The biggest ever telescope

The square kilometre array is set to be the biggest telescope, but how does it work?
08 September 2020

Interview with 

Phillip Diamond, Square Kilometre Array Organisation


An image of a spiral galaxy


Work is underway on an equivalently impressive project, which will be the most powerful telescope we’ve ever built. It’ll enable us to see at least 10 times further than we can already. It’s the Square Kilometre Array or SKA, which is a radio telescope, and it’s unusual because it’s going to span continents: part of it is in Australia, and the rest is in southern Africa. The HQ though is in the UK at Jodrell Bank Observatory, and the Director General is Phillip Diamond, who spoke to Chris Smith about the project...

Phillip - Well, there are different types of light. So, yes, Galileo observed visible light that we see with our eyes, but other types of lights across the, what we call the electromagnetic spectrum are x-ray, ultraviolet light, the visible is sort of in the middle of the electromagnetic spectrum. So radio waves are what we call long wavelength - part of the electromagnetic spectrum. And in order to observe the universe in radio waves, we need to build large dishes to pick up this long wavelength radiation, and so using big dishes like that at Jodrell bank, which is 76 metres across.

Chris - What can radio waves, and those other sorts of radiation cause they're effectively forms of light that we can't see aren't they, what can they tell you about a distant object that I couldn't learn from say looking at it with the Hubble space telescope?

Phillip - Well, if you could see the universe with radio light as we do, it looks remarkably different actually from observing with visible light. So with visible light, you pick out the stars, the very bright objects like stars and galaxies etc. With radio waves, we pick up a lot of gas, very energetic phenomena, the jets exploding from black holes. But one of the main things that we can do is observe hydrogen - the most common element in the universe. And that is only visible in the radio part of the electromagnetic spectrum.

Chris - Why does it matter that you're seeing hydrogen? Why is that important?

Phillip - It is the most common element in the universe and therefore it's the constituent of much of what is out there, it forms the majority of the material in stars, the majority within galaxies, it traces the dynamics of galaxies. And as we look further and further into the universe, closer to the big bang, we can actually use observations of hydrogen to watch the universe evolve in time to what we see when we look out into space now.

Chris - The thing about the universe is that we believe that it began with a big bang that was about 13.8 billion years ago or so, but initially it was far too hot for anything to exist. Hydrogen didn't exist. So does that mean there's a limit to how far back in time you could look? If you can see hydrogen?

Phillip - There is - it's about 400 million years after the start of the big bang, where we start to see the hydrogen in the universe beginning to form the first stars and the first galaxies, at least we presume that to be the case. It's with the SKA that we actually hope to see this for the first time to understand the details of how those first stars and first galaxies were formed. And then what we want to do is essentially make a movie of how the universe evolves in time from that point to about 400 million years after the big bang.

Chris - One of the striking things about it is that you've got multiple countries involved and it's spread over a huge distance. Now, why is that? Why not just have one big dish in one place.

Phillip - A big dish, like the Lovell telescope is 76 metres in diameter. The largest big dish in the world which could move is a Green Bank West Virginia, which is just over a hundred metres. We'd like to build bigger dishes, but that's just not practical. In the fifties and sixties, what was realised was if we had smaller dishes that we connected back then with copper cables, but now with fibre optics, and spread them apart, we could essentially synthesise a much larger dish, especially if we had many of these smaller dishes. But if you think of the big dishes as like a wide angle lens, then with what we call interferometers moving the smaller dishes apart, it's like a zoom lens.

Chris - And just out of interest, how much data will be flowing down these fibre-optics to collect all this information from this enormous array of dishes?

Phillip - Well, the volumes are truly huge. So the raw data we will generate from the dishes is essentially the same scale as the entire internet of the planet, but it's on our own dedicated network. And it's just not as chaotic as the data that flows over the internet. We have fixed formats that we control through this dedicated network. We quickly reduce the volumes of data, they're still enormous, we'll be generating on the order of 700 petabytes a year into the archive for the astronomers to use. And that dwarf's the total generated by Facebook and Google, for example. So it really is a big data problem that we're tackling to deliver this new science to users.

Chris - And you've mentioned obviously giving us an insight, hopefully, into the earliest times of the universe's existence, what other projects have you got earmarked for this once it goes live?

Phillip - Well, our global science community has actually generated the science case, which is about 2000 pages long. It's a huge, huge range of science, but a couple of examples - one is that we'll be looking for the origins of life itself. We'll be trying to detect the molecular signatures of prebiotic molecules and potentially even amino acids. If we discover that is widespread out there in the universe, that will have very interesting implications for the origins of life. And another, to connect back to LIGO, for example, we will also be looking for gravitational waves. We'll be doing this by looking at the signals from pulsars, which are the rotating remnants of large stars, which have exploded. We'll be looking at these networks of pulsars across the universe and seeing the ripples of gravitational waves as they pass through.


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