The sounds of space


Even though we all love those stunning images of the dark side of the Moon or colourful nebulae or rotating galaxies, astronomy and cosmology are not all about what we can see. More and more astronomers are turning off their telescopes and opening their ears.

Researchers are increasingly paying attention to the noises made by objects in the universe, or how physical laws can shape sound in ways that, to us Earthlings, seem peculiar. Adam Smith meets the scientists who are listening in to the sounds of the stars and calculating how we’d sound on other worlds.

Adam Smith: You’re on a starship that can detect vibrations made by the giant burning balls of gas in space, or stars. And as you stand on the bridge of the ship, this is what you hear…

Dr Roberto Trotta: Light, as important as it is, and vision, is one messenger among many. So it’s important to listen in to the universe in a more direct human scale way will give the public or us as astronomers as well a more human perspective to these incredible distances, incredible scales and timescales and energies that are almost unimaginable in fact.

AS: Elsewhere in the universe, if you land on a planet that’s not Earth your voice will sound different due to the atmospheric and gravitational conditions. Your voice might go from this…

Rhys: My name’s Rhys.

AS: To this…

Rhys: My name’s Rhys…

AS: You see, even though we all love those stunning images of the dark side of the Moon or colourful nebulae or rotating galaxies, astronomy and cosmology are not all about what we can see… Now, more and more space explorers are turning off their telescopes and opening their ears – paying attention to the noises made by objects in the universe, or how physical laws can shape sound in ways that, to us Earthlings, seem peculiar…  I’m Adam Smith, welcome to Pod Academy. Let’s go back to that strange and definitely unearthly sound we heard at the top.

Sound clip

Professor Don Kurtz: That’s an old favourite of mine.

 AS: This is Professor Don Kurtz, who’s spent decades listening in to the stars

DK: When I was a young astronomer, I’m not so young now – you can’t hear that on the radio, I’m 63, when I was a young astronomer I was working at a very remote observatory in South Africa.

 AS: It was there that Don made a startling find. He was looking at peculiar stars – that’s what the astronomers call them – and this is what they sound like again…

Sound clip

….Definitely peculiar. But in astronomer’s terms, ‘peculiar’ means that although most stars are made of hydrogen and helium, when you look at the light of peculiar stars, the elements that are so obvious are rare earth elements such as neodymium, lanthanum – they can be overabundant by as many as a million times in these stars compared to our sun. Don was studying why this class of star is so peculiar… But how on Earth do astronomers like Don do this? If I were floating around in space, I know I wouldn’t hear anything – in space, no one can hear you scream, right? it’s a vacuum, so it can’t carry sound waves.

So astronomers like Don can’t actually hear the stars, but they can observe the vibrations they make and use a computer to study what that says about them. For fun, they can even treat those vibrations as if they were made by a musical instrument – and boost them so that we can all listen in.

DK: Adam, imagine that you get on the telephone and you call your mom. And you say, hi Mom, and you hear her say to you, hey kid. Now is that really her voice that comes out of the telephone?

AS: I guess.

DK: Well, it sounds like her, doesn’t it?

AS: It does sound like her.

DK: But the sound from her voicebox has not come to you. What’s happened is that the sound that she has spoken into the telephone have been electronically analysed and turned into microwaves which are very long wavelength light, and that microwave signal has been transmitted to a tower, which has then retransmitted to your telephone, carrying the information to re-create her voice and then we use that to drive a speaker in your phone and out of your phone comes her voice.

I do a similar sort of thing with the stars. Sound cannot get out of the stars. Stars are very noisy places, full of sounds and many of them have go rather musical sounds in them. But those sounds are trapped, sound can’t travel in a vacuum. So what I do is I watch those sounds cause the stars to vibrate – I can see them getting brighter and dimmer. I can see them coming towards me and going away from me as they swell and contract using something called the Doppler effect. And from that I can find the frequencies, the amplitudes – how loud the sounds are – and the phases, when the stars start. All the information you need to re-create the sound, and if I want to, to recreate them in a listenable form here on Earth. But please note that the sounds are far too deep for us to hear, they’re outside the range of our hearing. So some processing is needed to bring them up to where you can just listen to them for fun.

Sound clip 

AS: Tell us about that one.

DK: That is the pulsating sounds of a red giant star. Red giants are later stages in the lives of stars. Now, we know right now that the sun is growing larger and will eventually grow to be a red giant, that’s the future of our own sun in our solar system.

Yet it’s a mystery at the moment. We calculate that the Sun around 1 billion years ago was about 15% fainter than it is now. If the Sun were to be 15% fainter now we would live on snowball Earth, we would be ice right down to the equator. And yet 3 billion years ago there’s strong evidence in the geological record, from fossils, that we had tropical temperatures. How is it that the early Earth was so warm when we had such a faint sun?

We think we know the answer to that – the partial answer is that at least there was a lot more carbon dioxide and methane in the atmosphere. They’re greenhouse gases and they trapped heat from that faint sun. But we would also like to know what the future of the Sun is, and ultimately the future of the Earth, billions of years in the future. So to do that we need to understand red giant stars. And that star you were just listening to, Xi Hydrae, pulsates with many frequencies with periods of a couple of hours and those have been boosted into the audible to give you that thump-ada-dump-ada-thump-ada-dump-ada sound of a red giant.

AS: As Don implies, there’s music in them there stars. And it’s music that’s not lost on musicians. A couple of years ago in France, musician Eddie Ladoire collaborated with theoretical physicist Jean-Philippe Uzan on a rather unique project. They played about with images of the universe and produced sounds for various cosmological objects…

The project is called Vostok, after ‘Vostok 1′, the capsule in which cosmonaut Yuri Gagarin became the first man in space in April 1961. Sonic space adventurers sit in a special booth and listen to Ladoire’s 20-minute composition which supposedly places them inside a galaxy. Vostok is a sonic experience – the bass at certain points is so deep that you can feel it vibrating your bones.

Roberto Trotta is the man trying to bring Vostok – the music and the special cabin – all the lightyears from France to London. That’s because cosmologist Roberto is this year producing a series of public lectures in the Astrophysics Department at Imperial College London about how all five of our senses can help us to experience the universe. To coincide with the lecture about sound, he’s searching for funds to ship Vostok over. I went to meet Roberto to hear more about the plans and his own research…

RT: We very much hope to find funding to bring this project to London to put it on display here at Imperial College but also the Science Museum, to give as many people as possible the chance to experience this project first hand. What this does is take these astronomical scales and bringing them down in a sound box and giving you a full immersion, a first-hand experience what it is like to be part of an audible cosmos, as it were.

AS: Roberto is not just an art curator. He’s also a working cosmologist, sitting in an office in the Blackett Laboratory at Imperial. Roberto’s office is on the tenth floor, and it has a huge window. With such an expansive view of the sky, Roberto ponders the big questions.

Roberto studies the dark side of the universe – specifically, the dark matter and dark energy that make up 95% of what’s out there.

RT: If you cannot hear them directly in space but you can certainly visualise their acoustic impact as it were in many different ways, that’s one of the prime tools that we use in doing what we call precision cosmology, namely trying to determine quantities that characterise our universe. And sound, cosmic sound, is one of the tools to this end.

AS: So how do you go about actually making those measurements and hearing the sound in space?

RT:  Space is a very silent place to begin with, whenever you hear the spaceships swooshing by on TV you’re sure that the science consultant didn’t do a good job, or else the studio bosses decided that that’s what the public wants to hear and just put it in. So you don’t have sound in space because there’s no atmosphere. However, the universe was not always the way it is today and specifically when we go to the far back of the universe, to just the beginning of time, right after the Big Bang, the universe was a much hotter, smaller, denser place which was filled with dense plasma made of particles of light, and hot matter. And so it was a very hot and dense environment could and did actually propagate. So the sound waves of the Big Bang reverberated in the early universe and nowadays we can pick up the faint echo of this bang with our telescopes and instruments, that is how we go about listening in to the universe.

AS: So you can still hear the echoes of the Big Bang, How many years ago?

RT: 13.7 billion years ago.

AS: That’s a big echo.

RT: Yeah, and it’s quite impressive actually that thanks to these observations we can nowadays actually measure the age of the universe with the precision of about 1%. Now, to put this into context, we know that the Earth is about 5 billion years old give or take, but the age of the Earth is not known with the same accuracy as the universe. And that’s astonishing because we sit on the Earth, it’s all around us, it’s a piece of rock right under our feet! And yet we can investigate and learn about the age of the universe with much more precision and accuracy than we can about the age of the Earth, so it’s a great achievement in cosmology.

AS: Can you explain a little more about how you go about making those measurements? What are the tools that you use?

RT: So first of all we have to be able to pick up this very faint, very cold light that comes to us from the very early stages of the universe, this is light that has been travelling to us for 13.7 billion years, from an age where the universe was about a thousandth of its current size. And when it was about 3,000 degrees hot, so very hot universe with no galaxies in it. And with sound waves propagating through the universe and colliding and so what we do is, we need to have special telescopes that are able to pick up this faint radiation. Now in the microwave wavelength, which means it’s the same kind of radiation that heats up your food in the [microwave] oven, only this one comes from the Big Bang. So we have special telescopes and satellites made that are not your usual telescopes. They don’t have mirrors; they have horns and antennas.

AS: Horns and antennas?

RT: Yes, they are microwave receivers that are used to pick up, not very much the direct radiation but what they pick up is the difference in the temperature of that radiation in different parts of the sky. It’s a map of the universe that you can see on that shelf over there.

AS: The inflatable globe over there?

 RT: Exactly. It looks like a little bit of an abstract painting with blue and red dots on it. But actually it’s a map of the end of the universe.

AS: The end of the universe?

RT: The end of the visible universe. Precisely. It’s essentially as far away as we can possibly see using this type of light. Before then the universe was opaque and was therefore like driving in the fog, you can’t see very far at all.

So that is in fact a map of the end of the universe, and that map in fact, the little blue and red spots that you can see represent temperature differences in this radio antenna and they also represent the crests and troughs of those primordial sound waves super-imposed in a semi-random fashion in a way. If you look at this map, you wouldn’t be able to tell that there are sound waves in it. You don’t see nice spherical shapes. You don’t see crests and troughs but it’s a little like if you take one small pebble and you throw it in a pond you will see nice waves spreading out. But if you throw ten thousand million pebbles, all of them will throw out their own waves but by the time they’re all super-imposed you get this messy, wavy structure that doesn’t show a specific soundwave, but that’s the same as we see here in the early universe, we see the seeds of galaxies.

Each one of them has its own spherical wave going out, there were million and billions of them, they’re all super-imposed and they all travel through the empty universe to us, to give us a map that doesn’t look like a spherical wave any more but if you analyse it statistically you can still tease out the statistical signature of those sound waves.

AS: So you have to do lots of calculations to see these things, slash hear these things?

RT: That’s right, yeah exactly. You have to elaborate this map in a statistical numerical wave and if you do you end up with a very a nice wavy looking graph, which actually is a graphical representation of those sound waves, that really look like a wave, which shows really the reflection in a statistical sense of those acoustic waves in the early universe. So we do call certain parts of this graph the acoustic peaks for the very good reason that they represent the average properties of the sound wave in the early universe.

AS: Is it possible to convert that very nice wavy graph into some music or would that be missing the point?

RT: No, I think that’s a very valuable thing to do. I’ve certainly heard different prescriptions for how you would convert this. Of course, there’s not a one to one correspondence between those sound waves and audible sound. The wavelength of those waves is about a hundred megaparsecs, so now I need to convert this into more daily units…

AS: How many swimming pools?

RT: Swimming pools is going to be hard, but I can say that it’s about 300 million light years in size, there’s about 900 million billion kilometers so you do the maths in terms of number of swimming pools. It’s a hell of a lot of swimming pools to be honest. So this is the kind of size the wavelength of those sounds, so it’s truly cosmological in size.

Those were waves that were propagating in the third of the speed of light in the early universe. So give the light 380,000 years to propagate and then stretch it some more because of the expansion of the universe and that will give you the soundwaves. So those are very big sound waves. But from the graph that we’re discussing, you can find prescriptions how to convert those into audible sound and I’ve heard a few of them. Various people have tried, it’s a very nice thing to do because it really bridges the gap. It brings it back from a cosmological scale to a human scale, which is very nice. So I think it’s a very valuable thing to do.

AS: And when we think of astronomy as members of the public, we do think of those stunning images that telescopes like Hubble collect, we don’t really think about the sounds so much. Do you think that should change?

RT: Definitely, it should change because light, as important as it is, and vision, gives us a one-dimensional perspective on the universe in many ways. It’s one messenger among many. So having the opportunity to listen in to the universe in a more direct human-scale way will give the public or us as astronomers as well a different perspective, a more human connection to these incredible distances, incredible scales and timescales and energies that are almost unimaginable in fact.

So I really think that bringing it down to a more experiential level via sound and via the conversion of those images into meaningful sound patterns, that’s a very valuable thing to do because it brings us more in direct connection and it enlarges our horizon because it gives us a more immersive experience. Why just limit ourselves to just one of our five senses? We should definitely try and use them as much as we can. All of them.

AS: Why limit ourselves, indeed? In fact, let’s not settle for listening in to the universe – let’s get out there ourselves!

Now, when we get out into space and eventually travel to other planets, we’ll have to think about where we’ll live, where we’ll spend a penny, whether there’ll be a decent takeaway – loads of mission-critical things. But have you ever thought how you’d sound on another planet?

The different degrees of gravity and the compositions of the atmosphere on other worlds is going to be different to Earth. They’ll change your voice entirely. So when you phone home to your mum during your voyage to Venus, she might not even realise it’s you.

Professor Timothy Leighton: The first thing is that our vocal cords slow down. The atmosphere on Venus is many times thicker than the atmosphere here, so the vocal cords instead of fluttering lightly in Earth’s atmosphere, they have to really ponderously slave away, vibrating up and down, washing up and down in this thick soupy atmosphere on Venus and so they’re slowed down and that in turn makes the pitch of the voice drop, so a soprano turns in a bass.

AS: That’s Professor Timothy Leighton, who is an acoustician at the University of Southampton. Tim recently made the headlines by creating an algorithm which can predict how your voice would sound on a different planet. He found some surprising results – including…

TL: We sound like bass Smurfs when we speak on Venus.

AS: When the keen ears of Dr Jenny Shipway pricked up at the sound of bass Smurfs, she knew she wanted to hear more from Professor Leighton. You see, Jenny is the manager of the planetarium at the Intech Science Centre, just outside Winchester. She runs a show called Flight through the Universe… would-be space explorers sit down in the comfy seats, look up at the inside of the planetarium’s dome and then the stars appear. Jenny narrates the live show, whizzing her charges through the sights of space.

Dr Jenny Shipway: What a great way to make the invisible atmosphere kind of audible. you can hear the atmosphere is different and normally that would just be completely invisible to the audience.

AS: So to bring the atmospheres of the various planets and moons to life, Jenny has incorporated Tim’s research into her show. I went along to Intech and the planetarium for one of the first showings to hear how it all comes together. First, Jenny’s colleague James finds a volunteer…

James: Hello there, we’re doing a show called Flight through the Universe that you’re waiting to see and part of the show is we’re going to record somebody’s voice and let them know what it sounds like when you’re on Venus and some of the other moons in the solar system. Would you like to do the voice recording?

Rhys: Yeah, sure.

James: Excellent, thanks very much. What’s your name, by the way?

Rhys: Rhys.

James: Well, thank you very much, Rhys. OK, that’s great.

AS: Rhys, how do you feel about the idea of your voice being heard on a different planet?

Rhys: Quite cool, ‘cos it’s kind of so different.

AS: Then, James takes Rhys in to the planetarium before any other member of the public is allowed in, to record his voice…

Jenny recording Rhys’s voice.

AS: And finally, once the audience is in the planetarium and Jenny is halfway through the show, she brings in the recording to show everyone how Rhys could sound on Venus….

Clip from Flight through the Universe, with Jenny’s narration.

AS: After the show, I asked Rhys what he thought he sounded like…

Rhys: Like a robot or an alien. It’s really weird.

AS: Well you are an alien ‘cos you’re on a different planet.

Rhys: Fair enough.

AS: So how on Earth – er, Venus – did Tim make this calculation? Tim studies all sorts of sounds – he first got into it when he was a young man trying to figure out why brooks babble. Studying the sounds made by bubbles of air in water has even helped scientists to calculate how much carbon dioxide the ocean absorbs from the atmosphere, which is a really useful measure of climate change.

But Tim’s not content with listening in to sounds on earth. When the European Space Agency probe known as Huygens touched down on Saturn’s moon Titan in 2005, Tim wondered why it didn’t have a microphone on board.

TL: I thought, if we’d had a microphone and everything on this probe Huygens had failed sadly and and it landed with a splash as opposed to a crunch and we heard that, we would know that we’d hit the first lake that we’d ever discovered in the universe outside the Earth.

The first lake that’s open to an atmosphere, so we thought that would be interesting. but then I said to myself, well, hang on, if this probe splashes into a lake made of liquid ethane and methane, I’m assuming I could recognise that. So what we did was we simulated the sound using all this knowledge that we’d gained over the years from the work on climate change and such like and listening to the oceans to generate the sound of this splashdown. And it turns out it does sound alien, compared to a splash on Earth, but it’s recognisable.

AS: As it happens, Huygens had landed on solid ground, not a lake. But Tim’s curiosity persisted. With his colleague Andy White, Tim then simulated the sound of a waterfall made of liquid ethane and methane on Titan.

TL: We did thunder and lightning on various worlds, we did a cryo-volcano, that’s a volcano spewing up ice water on Titan and we looked at the sound of dust devils on Mars, all these different things.

AS: And then, of course, he started to think about how a person would sound on Titan. Of course, the human voice is very different to the sound of a dust devil because humans are so good at picking up all the nuances in a person’s voice.

TL: There wa no way we could simulate a human voice from scratch so what we decided to do with the voice was set up software that could morph it and change it.

AS: Tim and his colleagues had to take into account the various cues we use to interpret a person’s voice. This included pitch, which is defined by how fast your vocal cords vibrate when you speak, and the echoes that bounce up and down your windpipe when you talk. You might not think you’re paying attention to these, but your brain is subconsciously listening in and deciding whether the thing making a vocal noise is large or small.

TL: Every time these vocal cords are beating up and down, these echoes are going up and down our windpipe. We’re barely conscious of the fact that we’re appreciating them. They whip up and down the windpipe very fast on Venus because the sound speed is very high. Now our brain thinks we’re speaking on Earth, so it thinks the tube is short. So these echoes come back very soon and our brain says, well this is a short windpipe, therefore this is coming from a small creature. So we put those two bits of information – small creature, bass voice – and so we sound like bass Smurfs when we speak on Venus.

AS: Bass smurfs, spaceboys, robots, aliens… we might be stuck on Earth because of gravity and the expense of rockets but our imaginations know no bounds. Hearing from all these cosmologists, astrophysicists and acousticians makes you realise that science is about imagination too. I might be so in love with gorgeous images of space taken by telescopes that I hadn’t ever thought about what things sound like up there.

TL: Science is about proposing something using your best theory, making a prediction and then going along and testing it, so I did this to place people in that invisible part of science, where most scientists exist most of the time, which is between the theory and the test.

AS: It’s a good job there’s enough scientists to keep imagining new ways of seeing the world and testing how it works.

Remember you can read the transcript and visit links to the research mentioned in this podcast at our website, And don’t forget to tell us what you make of these weird and wacky sounds of space – tweet us @PodAcademy.









Thesoundofmusicandvoicesinspacepart 1: theory

Thesoundofmusicandvoicesinspacepart 2: modelingandsimulation



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