Original subtitles

Tonight on The Sky At Night, we're doing things

a bit differently.

DOOR CREAKS

Over the years on this programme,

we have investigated all sorts of mysteries -

from sinister black holes lurking in galaxies

to sudden shocks from the early universe.

CROW CAWS

The night sky we all look at is hiding secrets,

only telling us part of the story.

And so tonight, we're going looking for cosmic ghouls

lurking in the shadows.

And where better place to do that than here in Provan Hall -

Glasgow's own medieval and haunted building...

..where strange things have supposedly been seen,

like a man with a dagger

or spooky faces at windows,

or even the ghost of King James V himself?

We'll take the most sophisticated equipment -

that the Sky At Night budget can afford -

and stalk the corridors of Provan Hall to see what can be found.

From mysterious voices of the past

with stories to tell from the darkest parts of the universe...

..to a cosmic ghoul that's still haunting astronomers

decades after it first made its presence felt.

And so, tonight...

We're going ghost hunting.

COSMIC ghost hunting.

BOTH: Welcome to The Sky At Night.

The building behind us

is supposedly one of the most haunted locations in Scotland -

Provan Hall House.

We're told that it harbours several ghosts from its 550-year history.

So, shall we take a look inside, Chris?

Unless you're scared.

I'm not scared! Ghosts aren't real!

To find out what's lurking inside Provan Hall,

we need to look beyond what our eyes can see.

So, I'm going to be listening out for unusual sounds,

while Chris searches for strange movements

with a thermal camera.

See you on the other side.

With any luck. Hmm.

Of course, we're a science programme,

so it's not ghosts we're after -

but finding new ways of sensing what surrounds us in the cosmos

is a large part of the modern astronomer's job.

Take this infrared camera -

paranormal enthusiasts believe it can show them

supernatural shadows, but actually, it's just detecting

light at a wavelength longer than our eyes can see.

Our vision is confined to radiation in a small part of

the electromagnetic spectrum -

the part we call visible light.

But celestial objects give off light in other parts of this spectrum,

like ultraviolet and infrared.

Hang on, what's this?

Hi, Chris! Hiya! How are you?

Of course, I haven't found a ghost.

I've found an astronomer.

Dr Olivia Jones, from the UK Astronomy Technology Centre -

who's recently played a key role in solving a mystery about

an exploding star, known as a supernova.

So, you've been looking at a particular supernova.

Tell us about it.

We've been looking at Supernova 1987a -

which is a supernova that went off in the year 1987.

It was the first time we really got to see the physics

of a star going boom.

When stars explode, their cores collapse.

For more massive stars,

this will create a black hole.

But cores of stars like the one that produced Supernova 1987a

should collapse into an extremely dense ball of neutrons -

a neutron star.

The mystery is, we knew a neutron star was meant to have formed,

and we went looking.

This is the densest material you can find in the universe.

A small teaspoon of this weighs as much as Everest.

We looked in the optical,

we went looking in the ultraviolet

and in the radio.

And we saw nothing.

The best telescopes in the world,

and we couldn't find this neutron star.

A missing neutron star would have meant our theories

about how stars die were wrong.

So, Olivia and her team were very keen to find it.

But there was one thing in their way - dust.

What you have right in the core of 87a is a big pile of dust.

It hides everything from optical light.

It hides all the energetic UV light.

Anything that emits at very short wavelengths

is absorbed by the dust, so you can't see through it.

But the new James Webb Space Telescope - or JWST -

offers something that other telescopes didn't.

It can detect longer, infrared wavelengths

in unprecedented detail.

So, Olivia and her team pointed it at Supernova 1987a

as soon as they could.

This is where JWST comes in. Yes.

JWST is an infrared telescope, and it lets you unveil

and peel back all those layers so you can see right into the core.

So, why is the infrared important here?

The infrared is great cos it lets you see through material.

We've got an infrared camera here.

I pick this up, and there's a handy sheet nearby.

Oh, yes, very good.

If you look with this, with the infrared camera,

you can see my hand. Oh, yeah, really clearly!

And, of course, I can't with visible light.

So, the infrared is able to travel through the sheet. Yes.

The longer wavelength of infrared light lets you see

through material better.

So, if your hand was the centre of 1987a,

the sheet was the dust,

and that was James Webb, this is exactly what we're doing.

Yes!

And the really good news is, we found the neutron star -

which I think is a relief,

because if the neutron star wasn't there,

we would have really had to change physics.

Using data from JWST, Olivia's team were able to find

the signatures of a neutron star at the centre of 87a.

A 37-year-old cosmic mystery

finally solved.

Well, it's a thrilling discovery about a fabulous object.

And keep an eye on it for us. We will do.

For me, finding a neutron star is far more exciting, wondrous,

and, you know, likely... than finding a ghost.

But is a neutron star not a type of cosmic ghost?

A once-bright star still haunting the universe

long after it's ceased to shine?

While infrared telescopes allow us to see parts

of the electromagnetic spectrum that we can't see with our eyes,

we suspect there is a huge part of our universe

that can't be detected by any part of this spectrum.

We call this the dark universe.

Everything that we can see -

the planets, the stars, the galaxies -

they make up just 5% of the universe.

The question is,

why do we think that there's missing stuff out there?

I just got hoked on watching the stars.

A voice from the past is going to help me answer that question.

..got more interested in watching the stars...

Vera Rubin, a pioneer of the study of the dark universe.

So I went to the library, read books,

built a little telescope,

and just decided I wanted to be an astronomer.

I had a physics professor in high school who didn't really know

how to relate to a young girl

who was interested in science.

When I finally went up to him

and told him I was going to college on a scholarship,

he said, "Well, you should do all right

"as long as you stay away from science."

In 1948, despite that atrocious advice,

this woman, Vera Cooper,

graduated from Vassar College.

She was the only astronomy major in her year,

and she was primed and ready to find out more about the universe.

She went on to earn a master's degree and a PhD.

She married and changed her name to Vera Rubin

and became a full-time astronomer.

As a woman in astronomy,

Vera continued to experience inequalities,

but it didn't deter her.

She was denied access to the Palomar Observatory Telescope.

They said they had no ladies' bathrooms.

So, she cut out a skirt-shaped piece of paper,

put it over the male figure on the bathroom door, and said,

"There you go - you've got a ladies!"

Some years later, she made an astounding discovery.

While researching the motion of spiral galaxies,

Vera found something that didn't add up.

In a galaxy, it looks like most of the light is at the centre,

and therefore, we had expected that most of the mass

would be at the centre.

And just like in the solar system,

where most of the mass is at the sun,

you expect that, as things get farther and farther away,

they orbit more slowly.

And what we found is that these stars are going

just as rapidly as those stars,

and we're forced to conclude that they're responding

to a gravitational field we don't see.

And that gravitational field must be composed of dark matter.

Many astronomers were reluctant to accept this conclusion.

But Vera persevered.

She got data from more and more of these spiral galaxies,

and found the same result every time.

Each one needed to have a lot more matter than she could see

to move the way they did.

Eventually, the astronomy community could deny it no longer.

The galaxies and the universe contained unseen matter.

Dark matter.

Sadly, we lost Vera in 2016.

But in many ways, her legacy lives on.

On top of her pioneering research into the dark matter

contained in galaxies,

Vera was also a fierce advocate for women in science.

She was a tireless trailblazer

for astronomers working with children,

as a working mother of four herself.

And her memory also lives on through a ground-breaking

new observatory named after her.

The Vera C Rubin Observatory

has the largest camera ever built for astronomy.

It will help us answer some of the biggest questions

about the universe,

with a key goal in understanding the nature of dark matter.

It might not be ready to take data quite yet,

but the observatory's new camera has already taken this image of

the team that are working on it.

And all those people will be following in the footsteps

of the smart, the daring, the tenacious,

the wonderful Vera Rubin.

What we all dream of is that when you do...

..when you ask questions in science,

when you ask questions of nature,

you will get answers that are much bigger than

what you went out to find.

Analysing the movements of stars and galaxies

has provided evidence that dark matter exists -

but how do we actually go about finding it?

Dark matter expert Professor Chamkaur Ghag is going deep

underground in Yorkshire...

..to find out how UK scientists have been searching

for elusive, ghostly dark matter particles.

Over a kilometre beneath me is one of the most

incredible labs in the UK -

the Boulby Underground Laboratory.

And deep in this working salt and polyhalite mine,

scientists are trying to detect particles that have just

passed through the ground completely undisturbed,

like ghosts moving through walls.

In the 1990s, scientists realised that Boulby was a perfect location

for conducting research into dark matter.

Hey - good to go.

This far underground,

cosmic radiation is reduced by a factor of a million,

making it easier to spot particles

that normally pass through undetected.

Good evening. I'm in a most unusual setting.

Patrick Moore and the Sky At Night team also visited Boulby

20 years ago.

But back then, the lab was a much smaller operation.

Here I am, in a lift going three quarters of a mile underground

in Boulby Mine, towards this strange observatory.

One thing that hasn't changed in the last 20 years

is the seven-minute lift ride down into the mine.

So, we've just got into the cage.

We're still up on the surface, but it's...

We've just started moving now.

The next time we get out of this,

we'll be deep, er, in the earth.

Boulby is now the site of a vast range of ground-breaking research

beyond dark matter -

including astrobiology studies into deep subsurface microbial life,

testing of planetary rovers

and other technology developments for planetary exploration.

But I'm really here for those ghostly particles -

just like Patrick in 2004.

What experiments have you got running down here?

The ZEPLIN detector behind you is a liquid xenon detector.

This detector, called ZEPLIN,

was looking for theoretical dark matter particles called WIMPs -

weakly interacting massive particles.

It contained liquid xenon,

which is great for detecting radiation because it gives off

flashes of light when particles collide with it.

The hope was, if this liquid xenon was brought underground

where most other radiation from space couldn't reach,

it would be possible to pick out a collision between

a xenon particle and a WIMP.

And, although ZEPLIN didn't find a dark matter particle,

that liquid xenon technology went on to be used in dark matter detectors

around the world,

including an experiment called LUX-ZEPLIN - or LZ -

currently the world's most sensitive dark matter detector.

I'm meeting facility manager Emma Meehan to learn more.

So, can you tell us about, you know,

how you found yourself at Boulby? It's an amazing story. Yeah.

I had a friend who worked here who called me and said,

"Does your mum want a job?

"It's two days a week coming underground to clean

"in this underground lab."

And I said, "My mum won't work in the mine.

"But tell me about it. Maybe I can take it."

And then I got the job.

And at lunch breaks, we would sit down,

and I would sit with all of the academics,

and we would start to have chats about physics.

So, I started to learn. I decided to study with the Open University.

And I started to kind of throw myself in the way of scientists,

saying, "What are you doing? Can I help you do this?"

In just eight years, Emma went from cleaning the lab two days a week

to being their senior science technician.

She also helped to develop this lab - BUGS -

which has a key role to play in the search for dark matter.

BUGS stands for Boulby Underground Screening.

And what that means is that we look at materials here

in terms of their radioactive content.

Every little bit of radiation can swamp the detector with noise,

so when we're building these detectors,

we care about the materials that we build them out of.

We want to check how radioactive they are.

There's the LZ experiment that's operating right now.

And these detectors played a pretty important part in that, right?

Right, yes. What were they doing?

So, we screened an awful lot of the electronic eyes,

the photomultiplier tubes.

These electronic eyes are extremely important.

They are the part of the detector that will confirm that

a dark matter particle has passed through the liquid xenon.

What we know, Cham, is that we're never going to see

the dark matter particle.

We're only ever going to see its interaction.

What that would look like, in the terms of this liquid xenon,

is that the particle would pass through,

it would hit a nucleus of the liquid xenon,

which would recoil.

Dark matter will disappear off, gone.

But that recoil will create a lovely flash of light in that xenon.

But these photons are picked up

by these incredibly sensitive electronic eyes.

If a detection is made,

it would transform our understanding of the cosmos.

And it would be a very special moment for Emma.

So, if dark matter is detected in LZ, what I know, Cham,

is that I held the thing that is going to see dark matter

for the first time.

But even if dark matter is not found at LZ,

the search for these elusive particles will not stop there.

The BUGS lab is now being used to screen possible materials

for use in a new, bigger, more sensitive detector

called XLZD.

And so you'll be screening materials and shipping them where?

Where's XLZD?

Well, what we know is that there's only very few places in the world

where it could be.

And here at Boulby...is a strong contender as one of those.

Well, thank you so much, Emma. It's been, you know, great to learn

more about what's going on here and all the work

that you and everyone here at Boulby have been doing. Thanks, Cham.

Even as someone who's worked on dark matter for most of their life,

I'm still awestruck by the work that goes on down here at Boulby Mine.

And it's easy to question why we'd spend so long

and so much effort

looking for something that, you know, we can't even see.

But it's mind-blowing to think that, with just a few pings

in a xenon detector, we could understand

one of the greatest mysteries in the universe.

And I, for one, am looking forward to a ping.

Mysterious dark matter is enough to give astronomers nightmares.

But black holes are the true monsters of the cosmos,

hidden out there in the dark.

And in the past decade,

scientists have found a clever new way to track them down.

Light - it's how we see everything around us.

It's how we find our way, how we notice the people we love

and how we recognise ourselves in the mirror.

But just as there are other ways for us to comprehend

the universe around us -

like hearing, listening to sound waves -

there are other types of information that we can pick up

from the universe.

Like gravitational waves - ripples in the fabric of space itself -

which can reveal cosmic events

that otherwise we'd never be able to see.

Oh, Tessa! There you are!

How are you?

Good, thank you!

Professor Tessa Baker, from the University of Portsmouth's

Institute of Cosmology and Gravitation,

is at Provan Hall to tell me more.

One of the most exciting things is that we no longer just need to look

at the universe in the light. We can use other methods.

So, tell us what you've been up to with gravitational waves.

So, we have a network of detectors all over the Earth.

And these work together to detect

gravitational waves, these tiny, tiny ripples from merging

black holes and exotic stars.

Most of the time, gravitational waves are too small

to be detectable.

But when two dense objects like black holes or neutron stars merge,

they send gravitational shock waves out across the universe.

We get these ripples,

these gravitational waves spreading out through the universe.

How on earth do you detect them?

You need a gravitational wave detector.

And that's made of two really long laser beams.

Our current ones are about four kilometres long,

and they meet at right angles.

When a wave comes through,

it will change the lengths of those two arms,

so it'll make one a little bit shorter

and make one a little bit longer.

And when we bring those laser beams back together,

we can tell that's happened.

But the change is really small, right?

Yeah, absolutely.

Smaller than the size of an atom.

The properties of the gravitational waves we detect -

their durations and frequencies -

tell us about the speed and mass of those merging black holes

and neutron stars.

And it's possible to bring those properties to life

through sound.

So, one of the cool things about gravitational waves is

we can actually convert them into audio files that you can hear.

OK. So, let's, erm, show some examples of this.

And I should stress gravitational waves don't actually make a sound,

but it's just like converting radio waves into sound. Right, OK.

So here is the first gravitational wave we ever detected.

SOFT BLIP

OK, I can hear that.

I was expecting something a bit more spectacular, I have to say.

So, it's very short, right?

And it's at a pitch which is quite hard for the human ear to hear.

And that's just because things are happening fast, right?

These black holes are spiralling around each other really quickly.

Yeah. But remember, we said that neutron stars can also merge

and make gravitational waves. Right.

And because they're lighter,

they produce an even... even stranger sound.

So, here is the sound of that binary neutron star event

we detected in 2017.

LOW HUM INCREASES

BLOOP

Well it's a proper "whoop" at the end. Right.

The sound is much longer.

And again, that's just to do with the neutron stars being lighter,

so they're in the sensitive range of the detectors for longer.

So, you do hear it for longer?

Yeah.

These gravitational waves are already revealing unseen parts

of the universe.

But to learn more, we need to detect new types of events

that produce waves of different wavelengths.

For that, we need new detectors.

And there's one particularly ambitious project,

the Laser Interferometer Space Antenna - or LISA -

which is taking gravitational wave detection into space.

Tell us a bit about LISA

and what it's going to see that we can't see otherwise.

So, LISA is going to be a triangle of detectors in space.

So, these three detectors fly around,

and they have laser beams between them.

So, it's like what we have on the ground,

but all in space without supporting infrastructure.

And presumably, they're quite a long way apart as well.

2.5 million kilometres.

Oh, wow, OK. Huge!

And the reason we want the arms to be that long is that allows us

to pick up gravitational waves that have really long wavelengths.

So, at the moment, we're seeing things that are 10, 20 times

the mass of the sun.

These black holes that LISA will pick up

are maybe a million to 100 million times the mass of the sun.

So, they're the ones that live in the middle of galaxies, right?

Right. It's going to be so exciting.

I know we've got to wait, and you're keeping us entertained

in the meantime, but thank you very much for telling us

about gravitational waves. Come back soon.

Thanks, Chris.

Hearing those sounds produced by ripples in spacetime

is kind of breathtaking.

Gravitational waves allow us to access

this unseen, but really important, part of our universe.

Cosmic events on the grandest of scales

detected down here by the tiniest change in the movement of light

hitting a mirror.

Now, Pete is at the Bedford School Observatory

to tell us how to spot another hidden object in the night sky.

We're all used to looking at bright objects in the night sky -

moons, planets, stars, comets, meteors.

But the absence of light can also help reveal

some rather ghostly-looking objects,

which are known as dark nebulae.

Dark nebulae are interstellar clouds that are so cold

and full of dust that they block out all visible light.

These spooky black clouds are important spawning grounds

for new stars and planets.

So, with dark nebulae, there's something for everyone -

whether you have an observatory like this,

or whether you're just outside looking up at the night sky

without any equipment.

As the skies start to darken after the June solstice,

it's a good time to start looking for dark nebulae.

One prime location is near the constellation Aquila, the Eagle.

First, identify the large prominent asterism

known as the Summer Triangle -

made up of the stars Deneb in Cygnus, Vega in Lyra

and Altair in Aquila.

Just northwest of Altair

are two dark nebulae

silhouetted against the rich background starfield.

Together, they look like a capital E

and are known as Barnard's E

after Edward Emerson Barnard,

a gifted observational astronomer

who compiled a catalogue of dark nebulae.

Other summer examples include the Pipe Nebula, in Ophiuchus,

to the east of the bright red supergiant star

Antares, in Scorpius.

Another smaller example

sits near the bowl of the pipe

and is known as the Snake Nebula.

If you live in a dark sky region

and can see the Milky Way passing through Cygnus,

with just your eyes, look out for where it splits

due to a region of dark gas and dust.

This is the Cygnus Rift.

And the region to the north of it,

near the bright star Deneb,

is a dark nebula known as

the Northern Coalsack.

To get a good image of a dark nebula,

you need relatively dark skies -

so, probably best to wait for

the effects of the June solstice to wear off -

and also, to have the moon out of the way.

A mid- or wide-angle lens is good for capturing large areas of

the Milky Way,

which will show bright star fields

and dark dust lanes.

As ever, if you get any photos, we'd love to see them,

so do upload them to the Sky At Night Flickr.

Now, there was an amazing display of the northern lights,

which was visible across the UK in early May.

And Sky At Night viewers got some incredible photos.

When you're looking out for

all those amazing objects in the night sky,

don't forget to think about those that you can't see.

Because in the galaxies, the dust and the darkness,

cosmic ghosts are lurking.

Each with an incredible story to tell us about our universe.

BOTH: Goodnight. SHE CHUCKLES