All language subtitles for BBC.The.Sky.at.Night.2023.The.Very.Large.Telescope.1080p.HDTV.x264.AAC.MVGroup.org

In the heart of Chile's Atacama
Desert lies one of the most advanced

observatories in the world.

These eyes on the sky have been at
the forefront of ground-based

optical astronomy for 25 years.

The VLT, or Very Large Telescopes,
have been instrumental in some

of the greatest astronomical
discoveries of all time.

They have led to Nobel Prizes
and transformed our understanding

of the universe.

In this special episode
of The Sky at Night,

I'm here in Chile at the VLT.

These telescopes are operated by the
European Southern Observatory,

or ESO.

It sits at 2,635 metres on
the Paranal mountain

and consists of four 8.2m
main telescopes

and an additional four
1.8m movable ones.

These telescopes can work
individually or all together

to see the finest of astronomical
details, making this site home

to the world's most advanced
optical instrument,

with a long history of
celestial firsts.

I've come to meet the scientists
and engineers behind this

incredible technological feat
to learn what it takes

to run this flagship facility...

To see the sun setting here
every night,

it's still an amazing experience.

..and uncover some secrets.

Welcome to The Sky at Night.

The Very Large Telescope is located
at the Paranal Observatory,

in the Atacama Desert, one of
the driest places on Earth -

providing a perfect home for its
state-of-the-art Unit Telescopes.

The VLT, or the Very Large
Telescope, is actually made up

of four main telescopes,

that can work as individuals or have
their observing power combined.

Each one of these beasts
is 8.2m in diameter.

The thickness is just 17.5cm.

Any thicker and they would collapse
under their own weight.

Every day at sunset,
the telescope dome opens up

to the sky for the night.

But over time, the mirrors
accumulate dust,

affecting their reflectivity and,
therefore, image quality.

Around every 18 months, the enormous
mirrors have to be cleaned

and recoated.

Cleaning a telescope mirror is a
delicate and nerve-racking process.

The mirror itself weighs 23 tonnes,

and it's shipped from the telescope
to this facility in its cell.

Once here, the old coating
will be removed

and a new one applied.

But we're incredibly lucky,
because the mirror is actually

in this facility at the moment,
and so we can see some

of that coating process.

Hello. Hey, Maggie.
Good to see you. Nice to see you.

We'll go see the cleaning process?
Yeah, sure. Perfect. Let's go.

Head of Paranal's maintenance,
support and engineering,

Maxime Boccas is in charge
of the operation.

Maxime, what are we looking at here?

So, the dust is basically the dust
that is in the environment,

picked up from the ground
by the winds

and deposited slowly on the glass.

So, how often does this
process happen?

We do that every two years,
because we find that it's on average

the sweet spot for the astronomers
that want a dirty mirror

and for the engineers that have to
do the heavy work to clean it.

During these ten days that we have
to shut down the whole telescope,

there is no astronomy, no science.

Yes, yes.

So, you do this as quickly
but as delicately as possible.

Super delicate.

With the mirror safely removed
from the telescope,

it's time to start cleaning.

Firstly, with a bit of good old soap
and water.

They are going to start rotating
this arm above the surface,

and pouring water first,

so that we can remove the biggest
particles of dust,

and then they will add soap.

The soap will help to actually
remove the stuck particles. Yes.

And once we are finished with
this first rough cleaning,

we'll put chemicals on,

and the chemical will actually
strip, remove... Oh, the aluminium.

..the aluminium layer that is
on the glass.

And when we're happy that
the thing is fully dry,

then that's time to move it
to the vacuum vessel.

After being stripped
of its aluminium surface,

it's time for the squeaky clean
mirror to be recoated.

This is where it will regain
its reflective properties.

And so, what will happen is, once
the mirror's cleaned, they'll take

that... The bottom half and the
mirror to that chamber. Correct.

And that's where the sputtering
takes place? Exactly. Yes.

So, can you explain what
sputtering is?

What you do is, basically, you
bombard a very pure plate of metal,

the metal that you want to deposit -
in our case, aluminium - with ions.

OK. It's like basically painting,
because the mirror will be rotating

under that plate.
We'll be painting radial lines

across the glass, until we have
done a full revolution.

So, how much aluminium?
Because we've got an 8m mirror.

But how much aluminium is actually
deposited? It's very little.

So, I've actually brought
a soda can here.

Yes. All right?

When it's empty, it's about 10-12g.
Yes.

And that's the amount of aluminium
that will be deposited

in a very, very thin layer
on the mirror.

Cleaning and recoating a mirror
of this size doesn't come

without its challenges.

The challenge, basically,
is homogeneity of the process.

The whole mirror - because it's
so big - the 40 square metres

have to be cleaned the same way.
Yes.

And then, of course, doing the
vacuum has its own challenges,

depositing exactly the right
thickness. Yes.

So, everything has to be adjusted
like a watch.

When I was a child, I made my own
little telescope mirror -

just 150mm across - and it went
through the same process.

But this is much bigger.
Much bigger. Yes!

It's time for this freshly coated
mirror to get back into action

with some astronomy at the VLT.

I'm travelling to the control room,

a hub of astronomical discovery,
to meet Joe Anderson,

who is currently on the day shift.

Hi, Joe. Hi.

So, your title here,
you're staff astronomer?

Yeah, I'm ESO staff astronomer.
OK, yes.

So, my job here is to work
at night-time,

sometimes during the day.

When we're working at night, then
we're working with the telescopes,

with the instruments to take
scientific observations

for the astronomical community
here at Paranal.

Joe is one of the astronomers who
looks after the VLT's instruments,

collecting data for other
astronomers in different countries

around the world.

So, here we have four telescopes.

On each telescope, we have
three different instruments.

We're obtaining those photons
on our instruments,

and then that data is available,
pretty much, in real time

on the internet for people
to download.

And so, the user then can
download those data

and start analysing those data.
Oh, perfect.

That must be a lovely moment.
Yes, indeed.

Joe's time is split into thirds -

two for ESO duties, like looking
after the instruments,

and one third for his own research.

You also get the opportunity to
do research of your own?

Yes. Yes, indeed. I spend some of
my time doing my own research.

I work in supernovae. So, supernovae
are the stars that explode.

And my main focus is trying to
understand which types of stars

are going to explode to
which type of supernovae.

And you've got some data to show us?
Yeah.

So, I can show you some spectra
that we take here.

This gives you information
about the properties.

So, if you're looking at a star,

it can tell you how many...how much
heavy metals it has.

It can give you information,
if you're looking at galaxies,

of how many stars are forming in
different parts of galaxies

by using different what you call
spectral lines

that you see at different
wavelengths,

different colours within
the spectra.

Joe and his team use an
instrument known as MUSE,

the Multi-Unit Spectroscopic
Explorer,

to help understand which type of
star is going to explode.

So, this is SN 2018ie.

OK, yes.

A supernova that occurred in 2018?

Exactly, exactly. Yes.

And then the image we show here
in the middle,

this is now just showing the places
where the stars are forming.

And so, then we extract the
information where the supernova

occurred, but we also extract it
in all these other places where

the stars have been formed - and
this is what's shown at the bottom.

And the colour scale here is
basically the chemical composition.

So, then we can ask the question,
well, the chemical composition

where the supernova exploded,
is this higher or lower

than the rest of these
star-forming regions?

Have you drawn any conclusions?
Yes.

We see that it's much more probable,
when stars are forming

at lower metal counts... Yes.

..it's more probable that these
massive stars are exploding

in that place. So, a supernova
is more likely to occur

where there's less metal density?

Yes, exactly, exactly. Oh.

Which is strange. Yes. Which has not
really been predicted previously.

But it opens up a world of
possibilities... Yes, indeed.

..and a better understanding of the
mechanism of a supernova.

This is just one of the many
scientific discoveries

found using this incredible
facility.

It's time for a changeover,
as the night shift astronomers

get ready to take over
the control room -

but not before taking in
a spectacular sunset.

You've been working here
for ten years now.

Do you ever get bored of it?

No, I mean, cos it's such
a unique place to work.

You know, I live in Santiago,
in a big city of six million people,

and then you come out here,
in the middle of the driest desert

on the Earth. So, to see the sun
setting here every night,

it's still an amazing experience.
Yes!

And I guess it's a precursor,
because we see our local star,

the sun, setting before it opens up
the vista of the universe.

Indeed, exactly. So, the engineers
are getting the telescopes

ready now, then they will pass
those telescopes over

to the operations team at night.

And then we're ready to start
observing galaxies, stars,

all the wonderful things
in the universe.

Now that I've met some of the people
here at the VLT, I want to find out

more about what life is like when
you live and work in a desert,

and who keeps this mini town
running.

This is the Residencia, an oasis
in the desert where the astronomers,

scientists and engineers -
in fact, everybody that keep

the mighty telescopes running -
live.

It is quite impressive.

The architecture is so incredible
that it was even used

as a location in the James Bond
film Quantum of Solace -

and they left behind
their fake rocks.

Oh...

There isn't much natural greenery
here in the desert.

But when you walk inside,

what greets you is a very
different story.

It feels quite tropical in here,
especially compared

to the Martianess desert outside.

But like any good hotel,
it's got all the mod cons,

including a pool. It is amazing.

I want to know more about life
behind the scenes at the Residencia,

so I'm meeting someone who has been
described as the mayor of Paranal,

Vanessa Peidro.

Vanessa, lovely to meet you.

You have a brilliant place here.

It is. It is a fantastic place, yes.

Now, here at the Residencia,
how many people do you cater for

at any one time?

Per day, it's 150 on average. Yes.

So, we have, of course, astronomers,

around ten, 20 astronomers,
and all

engineers, supporting
staff, contractors.

So, as a head of the logistics
and facilities department,

basically, in two words, I try to
make this place run smoothly

and make things work.

Making sure everyone who lives and
works here is well looked after

is a priority for Vanessa
and her team.

There is an expression -
an army marches on its stomach.

Yes. So, how important is food
here at the Residencia?

Food here, it takes a lot of energy,
a lot of people.

We, of course, take into account
the different dietary restrictions

of every single person, of the 150
people that we have every day.

How challenging is it to get
fresh food up to the mountain?

Well, it is challenging.

We have trucks coming usually
twice per week,

and we have to keep everything
fresh.

It is a challenge, but that's why
we have very high technology

and very sophisticated equipments

to keep everything up
to the standards.

With many of the staff working
night shifts,

food is prepared around the clock,
so no-one ever goes hungry.

As well as keeping everyone
fed and watered,

another key part of Vanessa's job
is controlling the lights.

So, we can see the canopy
being deployed now. Yes.

But why is this important?

Well, at night we have to avoid
creating any interference,

any light pollution for
the telescopes.

So, yes, it's definitely...

Not only closing this dome,
the lights,

but also closing the shutters of
the common areas or the rooms.

Having all this light inside
and the green,

it's very important for
the wellbeing.

We have all these plants that create
this warm atmosphere. Yeah.

Because when you look out there,
it does feel like an oasis in here.

So, with the canopy in place,
it really does block out the light.

Exactly. It is...!

Well, it's a very efficient
system, yes. Yes.

Vanessa's team also look after the
leisure activities at Paranal -

to make a home away from home
in the isolated desert.

Ranging from ping pong to swimming,

to music and to photography,

they really offer it all.

The VLT's full potential is
unleashed when the telescopes

work together using a technique
called interferometry.

I'm meeting the physicist in charge,
Dr Francoise Deplancke-Strobele.

Lovely to meet you. And it's
fantastic to be here

on the platform of the VLT.

So, how does interferometry play
a role, and what is interferometry?

It's quite hard to say.

We need interferometry
because astronomers always want

bigger telescope for two reasons.

One is to get more photons.

It's why we have built those
big 8m telescope.

And we are building the future VLT,
which is even bigger. Yes.

But also the resolution.

So, it's not actually about
how much light you get,

but about how big, physically big
your telescope is? Exactly.

So, what we do is to break this
telescope in small pieces,

in smaller telescopes,
that we combine as if they were

part of the same big telescope.
I see.

So, you take the photons that
arrive to your telescopes. Yes.

And they can interfere. They can...

They are friends,
they can work together.

The particularity of the VLT here is
that we combine 8m telescope,

and that nobody can do.

And we form them...

We can also combine them with
a smaller telescope of 1.8m

that can be separated by
up to 200m. Whoa.

So, we reconstruct the image
of a 200m telescope.

Although interferometry is an
incredibly complicated process,

the idea is actually quite simple.

If all the telescopes are pointed at
the same object at the same time,

all the light can be combined
to reveal even sharper details,

like a much bigger telescope would.

Below us are the tunnels that
house the equipment

that make this process happen.

You go first.

So, here we come in the Delay Line
tunnel, where the light is coming

from the telescope, and the light
is then sent to those mirrors

that you see on the big concrete
blocks. Right.

The light is then sent to the
other side of the tunnel,

which is symmetrical from here
on the other side.

It's long. How far down?

It's 120 metres in total.

And then the light arrives on
those kind of carriage

that we have there.

So, the carriage are moving on those
rails that are extremely straight.

So, this is the Delay Line.
But how does the Delay Line work?

The Delay Line makes the photons
wait for their friends.

I see. So, it's like a waiting room
for photons.

It's a waiting room, yes.

Well, some arrive to the first
telescope before the one coming

to the second telescope. Yes.

And to get the interference,
they have to come back exactly

at the same moment in the
instrument. Yes.

The instrument, known as GRAVITY,
has helped make some

ground-breaking observations
since it was installed.

But every time light is reflected
in the Delay Lines,

photons are being lost, meaning
astronomers are missing out

on precious details.

So, the scientists and engineers
at ESO are working on a way

to bring those details into
even sharper focus.

The GRAVITY instrument is going
through a major upgrade

to GRAVITY+.

But the upgrade doesn't extend
just to that instrument.

The upgrade goes through the whole
of the interferometric system

and the adaptive optics system.

The adaptive optics system is
a critical part of the telescope,

because it takes into account
atmospheric turbulence.

It will also increase
the sensitivity

of instruments like GRAVITY.

Adaptive optics enables the images
obtained to be almost as sharp

as those taken in space.

I'm meeting Francoise's colleague,
Dr Frederic Gonte,

who is working on this huge
engineering project.

GRAVITY is a very specific
instrument, because this is an
interferometric instrument,

and they bring the light together
in a single instrument.

But now you're going for GRAVITY+
What is that going to give us?

20 years ago, we used what was
the best at that time.

Now we have really developed the
technology of adaptive optics,

and now we are going to implement
a system with 1,350-plus actuators.

Actuators are components under the
mirror that adapt the surface

to turbulence in the atmosphere
and correct distortions.

Laser guide stars will be added
to each telescope,

with one out of four
already complete.

A laser guide star, the principle is
really to project a laser

on what we call the sodium layer.

When you project this laser,
you excite the sodium

and the sodium will emit some light,

and this light, we detect it as
an artificial star. Yeah.

And using that, we can go
everywhere on the sky,

because then we have always a star
which is bright enough.

You make your own star so
you can monitor it.

We are making our own star,
because we need a lot of light

for this adaptive optics system.

And if you are outside the
galactic plane, the Milky Way,

and you want to observe other
galaxies, then here you have

basically very few stars,
so it is difficult for you

to have the right light.
Laser guide star is there for that.

It's time now to put
the improvements in place,

messy work that is only possible
whilst the mirror is being cleaned.

But I suppose you're limited
because it's the time that it
takes to coat the mirror.

When the mirror is ready to come
back, you need to be out. Exactly.

It's even worse, in fact, because
we have a very short window,

and just after this window, we have
astronomers waiting

for the telescope,
and if we are late... Yes!

..it would be horrible. Not popular!

Much of the work going on behind us
is about the upgrade

to GRAVITY+ -
but it's so much more than that.

It's about an upgrade to
the interferometrics system,

an upgrade to the adaptive optics
system, as well.

And with all these different
technologies coming together,

it's going to lead to an amazingly
cutting-edge system

which is unique to the VLT.

I can't wait to see what
they're going to discover.

I want to learn more about the
science being done here at the VLT.

So, this evening I'm heading
back to the control room.

Dr Abigail Frost is an
ESO astronomer,

and has just started the night
shift.

What's it like sort of living and
working on a telescope like this?

It's a super cool and interesting
job to do.

It involves a lot of shift work.

I mean, I'm based between here and
Santiago, where I do my research.

And so, when I'm here, I'm mostly
observing at night, doing...

..dealing with all these consoles
and all these other instruments.

So, at the moment, we are just doing
some calibrations

with the GRAVITY instrument.

The power of GRAVITY's data
has already been used

to solve a mystery.

In 2020, a team of ESO astronomers
reported the discovery

of the closest black hole to Earth,

located just 1,000 light years away
in the HR 6819 system.

They were looking at a group of
spectral lines and trying to

work out, OK, how are the stars
moving in the system?

If you have these stars in a stellar
system together, you'd expect them

to be moving around each other. Yes.

But they weren't seeing movement
from this star.

They were only seeing movement from
the other star, and that implied

that it's moving quickly around
something else...

Something else, yes.
..which we couldn't see. Aha!

And so, that's why they thought
there was a black hole.

But another group had
a different explanation.

They believed the orbit could be
explained by a binary star system,

two stars orbiting one another.

One of the stars was moving
faster than the other,

not because of something we couldn't
see, but because it was stealing

the other star's mass.

Using the VLTI, Abigail and her
team investigated

which hypothesis was correct.

The VLTI was really like a missing
piece of the puzzle in terms of us

finding out the true origin story.

We had two hypotheses, and we needed
to check what was happening.

And the way that we could do that
is by looking at the distances

between the bright stars. OK.

Because in this scenario, where we
think that one has stolen material,

they have be very, very close
together. Right.

And that's very difficult to
resolve. You need very high

resolution, you need powerful
telescopes, or powerful methods.

And for the other scenario, the
stars would have to be far apart.

Is the mystery solved?
Yes, the mystery is solved.

We got some data with the GRAVITY
instrument, with the VLTI,

and this enabled us to identify
directly where these two stars were.

You don't need a black hole
to explain this system.

Yeah, this mechanism. It's just
a cool case of binary interaction.

Yes!

Stars stealing material from each
other and interacting.

Vampirism! Yes.

An explanation for the results
Abigail and her team found

is the occurrence of a vampire star.

Can you tell me, what is a vampire
star, and should I be worried?

So, a vampire star is essentially
a star that has stolen mass

from another star which
is very close to it.

We often have stars in these binary
systems, and if they're close

enough, they can steal material.

Interferometry was, like, really
the key to cracking the case.

So, that's why I love working with
this technique.

It's super powerful, super useful,

and I want more and more people
to use it.

The VLT is still a world-class
observatory doing

cutting-edge research. But here in
the Atacama, there will soon be

an even more powerful observatory.

The Extremely Large Telescope,
or ELT,

is currently under construction.

When it's constructed in around
five years' time,

the ELT will be the largest
optical telescope in the world.

It's being built about an hour from
the VLT on a mountaintop.

Now, I've spent much of my life
working on large telescopes,

so to see this monster actually
being constructed

is going to be mind-boggling.

When it is finished, the ELT
will be about the size

of a cathedral.

Davide Deiana is one of the
on-site managers.

I've been speaking about this place
for over 18 years,

and so to see it like this, under
construction, is blowing my mind.

This is the biggest telescope
ever built,

with its 39.2m metres in diameter.

We are talking about a major
building that is 60m in diameter,

3m deep, foundation with roughly
9,000 cubic metres of concrete

that have been casted. Wow.

We are talking about the dome
that will be moving,

the rotating mass of the dome,
for example,

we are talking about 6,100 tonnes.

The ELT is being built on top
of a mountain

3,000m above sea level,

providing prime conditions
for observing.

But before they get to that stage,
they have a lot to get done.

So, as we can hear,
we're in a construction site

with things happening all around us.

So, what is happening now? What
stage of the telescope are we at?

OK, so, for the main structures,
we completed the upper foundation.

And for the dome, we are completing
the assembly of the first

skeleton of the dome structure that
is built to sustain...

The cupola that is the enclosure of
the telescope during daytime,

because the telescope must be
at outside temperature

when the door is going to be open.

Yes, I've seen that before on other
telescopes, like Gemini and the VLT.

So, you keep the internal
temperature the same

as the night-time temperature,
so when you open up,

everything is peaceful,
no turbulence. Exactly.

Another key challenge
for this enormous telescope

is earthquake protection for
each one of the 798 segments

that make up the ELT's
primary mirror.

So, basically, they are laying on
top of seismic devices

to survive and to keep operating
when earthquakes are happening.

We have a complex system that
also is a hydraulic control

that allows the disengaging
of these locking devices

when a certain frequency and
with a certain magnitude

is acknowledged, is recorded.

And so, with that hydraulic system,
then the telescope is effectively

floating on that system. Yes.

The engineering behind the
observatory's construction
is fascinating.

But so is what it will be able
to achieve -

allowing in 20 times more light
than a VLT telescope,

so we can see other planets
in more vivid detail.

My journey with telescopes began
when I was about 13 years old,

when I ground and polished
my own telescope mirror.

Now, at that time, the largest
telescope in the world

had a primary mirror of about 4m.

But then along came the stuff
of dreams -

the ELT,
the Extremely Large Telescope.

Here, the primary mirror of the
telescope is 39m in diameter.

I can't wait till it comes online.

It's time for me to leave
the ELT and the VLT.

This trip has been fantastic,
meeting the scientists and engineers

behind the amazing feats that keep
these telescopes cutting-edge.

I'm afraid that's all we've got
time for from here at the ESO VLT.

But do join us next month,

when we'll be having our
Question Time special.

In the meantime, goodnight.