering, and all sorts of things, and we’re part of a worldwide network that follows that kind of object. Generally, the common denomenator is the measurement of brightness over time of some star or object. That’s called photometry, and that’s primarily what we do.

Fraser: Congratulations on your team’s discovery of this new planet, and good luck with your work in the future.

Christie: You’re very welcome. I’d like to pay tribute to my co-worker here in New Zealand, Jennie McCormick, who uses the smallest telescope of all, and has done way over a thousand hours on this kind of work and deserves the recognition from her efforts put in.

Artist illustration of a spacecraft passing through a wormhole to a distant galaxy. Image credit: NASA. Click to enlarge.
Listen to the interview: Unlikely Wormholes (4.5 mb)

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Fraser Cain: Now, I’ve watched my share of Star Trek episodes. How well has this prepared me for the actual scientific understanding of a wormhole?

Dr. Stephen Hsu: In Star Trek they don’t really use wormholes, but maybe the best treatment in sci-fi for wormholes was in the movie Contact, which is based on a book by Carl Sagan. And actually historically, when Sagan was writing the novel – Sagan was an astronomy professor – he contacted an expert in General Relativity, a guy named Kip Thorne, at Caltech, and wanted to make sure that the way wormholes were treated in Contact was actually as close to being scientifically correct as possible. And that actually stimulated Thorne to do a lot of research on wormholes. Our work is actually an extension of things that he did.

Fraser: So if you wanted to build a wormhole, theoretically, what would you do?

Hsu: You need to have a very weird or exotic kind of matter and that matter has to have highly negative pressure. It turns out that to stabilize the throat or the tube of the wormhole you need very strange matter and our work has to do with how possible that kind of matter would be in models of particle physics.

Fraser: Let’s say you build a tear in spacetime and you fill it with exotic matter to keep it open, and then you could move the two end points of the wormhole around the Universe and they would connect both in space and in time.

Hsu: But in some science fiction stories they postulate that there are just some wormholes left over from the Big Bang, and we would just discover one and start using it. But the constructive model is that humans, or some alien civilization, actually build their own, and in that case the two ends of the wormhole probably are pretty close together at the beginning but then you pull them apart.

Fraser: Where has your research led you to look at wormholes?

Hsu: We were studying fundamental constraints on something called the “equation of state of matter” – what properties, like pressure or energy density can matter have. We found some very strong constraints, and it turns out those constraints are very negative for the possibility of building a wormhole.

Fraser: What effect will they have on the wormhole?

Hsu: To get the very weird exotic matter that I mentioned before with very negative pressure, it turns out the equations show that when you force the pressure to be that negative, there always some unstable mode in the matter, which means that if you were to bump your apparatus, you might find the exotic matter – which is stabilizing the wormhole – just collapses into a bunch of photos or something.

Fraser: Is it a matter of not bumping your apparatus, or is it theoretically impossible to reach a stable point?

Hsu: I would say it’s theoretically impossible to build classical matter which is stable and can stabilize a wormhole. You might ask, well maybe I’ll just avoid bumping the thing, but if you were to send a person through the wormhole, that itself would provide a bump and would very likely cause the whole thing to fall apart.

Fraser: Let’s say you didn’t want to send people, you just wanted some way of sending information – talking back in time.

Hsu: That’s not excluded. It turns out the constraints we derive have to do with matter in which quantum effects are relatively small. If you have matter in which quantum effects are very big, then you could still have a stable wormhole. The wormhole itself would be fuzzy in a quantum way. The tube of the wormhole would be fluctuating like a quantum state. Now, that doesn’t prevent you from sending a message back in time; you might have to try to send the message many times to get it to go where you want it to go. But, perhaps you could still send a message. Sending a person might be dangerous if the wormhole is fluctuating because the person might end up in the wrong place or the wrong time.

Fraser: I’d heard estimations that building a wormhole would require more energy than the entire Universe. Have you got some kind of calculations to that effect?

Hsu: Our calculations don’t necessarily show that. It does take a tremendous amount of energy density to create a wormhole which is big enough for a human to fit through. But, usually considering this kind of problem, you assume that whatever civilization is trying to do this has arbitrarily advanced technology. What we’re trying to understand is whether there’s a limitation not coming from technology but really coming from the fundamental laws of physics.

Fraser: And where will your research lead you from this point on? Is there something that you’re still a little unsure about?

Hsu: Our result mainly has to deal with the classical wormholes, or wormholes whose spacetime is not very quantum mechanical, and we’re still interested to see if we can extend our results to cover wormholes in which spacetime is fuzzy.

Fraser: There’s some new work on dark energy where they’re saying that the dark energy effect seems to be happening in the Universe, that it’s accelerating. Either there’s a new form of energy that’s not been seen before, or maybe it’s a breakdown in Einstein’s theories at a large level. If some of that work starts to show that maybe Einstein’s relativity isn’t able to explain it at the larger level, will it have an implication on the classical understanding of what a wormhole is?

Hsu: In the context of dark energy, since it’s something that affects the large scale structure of the Universe, the behaviour of the Universe on length scales of megaparsecs, it’s always possible that General Relativity as a theory is modified at very large distances and because we haven’t been able to test it on those distances. So it’s always possible that conclusions you get from Relativity are just not applicable. In our case, the length scale over which we’re using General Relativity is on the size of a human. So, it would be somewhat surprising if General Relativity were to break down already at those length scales, though it’s possible.

Fraser: So it’s more on the small side what you’re looking at. It still explains things quite nicely at this scale.

Hsu: Right, there are stronger experimental tests of General Relativity, or at least Newtonian gravity, on length scales of metres than on megaparsecs. So we’re a little more confident that the mathematical formulation of gravity that we’re using is correct.

Fraser: If I wanted to get across the Universe quite rapidly, I should look perhaps to the warp drive instead, or maybe just plain old moving in regular space.

Hsu: I’m a huge science fiction fan, and have been since I was a kid, but as a scientist, I’d have to say it’s looking like our Universe seems to not be constructed in a very convenient way for humans to get from star to star. And the sci-fi which we end up staying close to our Sun, but we do amazing things with bioengineering or information technology or A.I. seem more likely to be realizable with our physical laws, than Star Trek.