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How radio telescopes show us unseen galaxies

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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.
  • 15:06 - 15:07
    Thank you.
  • 15:07 - 15:10
    (Applause)
Title:
How radio telescopes show us unseen galaxies
Speaker:
Natasha Hurley-Walker
Description:

Our universe is strange, wonderful and vast, says astronomer Natasha Hurley-Walker. A spaceship can't carry you into its depths (yet) -- but a radio-telescope can. In this mesmerizing, image-packed talk, Hurley-Walker shows how she probes the mysteries of the universe using special technology that reveals light spectrums we can't see.

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Video Language:
English
Team:
TED
Project:
TEDTalks
Duration:
15:25

English subtitles

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