Radio Astronomy

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Transcript

Tim (00:00): So what Jodrell Bank's been all about, for more than 60 years now, is exploring the invisible Universe.

Tim (00:16): When you go out at night, and you look up at the sky, you're using your eyes to look at what's there. You'll see stars, you'll see the Moon maybe; if you're lucky you might see something like a comet. And for thousands of years, that's what we were limited to doing - just using our eyes. About 400 years ago Galileo first used a telescope, and what the telescope does is it lets us get an enhanced view of things out there in space. So it collects more light, lets us see fainter things, magnifies the view. But visible light - the sort of stuff that your eyes can see - is not the only sort of information that's coming from space. It's only one part of a huge, wide spectrum that goes all the way from radio waves at one end, through infrared, then the visible, and then out beyond that you've got ultraviolet, X-rays and gamma-rays. And, these days, astronomers use every bit of that spectrum to obtain different information about the Universe. And the first bit of that spectrum to be opened up outside the visible - to allow us to look at the invisible Universe - was the radio part of the spectrum.

Tim (01:15): Radio waves are what's called electromagnetic radiation. They're part of this big, wide electromagnetic spectrum from radio waves at one end to gamma-rays at the other, and visible light in the middle. The difference between these different types of radiation is the wavelength. These waves are actually made up of electric and magnetic fields that vary, and the distance between the peaks in these fields is called the wavelength. The wavelength of visible light is very small - it's maybe a millionth of a metre or so. But the wavelength of radio waves is much longer - maybe a few centimetres, or even a few metres. So it's the wavelength that is the crucial difference between radio waves and visible light.

Tim (01:59): Radio astronomy actually began back in the 1930s. Karl Jansky, who was an American engineer, was studying radio waves as part of a task involving using radio waves for terrestrial communication. But he found a source of radio noise that he realised was actually coming from space. So he was the first person to pick up radio waves coming from outer space. Another American called Grote Reber, later in the 1930s, built his own little radio telescope - in his back garden, actually - and he was the first person to start to map the radio sky. Here at Jodrell Bank, observations began in late 1945, so we were some of the first pioneers of the new science of radio astronomy.

Tim (02:42): Here at Jodrell Bank there's actually four radio telescopes. The big Lovell Telescope is 76 metres in diameter. When it was built it was the world's largest radio telescope - it's still the third-largest steerable telescope. There's another large telescope on this site called the Mark II telescope, and together these two work as part of a network of telescopes across the UK - we call it MERLIN - which actually combines five remote telescopes with the two large ones here. This acts as a giant telescope spanning the whole width of the UK - it gives us a magnified view of what's up there in space, a sort of zoom lens if you like, lets us look at details. And then there's another two smaller telescopes here at Jodrell Bank. One spends its life looking at pulsars - the dead remnants of exploded stars. They're ridiculously extreme objects that weigh about as much as the Sun, but they're only about the size of a city. And they spin, in some cases, hundreds of times a second. The other small telescope here is used for teaching, where we look at hydrogen atoms, largely in our own Galaxy. We can measure the spiral structure of our own Milky Way Galaxy using that telescope.

Tim (03:52): The main problem we have operating radio telescopes is the wind. If the wind gets up, and a big dish is tipped over and the wind blows into that dish, then you actually could risk blowing the whole thing down, which you wouldn't want to do! So we have to monitor the wind speed, and if the wind gets up you have to tip the telescope - point it straight upwards, park it, and that's the most stable position. The other issue would be maintenance, in the sense that radio telescopes can be used 24 hours a day. We can observe during the day, we can observe during the night - in principle, if it's not extremely windy, you could use it all the time throughout the year. Pretty soon, it would start to break down. So we do have to factor in periods of maintenance where we look at the structure, we do essential jobs like painting work and so on.

Tim (04:39): The major discoveries that we've made here with the radio telescopes - well, one of the first things we found were what we call 'radio stars', really bright radio sources. And it turned out that many of them, when you pointed an optical telescope in that direction, and you thought, "Well, what are looking at here? Is it a star, is it a galaxy, is it a planet?" - well, there was nothing obvious there in an optical view. And it took some time before the nature of these things was really worked out. Here at Jodrell Bank we pioneered a technique of taking radio telescopes, moving them farther and farther away from the big telescope here, but combining the signals from the two using radio links. So we actually sent the radio signal from the remote telescope back to Jodrell Bank. And, by moving them farther and farther apart, we actually zoomed in, in more and more detail, and we were able to show that these objects were incredibly tiny. As it turns out, these things were what became known as the quasars - the distant galaxies with supermassive black holes.

Tim (05:39): Another major area of work here has been pulsars. They were first discovered by Jocelyn Bell with a radio telescope at Cambridge in 1967. They were first discovered as a repeating radio signal. A spinning neutron star rotates, it flashes, much like a lighthouse, and so you get this repeating, very periodic, flashing, pulsating signal, hence the name 'pulsar'. When they were first discovered, there was a slight concern that actually we'd discovered signals from extraterrestrials. So the first one was called 'LGM-1': Little Green Man 1. Pretty quickly it was realised that they weren't aliens, they were dead remnants of exploded stars, and the Lovell Telescope here turned out to be ideal for studying them. So that's been a major area of work here ever since. We've discovered many hundreds of pulsars, including, recently, a double pulsar - two pulsars orbiting one another. It's actually provided us with the best-ever test of Einstein's theory of gravity, general relativity, showing that Einstein's at least 99.95% correct! We're hoping at some point to prove him wrong.

Tim (06:56): Another major discovery were things called gravitational lenses. This is an effect that was predicted by Einstein with his theory of gravity, where light is actually bent around massive objects. The mass of an object curves space-time, and that means that light gets bent around it. The way a gravitational lens works is that, when we look out at, say, a distant quasar, and in between us and the quasar there's a galaxy - a source of mass - then the light from that quasar is bent around it. And you can get multiple images of that distant object. Much the same way as if you look through your bathroom window (which has got rippled glass) you'll see distorted images of things out in the garden, we see distorted images of things out in space by the mass that's curving space-time in between us and the distant object. Gravitational lenses were discovered in 1979.

Tim (07:51): And perhaps one of the most fundamental things that comes out of radio astronomy is the fading glow of the Big Bang. We believe that the Universe began about 14 billion years ago, in the Big Bang, and it's been expanding ever since - galaxies are flying farther and farther away from each other. But when we look out into space, the farther away we look in space the farther back in time we can see. And the most distant light, and therefore the oldest light, we can ever see is something called the cosmic microwave background. It's light that set off in the Universe just a few hundred thousand years after the Universe began, and it's been travelling through the Universe ever since. But when it set off the Universe was at a temperature of about 3000 degrees, and so it was glowing a dull orangey-red. The Universe has expanded by about a factor of a thousand since then, and so these light waves were stretched to longer and longer wavelengths, until now they're in the microwave-radio part of the spectrum. And so we can use radio receivers - on radio telescopes, or on board spacecraft like the Planck spacecraft - and we can study this fading glow of the Big Bang and look right back in time, right to very near the beginning of the Universe itself, and actually study the origins of stars, galaxies and, in fact, ourselves.

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