Music and the cosmos
This week Science Show presents a special event celebrating the International Year of Astronomy. The University of Sydney gathered its forces from physics and music for this journey around our galaxy and beyond. Hear how violent, chaotic and dangerous the universe is away from the comforts of planet Earth. When stars like our Sun some to the end of their lives, they explode in a catastrophic event known as a super nova. The last one happened in our galaxy 400 years ago. Some galaxies see them almost monthly! Then there's the search for planets, and the possibility of extra-terrestrial life. So far more than 300 planets have been discovered although so far there's no evidence of life beyond Earth! The evening featured The Sydney Conservatorium Brass Ensemble performing movements from Gustav Holst's The Planets suite.
Robyn Williams: Thank you and welcome. It's of course the International Year of Astronomy and the reason being that we're celebrating the fact that Galileo did his first observations in December 400 years ago. Has anyone here seen Galileo? If you go to Florence, to the museum, you go to one of the floors and you pass a reliquary and there is an index finger and that's Galileo's. How they got it is a strange story.
However, the reason that we're here tonight, quite close to the middle of the year, is that there was another person involved 400 years ago, and that was Thomas Harriot, an Englishman, who got a telescope in July 400 years ago, pointed it at the Moon and made a wonderful representation which you can actually see reproduced in the current edition of Discover magazine. So 400 years ago he did it first, and the reason we don't know that is he didn't publish. Let that be a warning to the scientists; publish or be forgotten!
Mind you, it's also an anniversary of this hall, 150 years, which is wonderful. It's also another anniversary and we're disproving the basis of that anniversary, 50 years ago CP Snow talked about the two cultures, science and art, being separated. Well, we unite them almost as a matter of course. Other anniversaries come in, Apollo I shall mention later, but it's also this week the middle of International Compost Week, which I think is very exciting.
I've been doing The Science Show for some time, and when the program had been on for 30 years back in 2005, Sydney Observatory were kind enough to name a star after me in the constellation Carina. So I was trying to find out what sort of star this is and whether I need to go there to check it out to see whether it's a wimpy star, an average star like our Sun...our Sun is a second generation star, which means it's been formed fairly recently, 4.5, 5 billion years ago. Some of the other ones, the really gigantic ones, formed from hydrogen, were vast things but they didn't last long, only a few thousand years, and exploded hugely. And of course one's watching those sorts of ephemeral events, flashes in the sky, with some of the new telescopes, looking back at about 11 billion years, that first generation of stars.
One of the superstars we have next for you is Bryan Gaensler who is Professor of Physics at the Sydney Institute of Astronomy and ARC federation fellow in the school of physics. He was a former Young Australian of the Year in 1999, and now he's doing some wonderful research. Would you please welcome Bryan Gaensler.
Bryan Gaensler: In a few minutes you're going to hear a performance of Mars, the Bringer of War. As a prelude to that I'm going to spend a bit of time giving a feel for just how violent and chaotic and dangerous the universe is. When we look up at the sky at night and get away from the city lights and see the beautiful night sky, one can often find comfort in that no matter what happens down here, the stars never change. We use the same constellations that were talked about by the Ancient Greeks and Egyptians, and in fact many of our names for the stars and constellations were taken from those ancient peoples. If we choose to turn off our GPS we can navigate by those same stars that sailors used in the age of exploration. And it's quite easy to recognise the same patterns that the first Australians saw above their campfires tens of thousands of years before European settlement.
So, based on this one might come to the conclusion that while cities rise and fall, people live and die, the Earth changes, the stars thankfully never change. But that conclusion is quite erroneous. The universe is a bubbling, seething dynamic place. Just like people, stars are born, they live and they die.
About five billion years from now the Sun will die and it will do so in a rather unspectacular fashion. It will sort of sputter out and then gently puff off its outer layers. However, there are much bigger stars than the Sun, stars that are eight, ten, 50, 100 times more massive than the Sun, and when they die they die with a bang. When these big stars run out of fuel they blow themselves to bits in a cataclysmic detonation known as a supernova. We've seen these happen.
These before and after shots, courtesy of David Malin, were taken just before and after the 23rd February, 1987. If you had been looking at the constellation of Dorado that night, you would have seen with your naked eye a new star suddenly appear. Not actually a new star of course but the end of an old star exploding in a supernova. This star was so bright, this explosion, that you could have walked out of your backyard in Sydney (and that's exactly what I did in February of 1987) and look up at the night sky and you could see with your naked eye a star that was not there the night before. The sky definitely changes.
It's worth bearing in mind that it might not be impressive to see a star with your naked eye, but this thing is 170,000 light years away. Before it blew up it would have been completely undetectable with the naked eye but easy during the explosion. These explosions put out an enormous amount of light and heat. In the one second after the star lights up, an explosion, it gives us more light than its entire life; all those millions of years added together, let go in a second.
Here's another way of putting it. Here is a beautiful image of a galaxy known as NGC 4256 which is about 50 million light years away in the constellation of Virgo. This picture taken in March of 1994 shows a supernova going off 50 million light years away. This one star exploding is actually brighter than this entire galaxy of about half a trillion stars added together. So a supernova is a catastrophic end to a star's life that puts out an unbelievable amount of light.
You might think this is quite spectacular from 50 million light years away, you might think wow, you could imagine what would happen if one of these went off anywhere near us. And indeed it would be quite spectacular. If a supernova went off within a few thousand light years of Earth it would be so bright you'd be able to see it during the day. Even after it had faded from daylight, it would be so bright at night you could read by it, it would cast a shadow. You would notice if a star near us died.
So you might be thinking, well, given that we would notice it, given that you could read by a supernova if one went off near us, I guess nothing like that really happens. And indeed in our lifetimes no supernova had gone off that we know of near the Earth. However, we have a wonderful historical record and indeed if you go back there have been these supernovae occurring near Earth in the distant past.
Here are two records of a very bright supernova which happened in the year 1054. Here is a cave painting made by the Anasazi tribe in New Mexico, and here is a more detailed description from the Chinese records of the Chinese court astronomer, both recording the same event, a new star that suddenly appeared in the constellation of Taurus just under 1,000 years ago. We actually owe a huge debt to these ancient astronomers, particularly to the Chinese astronomers who kept beautifully detailed records centuries or millennia before the telescope and modern astronomy was invented.
So just to give you a feel for the sort of information that is passed down to us by these astronomers, here is a translation of a record of a supernova that happened almost 2,000 years ago. So the astronomer wrote: 'In the Zong Ping reign period of Emperor Ling, second year, tenth lunar month, day 60, a guest star appeared within Nanmen.' This is a beautiful record, this is exactly the sort of information that a modern astronomer would report. They tell us exactly what day it happened and they tell us where it happened. It happened within Nanmen, which is the southern gate. In modern astronomy we call that the Pointers or Alpha and Beta Centauri, right near the Southern Cross. So any good astronomer will tell you, if they see something in the sky, what day it happened on and where it happened, and we have this information passed down to us over almost 2,000 years.
But there's more. The translation continues: 'It was as large as half a mat. It showed the five colours, and was both pleasing and angry. It gradually became smaller and in the sixth lunar month of the year after next it vanished.' This is somewhat more flowery language than we might use in our astrophysical reports today, but this also gives us vital information. If you understand the translation it tells you how bright the supernova was, what colour it was and also quite clearly tells us how long it took to fade away. So this is just the same sort of information we extract from modern supernova and gives us a wealth of information about something that happened almost 2,000 years ago.
It's worth bearing in mind that these ancient astronomers didn't know about how stars worked, they didn't know about supernova explosions, so they really had no idea what this was. They took this as a portent or a warning or an omen and this was the point at which the translation starts to deviate from what you might expect from a modern astronomical analysis. The standard interpretations say this means 'insurrection': 'Wu-kuang attacked and killed Ho-miao, the general of chariots and cavalry, and several thousand people were killed.' Thankfully we don't react this way when we discover supernovae now.
So that's one supernova. We think that on average a supernova happens in our own Milky Way maybe once every 50 or 100 years. As luck would have it we haven't seen a supernova in our own galaxy since the year 1604, and would you believe it the telescope was invented in 1608 and we haven't had one since. But on average we think that in a galaxy like the Milky Way, about once every 50 or 100 years. But there are other galaxies where a supernova isn't occurring once every 100 years but occurring, say, once a month. There are galaxies where supernovae are going off like popcorn, and when this happens you don't just get a local disturbance but the whole galaxy gets disrupted by the effect of all these stars exploding.
And here's a rather nearby example of this. This is a very famous nearby galaxy called Messier 82, it's just in our backyard, it's only 12 million light years away, and it's in the constellation of Ursa Major. Here you see the galaxy but what you can see is that there's hundreds of supernovae going off in the core of this galaxy and the effect of all of these supernovae going off one after the other, just endless series of supernovae, is that the guts of the galaxy are actually being blasted off into space at hundreds of thousands of kilometres per hour. So the effect of these violent supernovae is not just to create a beautiful flash and to blow up one star but to actually start to disrupt the entire structure of the galaxy through the combined effect of explosion after explosion.
Now, you might think that if there are no supernovae anywhere near us, we're probably not going to be affected by supernovae, but that's not true because the Earth is actually under attack from the remnants of supernovae. Supernovae generate small subatomic particles, electrons and cores of atomic nuclei called cosmic rays, and these cosmic rays travel through space at about 99.99999% of the speed of light and fly across the galaxy in all directions, crashing into the Earth. There are hundreds of cosmic rays slamming into the Earth every second. Very few of them reach the ground because they disintegrate into a shower of sparks in the Earth's atmosphere. But indeed it's well known that if you fly a lot in planes you will get a higher radiation dose than if you stay on the ground and the reason for that is because of these cosmic rays that the universe is swarming with thanks to the supernovae that create them.
Cosmic rays actually turn out to be quite important because there's lots of nitrogen in the Earth's atmosphere, and when a cosmic ray smashes into a nitrogen atom it actually converts it to radioactive carbon, carbon 14. We breathe in that carbon 14 carbon and parts of our body have small amounts of radioactive carbon in them, and that allows us to use radio active carbon dating. When you date a tree or a body or a building, you actually use the radioactive carbon that was created by cosmic rays. So there are actually atoms in your body that only exist because of the influence of distant supernovae.
All right, but apart from the explosions, apart from the cosmic rays, surely that's the only trouble that supernovae can create? Wrong. Because after a supernova explodes, it normally doesn't disrupt the entire star but the core of the star is left behind as an extremely violent object. Probably the most bizarre examples of this, arguably the most bizarre stars in the universe, are stars called magnetars, they're very, very strange stars. They're made entirely of neutrons. They're not normal stars made of gas but just made of pure neutrons. They're heavy. They're 1.5 times the mass of the Sun which is about 3,000 trillion trillion tonnes. That's not that remarkable, there are many stars that are heavier than that, but the catch is that a magnetar is only 25 kilometres across. A magnetar is smaller than Sydney but it weighs 3,000 trillion trillion tonnes. So if you compress that much mass into somewhere smaller than Sydney, as you could expect, you have a star that's extremely dense.
If you walked up to a magnetar with a teaspoon, and I should caution that this would be a really bad idea, but if you did and you scooped out one teaspoonful of magnetar material, that one teaspoon would weight the same as 40,000 Sydney Harbour Bridges, crammed into one teaspoon. These are the densest objects in the universe. And they're not only very dense, they're incredibly hot. The surface of a magnetar is millions of degrees. You might think the Sun's pretty hot but the surface of the Sun is only a mere 6,000 degrees Celsius, and that's pretty chilly compared to a magnetar, tens of millions of degrees.
But the kicker, and what's suggested by the name, is that these are also the most magnetic objects in the universe. The magnetism on the surface of a neutron star is 1,000 trillion times stronger than the magnetic field of the Earth. The magnetic field of a magnetar is so intense that if a magnetar was 200,000 kilometres away it could still wipe every credit card on Earth.
So let me tell you what a magnetar did to us just a couple of years ago. At 8.30 in the morning on the 28th December 2004, a rather sleepy time, even for astronomers, after Christmas, a magnetar with a rather poetic name of SGR 1806-20 gave off an unbelievable 0.5-second flash of energy. For half a second this little magnetar only 25 kilometres across was brighter than the 200 or 300 billion stars in the Milky Way combined, and it was not just brighter than the 200 or 300 billion stars in the Milky Way, it was brighter than them by a factor of 1,000. Another way of putting it is that in half a second that flash from this magnetar put out more energy than the Sun puts out in a quarter of a million years.
This flash was so intense that it ionised the Earth's upper atmosphere, and this effect was actually detected by ham radio operators. Even though the magnetar is 50,000 light years away, it sent out a flash that ionised the Earth's upper atmosphere. And we didn't just detect one flash from this magnetar, we detected two. We saw the initial flash and then we saw another weaker flash about two seconds later because the flash travelled past the Earth, bounced off the Moon, and then we got the echo a couple of seconds later. So this was pretty spectacular. We're not used to stars actually affecting us.
So what do we think happened? Well, the crust of a magnetar is under enormous stress because of the intense magnetic fields, and we think that this was the star quake to end all quakes. The star quake fractured the star's crust and released an unbelievable amount of energy in that fraction of a second. The light and heat from this quake was so intense it actually blasted off the mass of a small asteroid off the surface of the magnetar and out into space at about three-quarters of the speed of light.
So this was pretty spectacular. But it was 50,000 light years away and it didn't really affect the Earth. The Earth's ionosphere recovered in a few hours, all of us were perfectly safe because we were protected by the atmosphere, the three astronauts aboard the international space station were above the atmosphere and they got a radiation dose equivalent to about a dental x-ray. So a dental x-ray is pretty amazing when the x-ray machine is 50,000 light years away, but it didn't really affect us in any serious way.
But it's sobering to think what would happen if a supernova explosion or a magnetar quake happened within five or ten light years of Earth. The flash of gamma rays from the explosion would actually completely destroy the ozone layer on the side of the Earth facing this event, and this would let through all the strong ultraviolet light from the Sun for a few years until the ozone layer could repair itself. This bombardment of ultraviolet light would cause all sorts of mutations and radiation damage and extinctions at the bottom of the food chain, species would go extinct, the food pyramid would collapse, and there would be a worldwide catastrophe for both humans and animals.
So I wouldn't add this to your list of things to worry about. On average you would expect a nearby supernova or a star quake from a magnetar maybe once every billion years. But it's interesting to note that about once every billion years or so there is an extinction in the fossil record, and while we think we can explain some of these extinctions (we all know what happened to the dinosaurs), there are other fossil extinctions that we cannot explain. So it's not unreasonable to suggest that one or more extinction events in the Earth's past or indeed some potential future extinctions that we might have to undergo could be caused by a supernova or a magnetar.
So I hope events like this make it clear to you, as they have to me, that we really aren't detached observers gazing at the cosmos. This is not like looking at the microscope and throwing away the slide when you're done, rather we live on a small planet orbiting an ordinary star in a vast, violent galaxy. And our galaxy is one of many trillions of galaxies in the universe. The violent events that the universe puts forth for us make you realise just how insignificant we are in our tiny speck of dust, but they also make it clear how privileged we are, that we tiny dust motes in an unimportant part of the universe can understand the incredible power of the cosmos and our place in it. Thank you very much.
Robyn Williams: Now I'd like to welcome onstage the musicians for tonight, the conductor Scott Kinmont, and the ensemble, the Sydney Conservatorium of Music brass ensemble and percussion, who consist of a total of 16 players, that's five trumpets, four horns, three trombones, two tubas, one baritone, percussion, five timpani, gran casa and other percussion. And of course the first work is Mars, the Bringer of War, part of the suite The Planets by Gustav Holst, who shares something in common with our conductor. Scott Kinmont is one of Australia's leading brass players and has been a lecturer of trombone studies at the Sydney Conservatorium of Music since 2005. And of course Holst turned from piano to the trombone because poor Gustav was not a very well person, so his physical as well as his mental state was often in turmoil, and that's one of the reasons he turned to the trombone.
In fact we're going to hear several parts of the suite. Mars, the Bringer of War doesn't narrate a particular battle, rather the musical events, the chromatic inflections and ramblings, the insistent but unconventional rhythmic figures act as metaphors of the emotive states which we associate with the idea of war. And, when you think of it, this quiet, rather reserved schoolteacher from the West Country who came to London and did most of his work there, who composed it, finishing in 1916 and had its first performance in 1919 conducted by Sir Adrian Boult, he was capable of really surprising some of his audience. He thought himself occasionally to be a failure but others recognise how wonderfully successful he was. Mars, the Bringer of War.
Robyn Williams: Well, there's another anniversary I mentioned right at the beginning and that is of the Apollo missions. It was my delight when I first joined the ABC in 1972 to cover Apollo 16 and 17, that was the last time men walked on the Moon. However, 40 years ago in July, Apollo 11, and of course in November, Apollo 12, which was the really scientific one...on the first Apollo 11 they went to collect rocks and see whether it could be done...it's always a question to think, I often wonder, whether walking on the Moon is an old-fashioned thing to do or not. You certainly couldn't do it at the moment, we don't have the technology, which is something of a surprise.
Which gets me to introduce Tim Bedding, our next speaker, who specialises in high precision observation of stars. Most specifically he researches and is a world leader in astro-seismology, the study of stellar oscillations. Would you please welcome Professor Tim Bedding.
Tim Bedding: Thank you and good evening. I'm going to talk about planets, and we just heard one, we just heard Mars, the Bringer of War. And of course there are nine...sorry, hang on...sorry, there are eight planets in our solar system, but I'm not going to talk about our solar system, I'm going to talk about other ones. It's been of course an age-old question; are we alone? Are there other planets out there around other stars? And eventually of course we'd like to know if there's life on those planets. At the moment we can't answer that question, but the first question—are there other planets?—the answer is yes. And so that's what I'm going to talk about today.
When you have a look at our own solar system you see that it is indeed very varied. We have of course in the middle the Sun, an enormous hot ball of gas, so big and hot that in the middle it has nuclear reactions which create the energy that sustains our life. And then we have these planets out here and we have the big four gas giants, Jupiter, Saturn, Uranus and Neptune, and these are basically balls of gas, enormous things, mini stars themselves but not big enough to have their own fusion. So you might like to call them failed stars.
And then in the middle here we have the small rocky planets like this miserable little lump of rock we're walking around on today. We are quite attached to it, of course, but it is rather a puny little thing. The question we want to ask ourselves is; are there other solar systems like this out there?
The first thing we must realise is there's a very big misleading thing...the sizes of the planets are...and the Sun, the Sun is indeed huge, Jupiter is bigger than all the rest of the planets put together, but even Jupiter has only about 1,000th of the mass of the Sun, so planets are fairly small compared to stars, but they're much, much more spread out. Indeed, on this scale I calculated that you want to spread the whole thing out so that the Earth, for example, would have to go hundreds of metres away. Jupiter would have to go about five kilometres away, somewhere towards Bondi Beach, and Neptune, if this was to be to scale, would be somewhere up on the northern beaches, around Dee Why. So the solar system is indeed huge.
Of course the Earth and all these planets go around the Sun. The Earth takes a year to go round the Sun, and the farther away you go the weaker the gravity and the longer they take. So if we zoom out now and see the outer planets...and Jupiter takes about 12 years to go around the Sun, so that's a long time. If we were to discover Jupiter around another star, we'd obviously have to be very patient. And Neptune, as another good example, takes 165 years to go around the Sun, the gravity out there is so much weaker, and it's about 30 times farther away from the Sun than we are. So from Neptune the Sun is actually not nearly as bright as it is for us.
Okay, the solar system is big but space is even bigger. If we were to go to other stars and ask other planets around them, we have to go much farther. The nearest star to us after Neptune is Alpha Centauri. On the same scale that I talked about you would have to move it not to Dee Why, not even to Perth, but about halfway to the Moon to be on scale. Alpha Centauri is 4.2 light years away, and that's just the closest star. Space is big. If you think it's a long way to the corner store, that's peanuts compared to space, as Douglas Adams wrote.
So here we have many, many stars. Are there planets around them? Of course our star is just one of many in our galaxy. There are more than 200 billion stars in our galaxy, and then spread out across the universe there are more than 100 billion galaxies. So there are a lot of stars out there. So do any of them have planets? Well, now we know the answer is yes, and in fact we know that planets are actually fairly common.
The problem to find planets is that planets compared to stars are small and faint. So if you have a star and you have a planet next to it, the planet is so small and faint it's very hard to see. Here is what I prepared earlier...I'm just going to grab my star from over here. So if this is our star and then next to it we have a relatively large planet, what you have to imagine is this thing is glowing with its own light and is millions of times brighter than this thing, which is merely glowing in reflective light. So you have almost no chance at all of seeing this little guy because this thing is so bright. So we have to resort to indirect methods. This thing is going around its star but because of gravity they're actually both going around each other.
So the wobble method of finding planets around other stars (this is the first of three methods I'm going to talk about) relies on the fact that as the star goes around the planet, the planet goes around the star, they wobble. So the idea is that the star, being nice and bright, is visible. You can measure its wobble, even if you can't see the planet itself. How do we measure this wobble? You might say we just watch the star and see it moving but that's actually quite hard to do. There's actually a much better way, an indirect way of doing it, and that's thanks to this fellow, Christian Doppler and the Doppler effect.
The Doppler effect is quite well known to those of you who've been caught by the police speeding because it's the method they use to measure how fast you're going. The Doppler effect is a measurement of speed, and the way it works is as follows; you have a source of light that's moving and when that source of light is moving towards you the wavelength of light is compressed and the light appears slightly bluer. If you are, on the other hand, over this side and the light source is moving away from you, the wavelength of light is expanded and it appears slightly redder. So if my star is wobbling, then as it wobbles the light from the star will change its wavelength by a very small amount. It's a very, very difficult measurement to make but with new technology in the last decade or two it's been possible to do this.
The Doppler effect also works for sound and it's much easier to demonstrate with sound. The way it was first done by Doppler and his colleagues back in 1842 was to use musicians. So they got the musicians on the train and they got them to play notes as the train went past. So if all the orchestra could stand and run up and down the hall...I'm kidding. So instead I've got this [tone], a very beautiful musical note, and what I'm going to do is swing this around my head, hopefully without killing any of the orchestra. What I want you to listen for is the note; as it comes towards you and goes away from you the pitch should change, it should get slightly higher and slightly lower, so see if you can hear that as I swing it around. [tone] Can you hear it going up and down very slightly? So that's the Doppler effect for sound. But, as I said, what we're interested in is the Doppler effect for light. The Doppler effect for sound can also be demonstrated by swinging a cat [shows film]. I have to assure you no cats were actually hurt in the making of that film.
The first planet to be discovered this way was discovered in 1994, so this is the light, measured velocity, from a planet called 51 Pegasus, and it was measured in 1994 several times by very precise measurements, and this variation up and down in the velocity of the star is the wobble that betrays planets around it. If you take all those measurements which were taken at different times and you line them up you get this, and you can see there's a really nice up and down motion.
This was an incredible surprise at the time. These people were looking for planets but they weren't expecting to find a planet like this because what I haven't told you is how long it takes; 4.2 days. This is a planet that is orbiting its star much closer even than Mercury, and yet it's a big planet. This is a planet as big as or bigger than Jupiter and yet it's in a very, very close orbit. Nobody was expecting to find this, it was a complete surprise, which shows you in science that when you go out looking for something you must always be on the lookout.
In fact there was another group in America who'd observed the same star but because they weren't expecting to find a planet after only a few months, they hadn't actually got around to looking at their data carefully. When this was published they looked at their data and they saw the planet too. So that goes to show that you shouldn't have too many expectations.
So this was the first of such planets to be found, these planets that are very close in to their star, and they were nicknamed 'hot Jupiters' because they're bigger than Jupiter but they're very close in, which makes them very hot. We don't have any pictures of hot Jupiters but we have artists, and so the artists have got busy and made some artists' impressions of what they might look like, and you can scour the internet and find lots of pretty pictures. This is one of the things that I think sometimes annoys scientists is that when you turn on the news and you see these stories, they intersperse these pictures with the real ones and it's very hard to know which one is which.
These are not the only sort of planets that have been discovered. There are some other planets with much longer periods. Here's one called 47 Ursae Majoris, and this time on the bottom is time in years going all the way back to 1990. You can see that this planet has a period of a couple of years, so it's farther out. In fact, it's not just one planet here, there are actually two. You can see it's a fairly complicated signal, not just going up and down, and so this was the first time it was discovered that there was another solar system, not just one planet in it but two.
And so this method has been used so far to find most of the planets to date, but there is a second method that I want to talk about and that's the transit method. You probably all know what a transit is because you probably saw one back in 2004, Venus traversing the Sun, taking several hours to do so, the transit of Venus in 2004, a very exciting event. But if you imagine that this was a star that was very distant, of course you couldn't see that, it would be too small to see. The stars in our galaxy are presumably being orbited by planets in random directions, and so at least some of the time we should get lucky and see a transit.
We don't have enough resolution to image the little spot moving across the disc, but instead what we can do is measure the dip in the light. So we measure the total amount of light coming from the star. As the transit happens we measure the brightness and for a few hours the brightness goes down. It's a small effect but it will repeat at regular intervals every time the planet goes around the star.
You remember our hot Jupiters, they go around their stars every few days, four, five, six, seven days, and there have been lots of them discovered now. They've all been looked at, and occasionally if you're lucky you might see a transit if the system happens to be edge-on. And indeed that happened. The first one was discovered in 1999, two transits on two different days. These were made from the ground, but if you go into space and use the Hubble space telescope, as they subsequently did, you find much more accurate observations.
Why is it so much better from space? The reason is you're above the Earth's atmosphere. That makes the stars twinkle, which is very pretty if you're a poet, twinkling stars and all that, but it's very annoying for the astronomers. The twinkling of the stars really makes our measurements very difficult. So going into space allows much more accurate measurements.
Since that time there have been lots and lots of attempts to measure planets, and there are lots of search programs going on around the world, and they're using quite small telescopes. So the advantage of the transit method as opposed to the first method, the Doppler method, is that you can look at lots of stars at once this way. The velocity method with the Doppler shift you have to do one star after another quite painstakingly. So the transit search programs have managed to discover now quite a few planets and that number will go up.
NASA launched a mission in March called Kepler, and Kepler is a space telescope specifically dedicated to finding planets around other stars. A big spectacular launch, the rocket is up there now, they've opened the lid, they've taken some pictures, and the thing is there and better still the thing is in focus (for those of you who remember the Hubble space telescope debacle). Each one of those little tiny dots in there is a star. Those stars are re-monitored continuously for four or five years looking for the tiny dips that happen as the planets go in front of their parent star. Most of them won't show anything, but a handful of them, maybe a few hundred, will show dips, even as small as dips from the Earth.
You see, so far the planets that have been discovered haven't been as small as the Earth. Jupiter, maybe a bit smaller, maybe down to Neptune mass, maybe sub-Saturn mass, maybe down to a few Earth masses, but the technique for discovering Earth-size planets requires much more sophisticated and sensitive measurements because the Earth is so small. But it's one thing to discover a big planet transiting a star, it's much harder to discover a small planet. So this is the first mission that will be capable of detecting Earth-size planets, and we hope that in the next few years that will happen. Indeed our group here at the university is working with NASA and has access to some of the data that we'll be analysing. So that's an extremely exciting mission.
So finally I want to come to the third method that you can use to detect planets, and this you might think is the most exciting, this is to see them directly. Direct imaging of planets, as I said to you at the beginning, is very hard because the star is so bright. You have this really bright star and this faint thing next to it. But if they're far enough apart it may be possible, and it's been done twice so far.
This one here, which made quite a splash a few months ago in the press, this is a picture of a bright star called Fomalhaut. So this is the first direct image of a planet around another star, but it's not like our planets. For a start it's so much farther out, many times farther even than Neptune. And in order for us to see it at all it must be quite big, it must be many times the size of Jupiter. So that's the first one that was discovered, and the second one is this star here. This has two planets around it. This is a star called HR 8799, a very exciting name but a very exciting star too. So this is an observation that was made in 2007 and in 2004, very difficult observations and that's why it's so tough. And, again, this one is a fair way out. A third image was made with the Hubble space telescope and over the time that this thing has been discovered from 1998 through to 2008 this planet has moved around in its orbit. So this is a solar system but not like our own at all.
Okay, so how many planets? Do you want to know numbers? So far, according to the internet this morning, 347 planets have been discovered, and it's probably changed by now. Not all of them are single systems, 37 are solar systems with multiple two or three or even four planets around them. How were they found? Most were found using the Doppler wobble method, some were found using transit searches, only a few using direct images, but now with the launch of the Kepler mission this number will go up. Transit searches will start to produce more and more and more planets.
What do we learn from them? What can we conclude from all this? There are two things. One is that planets are quite common. Around about 10% of stars seem to have planets around them. But those solar systems are very different from our own. The orbits of the planets and the planets themselves come in a huge range of sizes and that shows us that the universe out there is very different from our own. We may one day discover a solar system like ours but at the moment we're finding things that are extremely different.
That leads me to the final point I want to make, and that is when you go out looking for stuff, you hardly ever find what you expect. The universe is stranger than we can possibly imagine. And so just like Bryan I managed to find a Shakespeare quote for the occasion, and there it is: 'There are more things in heaven and earth, Horatio, than are dreamt off in your philosophy.' Thank you very much.
Robyn Williams: Thank you Professor Tim Bedding. And, by the way, you were talking about the solar system in terms of geography...if you actually go to Gingin in Western Australia to the Gingin Observatory, which is about one hour outside Perth, you can walk the solar system and get a true idea of the amazing distances between the outer planets. It's an interesting thing to do and takes quite some time actually. It's worth it. They've got pottery planets, which is rather good fun.
We've been rejoined by the conductor Scott Kinmont and we're about to hear the fifth in the series of The Planets and this one is Saturn, the Bringer of Old Age.
David Fisher: Now for some questions from the audience. Our astronomers are joined by Professor Geraint Lewis. We'll hear his full address next week.
Robyn Williams: Tim, the question Fred Watson comes out with; why is Uranus called 'upside-down'?
Tim Bedding: The planets all spin, the Earth spins around on its axis, that's why we have night and day, and the Earth's axis is almost vertical in the solar system, it's tilted about 20-something degrees. All the other planets are the same except for, for some reason, Uranus, which is spinning not upside-down but pretty well on its side. It's probably that in the early solar system it was hit by something that knocked it off its axis. But it's not quite horizontal, it's actually spinning slightly below horizontal, and that's why Fred Watson likes to say that Uranus is upside-down.
Question: Hello. Is there a planet out there which is capable of sustaining or starting life?
Robyn Williams: We might need it.
Tim Bedding: Yes. If you mean by 'sustaining life' having liquid water, which is what most people think of when they talk about sustaining life, the answer is probably there is one or two so far. Most of the planets are either too close to their stars, the very hot ones, so there could be no liquid water, or too far away. But there are regions (some people call it the Goldilocks Zone) where liquid water can exist. So far there have been about two planets that are probably in that zone. So the answer is yes, but whether they have life of course is a very long way to go.
Robyn Williams: But Tim, if we've got ten billion stars in our galaxy alone, maybe 100 billion planets, surely a couple of them..?
Tim Bedding: You'd think so, wouldn't you. The great Carl Sagan was often asked this question and he was always being pushed, 'Do you think there's life out there?' And he'd say, 'I'm not sure.' And then they said, 'So what's your gut feeling?' He said, 'I try not to think with my gut.'
Robyn Williams: A question over there please.
Question: Yes, that was actually my question. Presumably there are specific numbers you can speculate about the number of planets there are in our galaxy, and then if you can speculate on that then presumably the timescale of the evolution of planets and therefore the timescale of life. So there should be somebody sitting in a hall not dissimilar to this one in about four or five planets somewhere, say, right now. Have you thought about that?
Tim Bedding: My main problem with all of this is all we know is us, and that's the only example of life we have. So it's almost arrogant to think that life out there would be anything like life on Earth. The one thing we learn when we explore the universe is, and as I said in my talk, that it's stranger than we ever could imagine. So I think it's just too far away to speculate what possible life would even look like out there.
Robyn Williams: Bryan, do you want to speculate?
Bryan Gaensler: The galaxy is a very big place. Even if there are, say, three or four planets like us right now in our galaxy, there are tens or hundred thousand light years apart. So just to know that they're there and to have a conversation with them, you say, 'Hello', you wait 50,000 years, they say, 'Hi, how are you?' another 50,000 years, 'Good thanks.' It would be very hard to be able to learn much about them. In particular, our modern civilisation as we know it has only been around for a few hundred years and we've only known about planets and other stars for ten years. Can our civilisation remain in a state which is capable of communication for 50,000 or 100,000 years? I don't think that's clear. So maybe civilisations don't hang around long enough to be able to let anybody else know that they're there. That's a big unknown question.
Robyn Williams: Yes, the one thing that has always really bamboozled me about this is if Radio National had been there for the Sermon on the Mount 2,000 years ago and broadcast it at the speed of light, it would have travelled just a tiny amount through our own galaxy, let alone beyond it. The distances are unbelievable. Yes, there's a question just down here.
Question: Maybe I should already know the answer, but what is the definition of the environment before the Big Bang started?
Geraint Lewis: That's easy; we don't have a clue. As astronomers we can explain using the laws of physics and science as we know it from a fraction of a second from the Big Bang to today, it all works really well. You've got the Large Hadron Collider in Switzerland which is recreating the conditions which were just after the birth of the universe, it all agrees with that, the physics that we understand. That little bit before, getting back to the Big Bang, is currently beyond our scientific means. We just do not have the scientific knowledge to tackle that problem. I don't know if it will be ten years, I don't know if it will be 50 years, but there will be a time where we will know how to push that boundary further. There are speculations on how to do it but we don't have the robust ideas yet.
Robyn Williams: There was a restaurant there before the beginning of the universe.
Question: What would happen if two stars did hit, when two galaxies collided?
Geraint Lewis: Oh, fireworks. It would be spectacular. You crash two stars together they've got these furnaces at their hearts, these nuclear furnaces burning away. If you smash them together hard enough you can rip the star open and all that energy just gets spat out in an instant. You effectively turn off the reactor but it's a huge kaboom and then blackness. It would be pretty cool.
Bryan Gaensler: I should add that there are these tiny balls of stars called globular clusters where you pack about a million stars into a ball that's only a light year or two across, and the stars are all furiously orbiting each other, and it's just a very different environment from our neighbourhood and where the stars are very tightly packed. In globular clusters we think that occasionally stars do smash into each other and you get these very exotic objects called blue stragglers and Thorne-Zytkow objects. We don't actually see the dramatic collision but we see these very bizarre stars left behind that look like the equivalent of the head of a donkey and the body of a lion and the tail of a snake because you've taken two different stars and you've mixed them together. So we think that does happen under special conditions.
Question: My question is if the star is too hot and the planet goes right next to it, wouldn't the planet melt?
Tim Bedding: If the planet is too close to a star would it melt? Well, it would evaporate perhaps. If you took Jupiter and put it right near the Sun, indeed that is a problem for the theoretical models because some of these hot Jupiters really would be extremely hot. But the calculations that have been done so far indicate that they can survive. They weren't formed there however. So Jupiter was formed out where it is, about five astronomical units from the Sun. These hot Jupiters were probably also formed out there, but in the early system of their solar system there was so much debris left around that essentially by friction they spiralled their way in and rather than being gobbled up they stopped just short. So as long as they're not too close to their parent star they can survive. They'd be pretty hot on the side facing the sun, and some of the material would evaporate but they could indeed survive.
Question: It's a basic question but I'm just a little bit confused with Pluto being knocked off the list of planets. What does define a planet?
Tim Bedding: Oh, what time is it?
Bryan Gaensler: Let it go, people! Pluto is gone!
Tim Bedding: I was there. Where you guys there? Three years ago there was the big conference, we were all talking about lots of astronomy, galaxies, planets, and then there was a meeting, a room like this, and we had to make the decision. They've discovered new stuff out there. There are objects farther out than Pluto, similar to Pluto, one even bigger than Pluto. So do we start adding more and more planets to the list, do we call them planets, or do we say, well, actually Pluto probably shouldn't have been called a planet in the first place, it's not really very big? And so the decision was made to cut the list at eight. The other guys, they're interesting, they're fascinating objects, but we won't call them planets. The definition of a planet now is slightly complicated but the object has to be big enough that its own gravity makes it round. Pluto does pass that test, but it also has to be big enough that it dominates its own orbit, and Pluto is not that. Pluto is in fact locked in an orbit with Neptune and is tugged around where Neptune wants it to go. So Pluto is not big enough to be called a planet, and I'm afraid that decision is not going to be reversed.
Question: Tim, which way did you vote?
Tim Bedding: I voted the way that it turned out, I have to say. My children have yet to forgive me but hopefully one day they will.
Robyn Williams: My question to all three of you, starting with Tim; Sir Martin Rees or Lord Rees the Astronomer Royal said to me once that he'd be willing to take a one-way ticket to Mars. Getting back is so difficult he'd be willing to go if it's one way. Tim, would you?
Tim Bedding: No, I wouldn't. I would love to go and it would be fantastic to see it but I don't think it's worth a one-way ticket.
Robyn Williams: Geraint?
Geraint Lewis: No. Not with my wife and kids sitting in the second row anyway.
Robyn Williams: Bryan, you've got a young family...
Bryan Gaensler: I get carsick.
Geraint Lewis: I think there's a good reason why astronauts are young army kind of people who haven't settled down with families yet. If you asked me 20 years ago I may have had a different viewpoint.
Robyn Williams: There you heard speakers Bryan Gaensler, Tim Bedding and Geraint Lewis, all professors of physics at the University of Sydney.
- Bryan Gaensler
- Professor of Physics
Institute for Astronomy
School of Physics
The University of Sydney
- Tim Bedding
- Professor of Astrophysicist
Institute for Astronomy
School of Physics
The University of Sydney
- Geraint Lewis
- Institute for Astronomy
School of Physics
The University of Sydney
- Robyn Williams
- David Fisher