How radio telescopes show us unseen galaxies | Natasha Hurley-Walker

185,808 views ・ 2017-05-16

TED


Please double-click on the English subtitles below to play the video.

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Transcriber: Joseph Geni Reviewer: Joanna Pietrulewicz
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Space, the final frontier.
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I first heard these words when I was just six years old,
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and I was completely inspired.
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I wanted to explore strange new worlds.
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I wanted to seek out new life.
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I wanted to see everything that the universe had to offer.
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And those dreams, those words, they took me on a journey,
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a journey of discovery,
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through school, through university,
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to do a PhD and finally to become a professional astronomer.
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Now, I learned two amazing things,
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one slightly unfortunate,
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when I was doing my PhD.
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I learned that the reality was
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I wouldn't be piloting a starship anytime soon.
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But I also learned that the universe is strange, wonderful and vast,
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actually too vast to be explored by spaceship.
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And so I turned my attention to astronomy, to using telescopes.
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Now, I show you before you an image of the night sky.
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You might see it anywhere in the world.
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And all of these stars are part of our local galaxy, the Milky Way.
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Now, if you were to go to a darker part of the sky,
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a nice dark site, perhaps in the desert,
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you might see the center of our Milky Way galaxy
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spread out before you, hundreds of billions of stars.
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And it's a very beautiful image.
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It's colorful.
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And again, this is just a local corner of our universe.
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You can see there's a sort of strange dark dust across it.
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Now, that is local dust
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that's obscuring the light of the stars.
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But we can do a pretty good job.
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Just with our own eyes, we can explore our little corner of the universe.
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It's possible to do better.
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You can use wonderful telescopes like the Hubble Space Telescope.
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Now, astronomers have put together this image.
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It's called the Hubble Deep Field,
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and they've spent hundreds of hours observing just a tiny patch of the sky
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no larger than your thumbnail held at arm's length.
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And in this image
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you can see thousands of galaxies,
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and we know that there must be hundreds of millions, billions of galaxies
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in the entire universe,
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some like our own and some very different.
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So you think, OK, well, I can continue this journey.
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This is easy. I can just use a very powerful telescope
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and just look at the sky, no problem.
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It's actually really missing out if we just do that.
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Now, that's because everything I've talked about so far
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is just using the visible spectrum, just the thing that your eyes can see,
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and that's a tiny slice,
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a tiny, tiny slice of what the universe has to offer us.
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Now, there's also two very important problems with using visible light.
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Not only are we missing out on all the other processes
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that are emitting other kinds of light,
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but there's two issues.
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Now, the first is that dust that I mentioned earlier.
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The dust stops the visible light from getting to us.
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So as we look deeper into the universe, we see less light.
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The dust stops it getting to us.
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But there's a really strange problem with using visible light
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in order to try and explore the universe.
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Now take a break for a minute.
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Say you're standing on a corner, a busy street corner.
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There's cars going by.
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An ambulance approaches.
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It has a high-pitched siren.
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(Imitates a siren passing by)
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The siren appeared to change in pitch
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as it moved towards and away from you.
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The ambulance driver did not change the siren just to mess with you.
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That was a product of your perception.
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The sound waves, as the ambulance approached,
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were compressed,
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and they changed higher in pitch.
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As the ambulance receded, the sound waves were stretched,
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and they sounded lower in pitch.
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The same thing happens with light.
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Objects moving towards us,
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their light waves are compressed and they appear bluer.
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Objects moving away from us,
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their light waves are stretched, and they appear redder.
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So we call these effects blueshift and redshift.
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Now, our universe is expanding,
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so everything is moving away from everything else,
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and that means everything appears to be red.
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And oddly enough, as you look more deeply into the universe,
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more distant objects are moving away further and faster,
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so they appear more red.
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So if I come back to the Hubble Deep Field
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and we were to continue to peer deeply into the universe
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just using the Hubble,
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as we get to a certain distance away,
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everything becomes red,
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and that presents something of a problem.
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Eventually, we get so far away
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everything is shifted into the infrared
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and we can't see anything at all.
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So there must be a way around this.
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Otherwise, I'm limited in my journey.
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I wanted to explore the whole universe,
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not just whatever I can see, you know, before the redshift kicks in.
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There is a technique.
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It's called radio astronomy.
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Astronomers have been using this for decades.
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It's a fantastic technique.
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I show you the Parkes Radio Telescope, affectionately known as "The Dish."
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You may have seen the movie.
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And radio is really brilliant.
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It allows us to peer much more deeply.
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It doesn't get stopped by dust,
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so you can see everything in the universe,
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and redshift is less of a problem
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because we can build receivers that receive across a large band.
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So what does Parkes see when we turn it to the center of the Milky Way?
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We should see something fantastic, right?
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Well, we do see something interesting.
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All that dust has gone.
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As I mentioned, radio goes straight through dust, so not a problem.
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But the view is very different.
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We can see that the center of the Milky Way is aglow,
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and this isn't starlight.
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This is a light called synchrotron radiation,
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and it's formed from electrons spiraling around cosmic magnetic fields.
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So the plane is aglow with this light.
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And we can also see strange tufts coming off of it,
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and objects which don't appear to line up
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with anything that we can see with our own eyes.
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But it's hard to really interpret this image,
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because as you can see, it's very low resolution.
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Radio waves have a wavelength that's long,
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and that makes their resolution poorer.
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This image is also black and white,
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so we don't really know what is the color of everything in here.
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Well, fast-forward to today.
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We can build telescopes
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which can get over these problems.
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Now, I'm showing you here an image of the Murchison Radio Observatory,
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a fantastic place to build radio telescopes.
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It's flat, it's dry,
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and most importantly, it's radio quiet:
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no mobile phones, no Wi-Fi, nothing,
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just very, very radio quiet,
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so a perfect place to build a radio telescope.
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Now, the telescope that I've been working on for a few years
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is called the Murchison Widefield Array,
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and I'm going to show you a little time lapse of it being built.
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This is a group of undergraduate and postgraduate students
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located in Perth.
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We call them the Student Army,
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and they volunteered their time to build a radio telescope.
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There's no course credit for this.
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And they're putting together these radio dipoles.
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They just receive at low frequencies, a bit like your FM radio or your TV.
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And here we are deploying them across the desert.
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The final telescope covers 10 square kilometers
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of the Western Australian desert.
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And the interesting thing is, there's no moving parts.
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We just deploy these little antennas
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essentially on chicken mesh.
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It's fairly cheap.
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Cables take the signals
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from the antennas
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and bring them to central processing units.
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And it's the size of this telescope,
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the fact that we've built it over the entire desert
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that gives us a better resolution than Parkes.
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Now, eventually all those cables bring them to a unit
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which sends it off to a supercomputer here in Perth,
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and that's where I come in.
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(Sighs)
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Radio data.
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I have spent the last five years
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working with very difficult, very interesting data
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that no one had really looked at before.
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I've spent a long time calibrating it,
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running millions of CPU hours on supercomputers
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and really trying to understand that data.
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And with this telescope,
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with this data,
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we've performed a survey of the entire southern sky,
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the GaLactic and Extragalactic All-sky MWA Survey,
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or GLEAM, as I call it.
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And I'm very excited.
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This survey is just about to be published, but it hasn't been shown yet,
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so you are literally the first people
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to see this southern survey of the entire sky.
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So I'm delighted to share with you some images from this survey.
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Now, imagine you went to the Murchison,
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you camped out underneath the stars
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and you looked towards the south.
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You saw the south's celestial pole,
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the galaxy rising.
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If I fade in the radio light,
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this is what we observe with our survey.
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You can see that the galactic plane is no longer dark with dust.
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It's alight with synchrotron radiation,
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and thousands of dots are in the sky.
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Our large Magellanic Cloud, our nearest galactic neighbor,
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is orange instead of its more familiar blue-white.
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So there's a lot going on in this. Let's take a closer look.
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If we look back towards the galactic center,
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where we originally saw the Parkes image that I showed you earlier,
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low resolution, black and white,
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and we fade to the GLEAM view,
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you can see the resolution has gone up by a factor of a hundred.
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We now have a color view of the sky,
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a technicolor view.
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Now, it's not a false color view.
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These are real radio colors.
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What I've done is I've colored the lowest frequencies red
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and the highest frequencies blue,
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and the middle ones green.
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And that gives us this rainbow view.
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And this isn't just false color.
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The colors in this image tell us about the physical processes
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going on in the universe.
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So for instance, if you look along the plane of the galaxy,
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it's alight with synchrotron,
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which is mostly reddish orange,
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but if we look very closely, we see little blue dots.
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Now, if we zoom in,
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these blue dots are ionized plasma
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around very bright stars,
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and what happens is that they block the red light,
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so they appear blue.
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And these can tell us about these star-forming regions
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in our galaxy.
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And we just see them immediately.
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We look at the galaxy, and the color tells us that they're there.
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You can see little soap bubbles,
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little circular images around the galactic plane,
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and these are supernova remnants.
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When a star explodes,
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its outer shell is cast off
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and it travels outward into space gathering up material,
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and it produces a little shell.
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It's been a long-standing mystery to astronomers
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where all the supernova remnants are.
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We know that there must be a lot of high-energy electrons in the plane
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to produce the synchrotron radiation that we see,
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and we think they're produced by supernova remnants,
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but there don't seem to be enough.
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Fortunately, GLEAM is really, really good at detecting supernova remnants,
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so we're hoping to have a new paper out on that soon.
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Now, that's fine.
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We've explored our little local universe,
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but I wanted to go deeper, I wanted to go further.
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I wanted to go beyond the Milky Way.
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Well, as it happens, we can see a very interesting object in the top right,
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and this is a local radio galaxy,
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Centaurus A.
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If we zoom in on this,
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we can see that there are two huge plumes going out into space.
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And if you look right in the center between those two plumes,
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you'll see a galaxy just like our own.
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It's a spiral. It has a dust lane.
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It's a normal galaxy.
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But these jets are only visible in the radio.
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If we looked in the visible, we wouldn't even know they were there,
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and they're thousands of times larger than the host galaxy.
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What's going on? What's producing these jets?
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At the center of every galaxy that we know about
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is a supermassive black hole.
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Now, black holes are invisible. That's why they're called that.
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All you can see is the deflection of the light around them,
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and occasionally, when a star or a cloud of gas comes into their orbit,
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it is ripped apart by tidal forces,
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forming what we call an accretion disk.
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The accretion disk glows brightly in the x-rays,
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and huge magnetic fields can launch the material into space
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at nearly the speed of light.
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So these jets are visible in the radio
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and this is what we pick up in our survey.
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Well, very well, so we've seen one radio galaxy. That's nice.
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But if you just look at the top of that image,
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you'll see another radio galaxy.
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It's a little bit smaller, and that's just because it's further away.
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OK. Two radio galaxies.
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We can see this. This is fine.
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Well, what about all the other dots?
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Presumably those are just stars.
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They're not.
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They're all radio galaxies.
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Every single one of the dots in this image
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is a distant galaxy,
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millions to billions of light-years away
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with a supermassive black hole at its center
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pushing material into space at nearly the speed of light.
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It is mind-blowing.
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And this survey is even larger than what I've shown here.
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If we zoom out to the full extent of the survey,
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you can see I found 300,000 of these radio galaxies.
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So it's truly an epic journey.
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We've discovered all of these galaxies
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right back to the very first supermassive black holes.
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I'm very proud of this, and it will be published next week.
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Now, that's not all.
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I've explored the furthest reaches of the galaxy with this survey,
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but there's something even more in this image.
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Now, I'll take you right back to the dawn of time.
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When the universe formed, it was a big bang,
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which left the universe as a sea of hydrogen,
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neutral hydrogen.
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And when the very first stars and galaxies switched on,
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they ionized that hydrogen.
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So the universe went from neutral to ionized.
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That imprinted a signal all around us.
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Everywhere, it pervades us,
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like the Force.
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Now, because that happened so long ago,
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the signal was redshifted,
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so now that signal is at very low frequencies.
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It's at the same frequency as my survey,
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but it's so faint.
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It's a billionth the size of any of the objects in my survey.
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So our telescope may not be quite sensitive enough to pick up this signal.
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However, there's a new radio telescope.
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So I can't have a starship,
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but I can hopefully have
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one of the biggest radio telescopes in the world.
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We're building the Square Kilometre Array, a new radio telescope,
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and it's going to be a thousand times bigger than the MWA,
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a thousand times more sensitive, and have an even better resolution.
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So we should find tens of millions of galaxies.
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And perhaps, deep in that signal,
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I will get to look upon the very first stars and galaxies switching on,
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the beginning of time itself.
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Thank you.
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(Applause)
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