Original subtitles

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.