Natasha Hurley-Walker: How Do Radio Telescopes Reveal The Universe We Can't See?

Feb 9, 2018
Originally published on February 9, 2018 7:31 am

Part 3 of the TED Radio Hour episode Peering Deeper Into Space.

About Natasha Hurley-Walker's TED Talk

Natasha Hurley-Walker explains how a new radio telescope helps us "see" without light. She says these telescopes can tell us about millions of galaxies — and maybe even the beginning of time.

About Natasha Hurley-Walker

Astronomer Natasha Hurley-Walker is a research fellow at the International Centre for Radio Astronomy Research Lab at Curtin University in Perth, Australia.

She recently helped complete a radio telescope survey of the entire southern sky, called the GLEAM survey. She is also helping to design what will become the world's largest radio telescope, set to come out in the mid 2020s.

Copyright 2018 NPR. To see more, visit http://www.npr.org/.

GUY RAZ, HOST:

Must be really, really dark at night in the Australian desert.

NATASHA HURLEY-WALKER: It's just phenomenal. I mean, no lights. You see the Milky Way stream up above the horizon, billions of stars casting this huge glow over the desertscape. I'm getting goosebumps just thinking about it.

RAZ: This is Natasha Hurley-Walker. She's a radio astronomer.

HURLEY-WALKER: Yeah, that's right. So I'm an astrophysicist who uses radio telescopes and supercomputers to explore our universe.

RAZ: And radio telescopes like the one Natasha works with, they're a lot different than optical telescopes. And if you just imagine an optical telescope for a second, you probably think of a tube with lenses and mirrors. And they're all designed to observe visible light waves coming from outer space, but radio telescopes are made up of multiple dishes or metal receivers. And these telescopes are designed to observe radio waves, which is why Natasha works in the desert outside Perth, in Western Australia.

HURLEY-WALKER: Right. Because we have a fantastically radio-quiet site up in the desert where there's a radio exclusion zone. There's only about a hundred people in an area about the size of the Netherlands. So the quality of the reception we can get in terms of radio is phenomenal.

RAZ: Now, radio astronomers like Natasha work with radio telescopes because optical telescopes have some limitations. Natasha explains from the TED stage.

(SOUNDBITE OF TED TALK)

HURLEY-WALKER: If you were to go to a darker spot of the sky, you might see the center of our Milky Way galaxy spread out before you, hundreds and billions of stars. Just with our own eyes, we can explore a little corner of the universe. It's possible to do better. You can use wonderful telescopes like the Hubble Space Telescope. Now, astronomers have put together this image. It's called the Hubble Deep Field. And in this image, you can see thousands of galaxies, and we know that there must be hundreds of millions, billions of galaxies in the entire universe. So you think, OK, well, I can continue this journey. This is easy. I can just use a very powerful telescope and just look at the sky, no problem. Actually, we're really missing out if we just do that. Now, that's because everything I've talked about so far is just using the visible spectrum, just the thing that your eyes can see. And that's a tiny slice - a tiny, tiny slice of what the universe has to offer us. Now, say you're standing on a corner. An ambulance approaches. It has a high-pitched siren. (Imitating siren noise). The siren appeared to change in pitch as it moved towards and away from you. The sound waves as the ambulance approached were compressed, and they changed higher in pitch. As the ambulance receded, the sound waves were stretched, and they sounded lower in pitch. The same thing happens with light. Objects moving towards us, their light waves are compressed and they appear bluer. Objects moving away from us, their light waves are stretched, and they appear redder. We call these effects blue shift and red shift. Our universe is expanding so everything is moving away from everything else, and that means everything appears to be red. Now, eventually we get so far away, everything has shifted into the infrared, and we can't see anything at all.

RAZ: So is it at that point where we need radio telescopes to look even further beyond what an optical telescope can see?

HURLEY-WALKER: Yeah. So if you just look at optical telescopes, basically the universe kind of thins out. It gets red and then kind of vanishes. So we build infrared space telescopes. Now, that's more difficult because the universe has a lot of infrared stuff in it. So all the gas in our galaxy, all of the exploding stars, they produce a lot of infrared, as well. So there's a lot of contamination in that signal. The nice thing about radio is it does just punch through.

RAZ: So how has the technology of these telescopes changed or improved in the past few years?

HURLEY-WALKER: So some of the technology has changed, but for the low-frequency radio astronomy, we were doing that back in the '50s and '60s. The very first person to build a radio telescope was Grote Reber. He just went, OK, I've heard about people picking up radio from the stars. I'm going to build an imaging telescope, and I'm going to make a map of the Milky Way. And he just did it in his backyard in his spare time. That map is still accurate. It's still dead-on today. What has changed is the competing. So originally, we could only build radio telescopes with one or two elements. But nowadays, we have incredible supercomputers so we can put down many telescopes in all different locations and then knit the signals together. So my telescope, for instance, has 128 different elements and it knits them all together seamlessly to produce these incredible images of the sky. So it's really about the computing. That's what makes that possible.

(SOUNDBITE OF MUSIC)

RAZ: In just a minute, the amazing things Natasha and her team discovered by using those radio telescopes and supercomputers. I'm Guy Raz, and you're listening to the TED Radio Hour from NPR.

(SOUNDBITE OF MUSIC)

RAZ: It's the TED Radio Hour from NPR. I'm Guy Raz. And on the show today - Peering Deeper Into Space. And before the break, we were talking with Natasha Hurley-Walker. She's been doing research using a new radio telescope in the desert of Western Australia. And from the TED stage, Natasha showed off some of the results of her observations.

(SOUNDBITE OF TED TALK)

HURLEY-WALKER: I have spent the last five years working with very difficult, very interesting data that no one had really looked at before. So I'm delighted to share with you some images from this survey. The colors in this image tell us about the physical processes going on in the universe. So for instance, this is the local radio galaxy Centaurus A. If we zoom in on this, we can see that there are two huge plumes going out into space. And if you look right in the center between those two plumes, you'll see a galaxy just like our own. But if we looked in the visible, we wouldn't even know they were there. And they're thousands of times larger than the host galaxy. Well, what's going on? What's producing these jets?

At the center of every galaxy that we know about is a supermassive black hole. Now, black holes are invisible. All you can see is the deflection of the lights around them. And occasionally when a star or a cloud of gas comes into their orbit, it is ripped apart by tidal forces forming what we call an accretion disk. The accretion disk glows brightly in the X-rays, and huge magnetic fields can launch the material into space. So these jets are visible in the radio, and this is what we pick up in our survey. All very well, so we've seen one radio galaxy.

But if you just look at the top of that image, you'll see another radio galaxy. It's a little bit smaller, and that's just because it's further away - OK, two radio galaxies. Well, what about all the other dots? Presumably, those are just stars. They're not. They're all radio galaxies. Every single one of the dots in this image is a distant galaxy millions to billions of light-years away with a supermassive black hole at its center, pushing material into space at nearly the speed of light. It is mind-blowing. And this survey is even larger than what I've shown here. If we zoom out to the full extent of the survey, you can see I've found 300,000 of these radio galaxies. So it's truly a epic journey. We've discovered all of these galaxies right back to the very first supermassive black holes.

(SOUNDBITE OF MUSIC)

RAZ: Is there a limit? I mean, is there a fixed point where we just won't be able to observe beyond that point?

HURLEY-WALKER: Essentially, yes. We will never be able to observe outside our own light horizon. So if you think back that the universe is 13.67 billion years old - if you look 13.67 billion light-years away, you see back in time. And you're looking at like nothing. So we can't see outside this bubble that's about 13.7 billion light-years in radius. But we don't know that that is the size of the universe. So while I was in Cambridge visiting the Department of Applied Mathematics and Theoretical Physics, which is where Stephen Hawking works - and I go to all the seminars - I went to one which was called Observable Limits of the Universe.

And it was almost comprehensible at least for about five slides, and then I got lost. There was a lot of math. Anyway, the authors concluded that the universe is at least 30 times larger than what we can see in our light horizon. So if you imagine we're looking at a sphere, the volume of that sphere - 13.67 billion light-years cubed times four-thirds pi - times that by 30. That is the minimum size of the universe. But they didn't rule out the universe being infinitely sized, which is really hard to get your head around.

RAZ: I mean, it's incredible that the scope of our understanding and knowledge of the cosmos has expanded in such a way that we probably know and have learned more in the past five years than we learned, like, in the previous 25 years, right?

HURLEY-WALKER: Absolutely.

RAZ: And presumably there's going to be more and bigger things coming at us in the near future.

HURLEY-WALKER: I think what's really become clear over the last decade is that the questions we're now asking require hundreds of scientists - thousands of scientists working really in coordination and collaboration on really enormous projects. But even amongst all that - all these huge megaprojects, there's still like little teams just coming up with really clever ideas and putting some stuff in the field. So I guess one example - like our telescope started out as a real kind of just some-cowboys-in-the-desert-type thing. So originally the Murchison Widefield Array was just a few dipoles, and we just, you know, were taking measurements. And then we built two elements. And then we built four elements. And then we built eight elements. And so we're sort of slowly building up this idea of how to build a really great radio telescope. So there's these huge megaprojects, but there's also still little groups just doing cool things. So yeah, I just think it's a fantastic time to be in science. It's really exciting.

(SOUNDBITE OF MUSIC)

RAZ: Natasha Hurley-Walker - she's an astronomer working at the International Centre for Radio Astronomy Research at Curtin University in Perth, Australia. You can see her entire talk at TED.com. Transcript provided by NPR, Copyright NPR.