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