Original subtitles

Our universe is a place of infinite variety.

Two trillion galaxies...

..billions and billions of stars...

..and countless planets, worlds beyond imagination.

The universe is so vast, so incomprehensible, so terrifying,

that I think it's quite natural for us to choose to live out our lives

completely oblivious to it.

Perhaps that's why there's a sense of relief that rises with the dawn.

The brightening sky hides the stars and the questions that they pose.

After all, they are the biggest questions.

How did the universe come to be?

Why are we here?

And how will it all end?

We have to face those questions if we're ever to acquire

a truly deep understanding of ourselves.

You see, astronomy challenges us.

From one perspective, we're just grains of sand adrift

in an infinite and indifferent ocean.

But from another perspective, we are nature's most magnificent creation,

collections of atoms that can think and wonder about the universe

and choose to explore it.

OVERLAPPING LAUNCH COUNTDOWNS

We have liftoff... Zero...

In our quest for answers, we're venturing ever further from home,

far beyond the planets...

..and out to the stars.

Our spacecraft are sending back a stream

of extraordinary revelations...

..visions of alien worlds...

..with the ingredients to create life.

We've seen galaxies collide...

..black holes devouring star systems...

..and we may have glimpsed the origin of the cosmos itself.

With every new observation, every new piece of knowledge,

there is the opportunity to acquire a deeper understanding.

And as we answer question after question, we get ever closer

to being able to tell what is surely the greatest story ever told.

# Take me away. #

Nasa's Parker Solar Probe, a daring mission to shed light...

..on the mysteries of our closest star.

This is a journey into never-never-land, you might say.

Nasa's Parker Solar Probe is the first spacecraft to touch a star.

It's designed to fly through the sun's atmosphere...

..braving temperatures no spacecraft has ever endured.

The Parker Solar Probe is allowing us to know our star

as we've never known it before.

And it's also helping us to tell the story of all the stars.

Our sun is from a long line of stars dating back to the dawn of time...

..from fierce blue giants...

..which first lit up the universe...

..to later generations...

..whose deaths enriched the cosmos with precious elements...

..the building blocks of our solar system...

..and allowed our sun to create the thing

which brings meaning to the cosmos...

..life, you and me.

We have a strange relationship with the stars,

somewhere between awe and indifference.

I think we take our star, the sun, for granted,

partly because of its predictability.

Every day, it rises in the east and sets in the west...

..without any help or reverence from us.

But many ancient cultures deified the sun.

They treated it as a god.

And the sun gods were creators and destroyers of worlds.

So which is it?

Well, I think that the modern story of the stars, as told by science,

which is indisputably an epic story,

stretching back over 13 billion years to the origin of the universe,

places them firmly in the realm of the gods.

If we want to understand where these gods came from...

..we have to go back...

..to a time before the stars.

In the beginning, the universe was dark.

But it was not empty.

Something was lurking in the void...

..stretching out tendrils.

The cosmic web grew to become a vast structure...

..crisscrossing the entire universe.

It was formed by interlocking filaments of dark matter.

And it was at the places where these filaments met...

..the intersections...

..that the first stars, our sun's earliest ancestors, were born.

The cosmic web is the scaffolding of the universe,

the vast and intricate structure that spans the void.

The web is made primarily out of dark matter,

a mysterious substance that dominates the universe,

although we don't know what it is.

It's one of the great mysteries in modern physics.

It's probably some kind of particle

that interacts very weakly with itself and with light.

It doesn't interact with light.

You can't see it, which is why it's called dark matter.

But it does influence the universe through its gravity.

It was in the dark heart of the cosmic web

that gravity began to sculpt the early universe...

..drawing together the two simplest elements - hydrogen and helium...

..the raw material for the very first stars.

Hydrogen gas clings to the filaments of the web,

attracted there by the gravitational pull of the dark matter.

And where those filaments cross, the gas can become dense enough

to collapse under its own gravity to form great clusters of galaxies,

each filled with billions of stars.

The universe was approaching a turning point.

Hydrogen and helium poured into the regions

where the filaments crossed...

..gathering into ever denser clouds.

Gravity asserted its grip...

..and the clouds of gas began to collapse...

..becoming denser and denser.

And in the densest regions, the gas became so hot...

..that nuclear fusion reactions began.

And out of the maelstrom...

..the first gods emerged.

And there was light.

The stars illuminate the universe.

But that is the least interesting thing that they do.

The thing that makes the universe interesting,

that brings meaning to the universe is that -

life, you and me.

And life is just chemistry.

And chemistry requires complex chemical elements.

The only thing that existed in the universe before the stars

was hydrogen and helium.

Life requires carbon and oxygen and iron.

All those things were made in a process called nuclear fusion,

in the cores of stars or even, for the heavier elements like gold,

in the collisions of stars.

So, without the stars, the universe would be uninteresting.

It would be meaningless.

It would be just an infinite box of gas.

The first stars were monsters...

..hundreds of times as massive as our sun.

They burnt with such ferocity that they shone blue...

..with surface temperatures in excess of 100,000 degrees.

They were the largest stars ever to have lived...

..violent and volatile giants.

A star is essentially a balancing act.

The force of gravity is constantly trying to collapse it,

and that pushes its ingredients - primarily hydrogen, single protons -

closer and closer together.

Now, when those protons get close enough together,

another of the fundamental forces of nature, the strong nuclear force,

takes over and it can stick the protons together.

That releases energy, which creates a pressure which holds the star up.

Now, the more massive the star, the stronger the inward pull of gravity,

and the more energy has to be released to maintain the balance,

and so the faster the ingredients are used up.

..fighting the relentless pull of gravity...

..consuming more and more hydrogen fuel

to maintain their precarious equilibrium.

For most of its life, a star burns hydrogen -

the simplest chemical element, with one proton in its nucleus -

into helium, with two protons.

Now, when it runs out of hydrogen in the core,

the core starts to collapse and heat up,

and the star responds by building ever more complex elements.

So it makes carbon, with six protons,

and oxygen, with eight protons,

releasing more and more energy as it goes.

But when the star has assembled iron in its core,

with 26 protons in its nucleus,

no more energy can be released.

The star loses its battle against gravity.

It collapses

and in a final moment of creation,

salvaged, if you like, from its destruction,

it distributes those newly minted heavy chemical elements

out into the universe.

Imagine we could journey back in time

and watch the first star live out its brief, luminous life.

After only a million years,

the star used up all of its fuel...

..the core collapsed...

..the star imploded...

..and then rebounded in a colossal explosion -

a supernova.

In death, the first stars began to transform the cosmos,

enriching the ocean of hydrogen and helium,

which filled the universe with heavy elements,

to build new generations of more complex stars.

Over time, these elements gathered together...

..creating rich clouds of gas and dust.

Nurseries where new generations of stars were born.

And not just stars, but families of stars -

the first galaxies.

And around this time,

some of the early star systems formed

in our own galaxy, the Milky Way.

A new age of complexity was dawning in the universe.

Now there were stars of different sizes...

..and different colours...

..and, crucially, new bodies had appeared...

..planets.

Places where the rich chemical elements

built by previous generations of stars could finally find a home.

Countless billions of stars have come and gone

since those first giants illuminated the darkness,

each enriching the universe with the material

out of which the next generation formed.

Blue stars and white stars, single stars,

double stars, even triple star systems orbiting around each other.

The conditions were now right for those stars to drive the universe

into a new and profound age of complexity.

Our Sun was formed from the ashes of generations of ancestors.

Just one small star in a galaxy of billions of brilliant gods.

For the first million years of its life,

the Sun was virtually alone,

wreathed in clouds of gas and dust.

The dust slowly clumped together...

..forming clusters, the size of pebbles,

then boulders...

..and finally...

..planets.

But the planets were lifeless rocks.

Only the Sun had the power to turn them into worlds.

Some were too far away from the Sun.

Ice giants -

frozen, seemingly, into infertility.

Others formed too close to the Sun,

seared by a relentless light.

They became scorched desert worlds,

but there was a planet in the Sun's family

that quite by chance formed neither too close nor too far away.

An arcadia, where our star could breathe life into dust.

The planets are just the leftovers from the formation of stars.

The sort of debris, if you like.

It's just little specks orbiting around those magnificent flames,

but the planets are also the places in the universe

where gravity has concentrated the heavy elements

built by previous generations of stars.

And that makes the planets the canvas

on which the stars can create.

The canvas on which the stars can create,

what do I mean by that?

Well, just look around.

Everywhere you look on Earth, there is complexity.

Not only mountains and rivers,

but living things, animals and plants, human beings,

human civilisation,

the most complex thing we know of anywhere in the universe.

So you have to ask yourself, how can it be that such complexity

can emerge completely naturally in the universe?

Well, the answer, in fact, was known in the 19th century,

and it comes from the science of thermodynamics.

In the 19th century,

people were interested in the efficiency of steam engines,

and steam engines are, after all, the machines that powered

the factories that allowed people to build increasingly complex things.

And it turns out that the only thing that matters for a steam engine,

the thing that determines its efficiency,

the thing that allows it to do work and build things

is the temperature difference between the fire,

the furnace and the heart of the steam engine

and the cold environment surrounding it.

In the universe, the stars are hot spots in a cold sky.

We are sitting, in a very real sense,

inside a giant steam engine, powered by the furnace of the Sun.

And it's in that sense that the stars are the creators

of complexity in the universe.

But creating complexity is a subtle art.

You need an engine -

in this case, a star that's not too wild and flashy.

A star which is consistent enough for long enough

to kindle the sparks of life...

..and allow those sparks to flicker and flourish.

The most important property of a star,

if it's to nurture a civilisation,

is magnificent dependability.

No-one knows exactly how life on Earth emerged...

..but what we do know is that at some point,

primitive cells living in the ocean began using the Sun's energy

to power life-giving chemical reactions.

These cells formed a bridge between Earth and Sun,

delicate engines which harness the fires of our star,

using sunlight to turn carbon dioxide and water into food.

This process, known as photosynthesis,

unleashed the Sun's creative power...

..and drove the evolution of complexity...

..from primitive bacteria,

to plants and trees...

..and, ultimately,

to you and me.

Photosynthesis is a process that's very easy to describe in words.

The plants take energy from the Sun

then use it to react carbon dioxide and water together

to make sugars and a waste product, oxygen.

Really easy to say.

Very difficult to do.

I mean, there's a part of that photosynthetic machinery,

everything you see here,

every plant on the planet's got a photosystem, too.

It's comprised of 46,630 atoms,

all working together in an intricate machine.

Very efficient. It took billions of years of evolution.

Then we eat the plants, or we eat something that's eaten the plants

and we do the reverse reaction.

We take those sugars and we breathe in that waste product, oxygen,

react them together, release a bit of energy,

a bit of the stored sunlight, if you like,

and we use that energy to maintain our structure,

to grow, to live.

Trillions of stars have existed since the universe began...

..but ours has nurtured that most miraculous thing,

life.

And that makes the Sun a truly remarkable star.

That is the only star we know of

anywhere where there are collections of atoms in orbits around it,

you and me,

that have named it.

The Sun, our Sun.

We've worshipped it, deified it since the dawn of history.

In fact, it's been argued that the Sun lies at the foundation

of all religion, and there may be some truth in that.

In fact, I think there is a deep truth in that,

because we all owe our existence,

this brief time we have in the universe,

to that star.

In fact, in a deeper sense, to all the stars.

We don't need to invent imaginary gods to explain the universe.

We can replace them with the real thing.

Everyone we love...

..everything we value...

..our supreme accomplishments as a civilisation...

..were created and crafted...

..by stars.

There are over 200 billion stars in our galaxy...

..and there are two trillion galaxies in the observable universe.

We're living in the Age of Stars...

..an era of light and life in the cosmos.

From our fleeting human perspective, stars seem eternal...

..but even gods are not immortal.

Where there is light,

there is darkness.

Stars are creators...

..but they can be jealous guardians of their creations.

Many smaller stars don't die in spectacular explosions,

instead, they slowly. fade away.

They hang on to the precious elements they made,

becoming fossil stars...

..and as more fossils litter the universe,

more life-giving elements remain locked away,

starving the cosmos of the material needed

to make new generations of stars.

The Age of Stars may seem infinite,

but it had a beginning

and it will also have an end.

Imagine a timeline of the universe

and imagine that this is the origin of the universe,

the Big Bang, 13.8 billion years ago.

After 100 million years or so, the first stars formed.

On this scale, one centimetre is about 20 million years.

After four billion years, the peak rate of star formation occurred.

The maximum number of new stars were born.

After nine billion years,

our Sun was born.

And today we stand,

13.8 billion years later,

about halfway through the lifetime of our Sun.

Now, in about five billion years' time,

our Sun will die, but new stars will be born

and many of the oldest stars in the universe,

the smallest stars, will continue to shine.

In fact, we think that the last star will cease to shine,

the universe will go dark,

in around ten trillion years.

On this scale, that's about 5,000 metres away from the Big Bang.

But that's not the end of the universe.

As far as we know, the universe will continue expanding forever.

And so the Age of Starlight is the briefest moment of time

in the infinite history of the universe.

The Age of Darkness will go on and on and on.

Stars won't just disappear, of course.

They'll be here for aeons to come.

But over time, the universe, will grow darker,

colder and emptier.

There are stars around today that existed

close to the beginning of the Age of Stars...

..and some of them will also witness the end.

They're the longest lived stars in the universe,

red dwarfs.

TRAPPIST-1 is one of these ancients.

It's already more than seven billion years old,

almost twice as old as our Sun...

..but only around a tenth of the size...

..and less than 1% as bright.

It's a cool star, slow-burning...

..and that is the secret of its longevity.

Because they burn slowly,

red dwarfs live for a very long time...

..far longer than any other star.

Like the Sun, TRAPPIST-1 has its own planets -

seven rocky worlds,

each roughly the size of Earth.

Some may have atmospheres

and even oceans...

..but there the similarity ends...

..because these are strange worlds.

Every one of these planets is locked in its orbit,

one side facing TRAPPIST-1,

the other side frozen,

permanently exposed to the cold void of space.

If you could stand on the surface of one of these ancient worlds...

..as the aeons passed...

..you could watch the future of the cosmos slowly unfold.

And one day, five billion years from now,

you'd see our Sun flicker and fade away forever.

The death of our Sun will probably go unremarked.

We had hope that we'll be around to see it.

Maybe some alien astronomer on a world far away

across the Milky Way will see it through the end of their telescope,

but I don't think they'll give it a second thought.

We've seen hundreds of stars die

and we don't give them a second thought.

But I think the death of our Sun will matter here locally

in this little corner of the galaxy,

because it will mark the end of a glorious time

in the history of our galaxy,

where meaning, where science and literature

and art and poetry and music existed here.

And that does matter.

Why does meaning have to be eternal?

It's the fragility of our lives that makes them valuable.

I think the wonderful thing is that our star

has taken the laws of nature here on this planet

and crafted such a magnificent expression of them.

You, me and all this.

Stars like TRAPPIST-1 will linger on long after the death of our Sun.

We will never know the name of the last star...

..but we know that the last star to shine...

..will be a red dwarf.

The last star will slowly cool

and fade away.

With its passing, the universe will become, once again,

a void,

without light

or life

or meaning.

The stars illuminate the universe

and create its most intricate structures,

and one day they will all be gone.

The stars are gods, but they are mortal gods.

And when that time comes when the last stars have faded

and all possibility of life and meaning in the universe

has faded with them,

they will have left the most profound legacy

because for a moment in the long history of the universe,

the stars illuminated the dark

and allowed us to illuminate it, too.

MUSIC: Who Knows Where The Time Goes? by Fairport Convention

# For who knows where the time goes?

# Who knows where the time goes? #

We want to study the Sun because it teaches us a lot about stars.

It teaches us a lot about all the other millions and billions

of stars in our galaxy and beyond.

There was a moment when we were putting the spacecraft together

that I just took a moment and looked at the spacecraft

and realised this is going into a star.

And to realise how special it was

to be able to have worked on this

and that humanity decided this was something we wanted to do.

Status check.

Go, Delta. Go, PSP.

Minus 15.

Launch night, I was sick to my stomach.

Five, four, three,

two, one,

zero.

Liftoff of the mighty Delta IV Heavy rocket

with Nasa's Parker Solar Probe.

There we go.

The spacecraft is the first that NASA has named after a living

person because Eugene Parker is really such, you know,

an eminent physicist in our field.

The Delta IV Heavy is a very slow rocket

compared to the other launches I've seen,

so I just saw fireballs and was very, very frightened for a while.

25 seconds into flight.

Temp pressures continue to look good on all three boosters.

Then realising that this was all OK,

as it slowly made its way up into the sky.

Now, 50 seconds into flight.

Parker Solar Probe is so revolutionary

because it's the first time that we're actually going in

to touch the Sun.

We're going 94% of the way from the Earth to the Sun

to actually experience the solar corona, the Sun's atmosphere.

I think at closest approach,

it'll be about eight solar radii from the Sun,

which is just mind-blowingly close.

So we were expecting things to be very hot,

over 2,500 Fahrenheit,

but in a soup of a million degree plasma.

That's a real challenge for the spacecraft

to survive that environment.

So in order to do that, there's a very large heat shield

on the front of the spacecraft,

which protects the majority of the instruments

which are sat behind on the spacecraft body.

What makes Parker so great is the fact that it has a set

of instruments that work together in order to look in all directions,

in order to solve those big mysteries about the solar wind.

The solar corona has been mysterious to us since we've known about it,

so it's a very strange thing.

The surface of the Sun is sort of 6,000 degrees,

and then above that, you have this very thin atmosphere

that's a million degrees, super hot.

And the way that's heated, we know it has something to do

with magnetic fields, but we don't know exactly how it works.

That's where the solar wind is generated.

We don't know quite exactly how that works, either.

Other things that have come out of this are coronal mass ejections.

When we originally did the proposal,

we were thinking that we would see five

in the entire seven year mission, if we were lucky.

We ended up seeing around four to five in the first year,

so there has been just a total switch

in terms of how active the Sun is

or what we classify as coronal mass ejections.

Maybe a little bit of both.

It is a joy to see all the data coming back.

It's a joy to share it with others

and to see them be as curious as I have been for the last decade.

So Parker's just begun its mission, really,

and it's already really started to truly transform our understanding

for how the Sun works.

Next time...

..we had deeper into the galaxy...

..on the hunt for alien worlds...

..and perhaps the first signs of life.

Journey through the universe with the Open University

and learn more about stars, planets and galaxies with this free poster.

Order your poster by calling...

Or go to...

and follow the links to the Open University.

MUSIC: Who Knows Where The Time Goes? by Fairport Convention

At this precise moment on a planet far, far away...

..an alien sunrise ushers in a new day.

But will alien eyes gaze upon it?

Or will it go unseen?

Just another moment in a vast, sterile universe?

The hunt is on for the answer.

Magnificent desolation.

Beautiful, beautiful! Ain't that something?

# Take me away. #

The Milky Way...

..hundreds of billions of stars...

..spread across 100,000 light-years of space.

Among them, the sun...

..with eight planets orbiting around it, including our home.

Until very recently, these were the only worlds we knew of,

the only planets we could hope to explore

for signs of life beyond Earth.

When I first got into astronomy back in the 1970s,

we knew of no planets beyond our Solar System.

We didn't have the technology to detect them

even if they were there.

Our neighbourhood was the only place we could look for life.

And so the hunt for life began in our own backyard.

Over the last few decades,

multiple missions have explored our Solar System's planets...

..and even some of their moons.

But to date, even as we continue to look, no convincing evidence of life

has been found on any of these worlds.

Earth remains one of a kind...

..the only living world around the sun.

But as the exploration of the Solar System continued,

another search had begun...

...for worlds that lie far beyond these shores.

You know, the wonderful thing about astronomy is that

as we develop better and better technology

and accumulate more and more knowledge about our universe,

we turn more and more of these points of light in the sky

into worlds.

I mean, that, we've known is a world for a long time

because that is the planet Mars.

But just above Mars tonight is a constellation called Pegasus.

This is the Square of Pegasus.

And we now know that around there is a star called 51 Pegasi,

which has a planet orbiting around it,

a gas giant about the size of Jupiter

that goes round that faint point of light every four days.

It is wonderful to think that in my lifetime -

in fact, in my adult lifetime, in the last 25 years -

we've gone from a universe

that could have been devoid of planets beyond our Solar System

to a universe that we know is teeming with places

that we can search for life.

Over the last three decades, some of the most powerful telescopes

on Earth have joined the hunt...

..searching for planets unimaginably far away...

..hiding in the dark.

Planets like 51 Pegasi b...

..the first world outside our Solar System to be detected

around a sunlike star.

51 Pegasi b is a gas giant, around half the mass of Jupiter...

..but far closer to its star.

Just imagine what that world might be like...

..a world with skies torn by titanic winds...

..where its hot interior is bathed in rain of sapphires.

In every sense, 51 Pegasi b is an alien world.

And we soon discovered that the galaxy is full of planets

unlike anything seen in our Solar System...

..planets enveloped by fierce radiation...

..their surfaces battered and stripped

by the high-energy strobing light of their star...

..worlds so cold, their atmospheres have frozen solid...

..or great swollen planets...

..with the density of Styrofoam...

..and fathomless atmospheres.

These discoveries proved that, in one sense, we really are not alone.

There are other worlds out there waiting to be explored.

We estimate that in the Milky Way galaxy,

there are more planets than stars - hundreds of billions of them.

That's hundreds of billions of places to look for life.

But there's a catch, because not all worlds - by a long stretch -

are like this one.

The first planets we found appeared too bizarre, too large

and often too close to their stars for living things to survive.

To find worlds where life could exist, we needed to look for

smaller, rocky planets in orbits further from their stars.

MISSION CONTROL: T-minus 10, 9, 8, 7...

We needed to look for another Earth...

..3, 2...

Engine start. 1, 0, and liftoff of the Delta II rocket with Kepler,

on a search for planets in some way like our own.

..so the hunt moved to space

with the launch of Nasa's Kepler Space Telescope...

And we have separation.

..searching for Earth-like worlds in the galaxy beyond.

Kepler crossed 94 million miles of space...

..until it arrived in a steady orbit around the sun...

..from where it looked out with a fixed and clear gaze...

..to a single patch of sky in the constellation of Cygnus.

Exposing its sensitive light meter...

..to the light of 150,000 stars...

..it began to look for Earth-like alien worlds.

Kepler doesn't detect planets directly. They are far too small.

They're just specks of dust relative to their parent star.

They're also very faint.

They don't emit light of their own, so they just glow very dimly

in the reflected ambient light of their stars.

So, Kepler has to detect planets indirectly.

Imagine that a moth just flew across the beam of light

from the lighthouse. Now, I wouldn't see the moth,

but if I had a sensitive enough detector

and everything was lined up properly,

I might just see the brightness of the light dim.

And that is how Kepler detects planets.

We imagine there's an alien astronomer

in some distant solar system looking back at the sun,

and everything's lined up so they see the Earth

trace across the face of our star.

They would see the light from the sun dim by one-hundredth of 1%.

It's a tiny amount, but it's enough.

And if they saw that dimming was regular,

if they saw the star dim once every year, in this case,

then they would infer that there's a planet orbiting around a star.

With its exquisitely sensitive light meter...

..Kepler sees only the regular dimming of pixels...

..just a few bits of information.

But from those bits, astronomers can begin to build a picture

of the worlds that dim the starlight...

..worlds that might, in some way, resemble our own...

..worlds like Kepler-36b.

The planet was one of Kepler's earliest discoveries.

Orbiting a star similar to our own,

we'd found a world that, at first glance, might seem familiar.

Weighing in at around four times the mass of our own planet,

Kepler-36b was one of the first of a new class of planet -

a super-earth.

The Kepler data doesn't just allow us to say there's a planet

around that star. It allows us to characterise those planets.

So by looking at the precise way that the light fades

and then rises again, and the timing between the dips,

we can measure the orbits of the planets.

And if there are multiple planets in the system,

we can even estimate their masses,

so the Kepler data allows astronomers to paint a picture

of the worlds it discovers.

But the more detailed our picture of Kepler-36b became...

..the less Earth-like this super-earth appeared to be.

It orbits very close to its star, circling once every 14 days.

And it has company...

..a gigantic gaseous companion...

..with an albeit unusually close to its smaller sibling.

The proximity of both its star and sister planet

allows us to imagine the bizarre conditions

that may exist on the surface of Kepler-36b.

The planet may be tidally locked,

which would mean that one hemisphere always faces the star.

On this side, the punishing heat could turn the ground molten...

..creating rivers of lava that would crisscross the surface.

The planet could experience violent eruptions...

..as the gravitational pull of the gas giant

triggers intense volcanism...

..each time it passes by.

But Kepler-36b could also be...

..a planet of ice.

Because if it's tidally locked,

the far side would face permanently away from the star...

..and we could imagine a freezing cold hemisphere

shrouded in eternal darkness.

For now, this is all just informed speculation.

But we are beginning to build a picture of these worlds.

I mean, imagine a world where the sun stays at the same point

in the sky forever,

so one side of the planet is in eternal night

and the other side in eternal day.

And even the twilight strip between day and night,

we think, would suffer from extreme conditions.

So Kepler-36b just goes to show there's so much more

to having a habitable world than just the composition of the planets.

There's the details of its orbits

and also the nature of the other objects in the solar system

that are orbiting around the star with it.

Kepler-36b is just one of thousands of planets

that Kepler has discovered.

We now know beyond doubt that our galaxy is home

to a diverse collection of alien worlds.

Each one of the over 4,000 planets that we've discovered to date

is different from all the others.

They really are an alien and exotic bunch,

and there's certainly no planet that's identical to the planets

that we know of in our Solar System.

And I think that reveals a deep truth about the universe,

because although the laws of nature that form the planets are simple

and the same everywhere and the fundamental ingredients

out of which the planets are made are simple and the same everywhere,

the nature of a planet also depends on the history of its formation

and the environment around its parent star

out of which the planet formed.

And those are all radically different.

So, each planet has a different story to tell.

I suppose, in that sense, planets are like human beings.

And this wholly unexpected but exciting discovery

certainly complicates the search for life.

We needed to narrow the search...

..for planets further but not too far away from their parent stars...

..planets at just the right distance for their surfaces

potentially to be habitable...

..alien worlds with one precious ingredient

that makes Earth a living planet.

Now, you might legitimately ask,

"Can we transfer all the knowledge we have of life here on Earth

"to planets elsewhere in the universe?"

Well, I would answer emphatically, yes, we can,

because the laws of nature are universal.

So, the laws of physics and chemistry that underpin biology here

on this planet will apply to every planet out there in the universe,

whether we've discovered it or not.

The chemistry of life requires a few basic ingredients -

carbon, nitrogen, oxygen, iron.

And it also requires a ready supply of high-quality energy

from heats within the planets or perhaps from starlight.

But life here on Earth also requires one very important, fundamental

extra ingredient, which is liquid water.

Liquid water is a deceptively complicated substance.

It's a very powerful solvent, but it also has structures

which are constantly forming and disappearing within it,

which act as a kind of scaffolding around which biology happens.

Organic molecules are orientated by that scaffolding

so they can react together.

Now, it is certain that every living thing here on Earth

requires liquid water to survive,

and I would say it is a very good assumption that every living thing

anywhere out there in the universe will require it too.

The universe is filled with water.

Great reservoirs have been detected throughout the galaxy

amongst the gas clouds of giant nebulae.

But just because water is plentiful, that doesn't mean that

it necessarily ends up in oceans on planetary surfaces.

Of the eight planets in our Solar System,

only one has liquid water flowing permanently on its surface today...

..an ocean world where, long ago, life began.

Around 4 billion years ago, life on Earth would have begun,

probably in places not dissimilar to this,

where there's geothermal activity, a source of energy in contact

with rich concentrations of reactive chemical elements and minerals,

but also, crucially, that - the magical solvent, liquid water.

Now, many rocky planets out there in the galaxy will probably have this,

but far fewer, we think, will have that -

large bodies of liquid water on the surface.

So that's why there's a kind of a catchphrase

in the astrobiology community, which is,

"If you want to search for life, follow the water."

Whilst life on Earth was evolving...

..124 light-years away...

..amidst a collapsing cloud of gas, dust and ice...

..a small star was born...

..and the cloud-swirling leftovers condensed to form a brand-new world.

In 2015, Kepler found a planet

orbiting comfortably within its star's habitable zone.

More than eight times the mass of the Earth, K2-18b is a giant...

If the planet is rocky, this may have allowed it to hang on

to a thick atmosphere.

K2-18b might have all the makings of a water world.

And a legendary space telescope had Kepler's new discovery

in its sights.

The most powerful space telescope of them all had joined the hunt.

Hubble examined the light from K2-18b's parent star

as the planet passed in front of it...

..and detected what may be a faint signature...

..of water vapour.

124 light-years from Earth...

..we may have at last found the evidence of water

on an alien world.

This was the first observation of water vapour in the atmosphere

of a planet orbiting in the habitable zone around its star.

Now, admittedly, measurements of the amount of water vapour

in the atmosphere is pretty wide.

It's somewhere between 0.01% and 50%.

I mean, this is a planet that's a long way away,

but for comparison, our planet has a few percent water vapour

in its atmosphere.

So, that observation is important for two reasons.

One is, it is not zero.

There is water vapour in the atmosphere.

But secondly, if the measurement is at the lower end,

a few percent of the water vapour in the atmosphere,

then that is consistent with this world being a planet

with oceans on its surface.

The nature of this planet is currently the subject

of intense scientific debate.

The planet may be more like a mini-Neptune...

..a gas planet.

But it is possible to dream of a rocky alien world

with skies full of clouds...

..where water droplets collect...

..and eventually fall...

..feeding vast oceans...

..that cover the surface of a massive planet...

..a water world...

..where the elixir of life...

..is in plentiful supply.

K2-18b is exciting because it's the smallest world

with an atmosphere that we've been able to analyse,

and we've found that its mass and density,

composition of its atmosphere and its orbits

are consistent with it being a world with water.

And it might be a world with oceans on its surface.

We don't know for sure.

But just imagine what that small, faraway world

around a faint red star might be like.

Kepler went on to make many more discoveries...

..until, in October 2018, it finally ran out of fuel.

After nine years, it had found over 2,500 alien worlds...

..showing us just how common

potentially Earth-like planets might be.

We estimate that there may be around 20 billion

potentially Earth-like worlds -

that's rocky planets in the habitable zone around a star

that may support liquid water on the surface - in our galaxy.

That is 20 billion potential homes for life.

Now, we don't know the probability that, given the right conditions,

life will begin on a planet, but we do have evidence from our world.

What we know is that here on Earth, life began pretty much

as soon as it could after the Earth had formed and cooled down

and the oceans formed on its surface.

So that might suggest that whilst there isn't a sense of inevitability

about the origin of life given the right conditions,

it might at least be reasonably probable,

so I think that there is at least a chance that life may have begun

on some, perhaps many, of those 20 billion Earth-like worlds

out there in our galaxy.

But I think there are two questions about life.

One question is about the origin and the existence of microbes.

But often, when we speak about aliens, what we really mean

is not microbes but complex creatures.

We need things that we can speak to, civilisations.

What is the probability there will be other civilisations out there

in the Milky Way?

Well, again, the answer is we don't know.

But there are observations we can make, patterns we can see

in the Milky Way, that might allow us to make an educated guess.

We don't know precisely

how we highly intelligent, complex creatures came to be here.

But we do know for certain that life on Earth didn't begin this way.

We are the product of a story that has been playing out

for over a quarter of the age of the universe...

..from microbes...

..to a global technological civilisation reaching out

for others.

For now, at least, we remain surrounded by silence.

The messages we've sent out into the cosmos remain unanswered,

and the telescopes we use to scan the skies for alien signals

remain quiet.

Now that's not to say, of course,

that there aren't other civilisations out there.

We may have been looking for the wrong thing in the wrong place.

But I think the answer to the question of the great silence

can be found here on Earth, because, here,

it took 4 billion years of stability for a civilisation to emerge.

That is a vast amount of time.

And when we look to the other worlds out there in the Milky Way,

it's those two things - stability and time -

that appear to be very rare commodities indeed.

In 2013, the European Space Agency launched the Gaia Space Telescope.

Its mission? To survey the stars of our galaxy, the Milky Way.

Billions of stars have been mapped...

..each star a potential host for alien worlds.

And patterns are already beginning to emerge.

Not all stars exist alone.

Some have company.

And bizarre as they seem,

Gaia has discovered around a million of these binary

or multiple star systems.

We've known for a long time that binary star systems

and, indeed, multiple star systems exist,

but we didn't know precisely how common they are.

But now we have a huge amount of high-precision data,

including the Gaia data, which tells us that around 50%

of all sun-like stars are in multiple star systems.

And for more massive stars, that number is 80%.

So how does the prevalence of multiple star systems in the galaxy

shift the odds in the hunt for another Earth?

Could Earth-like planets exist in multiple star systems?

And if so, what might their fate be?

In 2020, we may have found a clue,

a planet the size of Mars floating freely through the galaxy,

a so-called "rogue world".

But planets can't form alone in interstellar space,

so where did it come from?

Dawn...

..ushered in not by one star...

..but two.

Perhaps the rogue world grew up in a close binary system...

..subject to the gravitational pull of two stars.

Its orbit may have been unstable...

..as its parent stars fought to control its destiny.

Even in single star systems, the weak gravitational interactions

between the planets can change their orbits.

Now, in a double star system,

the planets are not only subjected to the gravitational pulls

of each other, they're subjected to the stronger gravitational pull

of another star.

So, even if a planet gets into a stable orbit,

it's very likely that it won't stay in that orbit for long.

So, in double star systems, the line between order and chaos

is very thin indeed.

Even subtle changes in a planet's orbit

can lead to dramatic changes in climate.

And that's why the surface conditions on planets

in double star systems may be unlikely to remain stable enough

for long enough for intelligent life to evolve.

And the changes in the orbits of planets

can sometimes be anything but subtle.

A close encounter may have given the rogue world

a final gravitational kick.

Flinging it outwards.

And releasing it from the grip of its parent stars.

Setting it loose...

..on a journey through the galaxy.

Far from the warmth of its stars,

any liquid water the rogue world might once have had...

..would have frozen solid.

Any atmosphere that once protected it...

..would have frozen out on to the surface.

The rogue would have become a world...

..with conditions that no living thing could endure.

An entire planet alone and adrift.

Only to be detected by us millions of years later.

A small Earth-like rogue planet...

..roaming the darkness of space for eternity.

This lonely wandering planet is not a unique world.

Although rogue planets are very difficult to detect,

it's estimated that there may be

over 100 billion of them in our galaxy.

Rogue planets might be the most common

type of planet in the Milky Way.

And although we think most of them

were torn away from their star soon after formation,

this does suggest that star systems are not always stable places

where complex life could evolve over billions of years.

Our hunt for another living planet has only just begun.

Yet we've already learned so much.

We found our first rocky worlds.

Some in the habitable zone around their stars.

Some, potentially, with liquid water on the surface.

Candidate worlds for future missions to search for evidence of life.

But we've also found hordes of bizarre, tortured worlds...

..orbiting around violent stars.

And a multitude of rogue planets...

..where complex life as we understand it seems impossible.

Perhaps it's these worlds that hint at the reason why...

..for now, one planet stands apart.

Alone.

Our planet seems to have largely escaped the violence,

the chaos and the constant change

that seems to characterise a galaxy like the Milky Way.

Yes, there's been the odd mass extinction,

but there's been an unbroken chain of life here on Earth

stretching back four billion years.

And if that's what you need to go from the origin of life

to a civilisation, then although there may be billions of worlds

out there where life began, there may be very few civilisations.

But that's just an opinion.

It's an educated guess.

And given the profound nature of the question,

no matter how educated the guess, I think it would be ridiculous

for us to stop looking, both inside our galaxy and beyond.

For we may have just received the first glimpse

of a world beyond the Milky Way...

..around 30 million light years away,

nestled in the spiral arms of the Whirlpool Galaxy.

A world the size of Saturn.

A find that marks an expansion of our horizons.

The beginning of the hunt for extragalactic planets.

The potential discovery of a planet orbiting around a star

in another galaxy is something that I never thought I'd see.

And it opens up the intriguing possibility that we might be able

to explore not only the question, "Are we alone in our galaxy?"

but "Are we alone in the universe?"

The answer to that question may lie far in the future.

We might never answer that question,

but I said the question "Are we alone?" is profound

because answering it would teach us much more

about what it means to be human.

Well, I think we become a little bit more human with every world

that we explore because that ability to lay the foundations,

to explore questions to which we may never receive answers

in our lifetime, questions for our children

or our grandchildren to answer

is a fundamental part of what it means to be human.

It's a fundamental part of what makes us so special

here on this little world, looking up at the stars,

whether we're alone or not.

Five, four,

three, two...

Engine start. One, zero,

and liftoff of the Delta II rocket with Kepler

on a search for planets in some way like our own.

We had worked to get thousands of people to work together

and it's all coming together.

And we have separation.

It was so emotional to see the project they had worked on

for so many years or decades finally go to space

and all that hope and promise all bundled up in the machinery.

Kepler was an immediate success,

discovering over 2,000 new planets

in its first four years of operation.

But in the summer of 2012,

the team faced a challenge that threatened the entire mission.

One of the things that the Kepler mission needs to operate

are reaction wheels that spin and hold it on target.

So it always points at the same stars and doesn't jiggle.

Well, we had four wheels that did that.

And we knew that we only had a couple of spare gyroscopes,

and we knew that spacecraft tend to have gyros fail.

And after a while, it failed.

Three months later, the second one failed.

And since we needed three,

we could no longer look at the Kepler field of view.

I had hoped that they'll figure out a way to work with two gyros,

and indeed they did.

So the very clever people, the engineers and scientists,

said, "What we can use is we'll use the sunshine for the third wheel.

"We'll make this thing reflect sunlight off it,

"we use the other two wheels and now we can point in the sky."

The faint pressure of sunlight helped stabilise the telescope.

That was kind of good news, actually, because it meant Kepler

was going to have to go off the Kepler field now

and we could get all kinds of other stars and observe them.

And so, it actually was a boon for stellar astronomy.

After another four years of discoveries,

in total it had found over 2,600 planets,

making it, by far, our most successful planet hunter to date.

It was sad when they said to command to shut everything down.

You know, it's asleep now,

it's in orbit around the Sun and it will continue that orbit,

but since it launched from Earth, it will come back to Earth.

It'll come and visit us again in about 40 years.

And my hope is people will say,

"This is a historic telescope. It told us about all these planets."

And they will go up and pick up this telescope and bring it back to Earth

and put it in the Air and Space Museum for us all to admire.

Next time...

..a powerful new space mission uncovers the history of our galaxy,

the Milky Way.

How it arose from the universe's mysterious dark age...

..and overcame a series of enormous collisions

with rival galaxies

that paved the way for our own arrival

inside one of its magnificent spiral arms.

Journey through the universe with the Open University

and learn more about stars, planets and galaxies with this free poster.

Order your poster by calling 0300 303 5746.

Or go to bbc.co.uk/theuniverse

and follow the links to the Open University.

I can see everything quite clearly.

It has a stark beauty all its own.

# See me when I float like a dove

# ..The skies are lined with trees... #

Magnificent desolation.

Beautiful. Beautiful.

Ain't that something?

# ..Come and take me away... #

If I were to ask you, where do you come from...

..what would you say?

What story would you tell?

You might say, well, I come from my hometown.

Or my city or my country.

If you've got a particularly wide perspective, you might say,

"I come from planet Earth."

But what is the largest structure that we could

legitimately call home?

Well, I would argue it's that.

That faint arc of light that stretches

across the sky from horizon to horizon.

It's an outer spiral arm of our galaxy, the Milky Way.

Our home island of 400 billion stars.

The Milky Way takes its name from the dense band of stars

that sweeps across the sky on the clearest of nights.

From our vantage point here on Earth,

we see the galaxy from within.

But if we could travel outside the galaxy...

..we would see the entire structure.

The Milky Way revealed as an island of light surrounded by darkness.

Hundreds of billions of stars in a single disc...

..that's existed since the universe was young.

Only now are we able to explore its history.

LOW RUMBLING

How it was born.

How, through a series of remarkable events,

it grew to become the galaxy we inhabit today.

And how, eventually, it will end.

We've discovered our own paths in this story, too, living as we do

inside the Milky Way,

just over halfway along one of its magnificent arms...

..around a small but familiar star.

The Milky Way is an island, in a sense.

Every star you can see

in the night sky is a part of our galaxy.

Our nearest neighbour in large galaxies

is over two million light years away.

So it certainly feels as if we are isolated and alone,

adrift in an ocean of dark.

And that is true to a point.

There is no conceivable technology that will ever allow us

to leave our island physically,

but science allows us to leave the Milky Way in our imaginations

to view our galaxy from impossible perspectives in both space and time

and to tell its story.

WOMAN SPEAKS FRENCH

SHE COUNTS DOWN IN FRENCH

Decollage!

One mission more than any other has deepened our understanding

of the galaxy.

A spacecraft bearing the name of an ancient Greek goddess.

Everything functioning beautifully.

Gaia.

Coming up on separation of the boosters.

Ancestral mother of all life on Earth.

The four boosters, the four points of light, are falling away.

Gaia's mission?

To map the locations of billions of stars in the Milky Way...

..nearly all of them for the first time.

Gaia spins on its axis...

..its sensors scanning the galaxy in all directions.

Every star is mapped an average of 70 times...

..allowing Gaia to calculate the speed and direction of each one,

pinpointing their locations

with accuracies up to one-thousandth of 1%.

Over 1.5 million stars every hour.

Almost two billion in total so far.

To create a map like nothing ever seen before.

The Gaia data is by far the most detailed star map ever produced,

a revolution in our understanding of the Milky Way.

This is the data, and it looks like

an artist's impression of a galaxy, something from science fiction,

but this is a high-precision 3D map of our home,

of our island of stars,

and we can even fly through it,

such is the precision of the mapping of the position.

All these points of light are stars,

some of them as far as 30,000 light years out from the solar system.

The map allows us to journey through the galaxy

at impossible speeds...

..bringing distant stars within reach.

But this is also a journey through time.

The extraordinary thing about this map is that it's alive,

in a sense. I mean, Gaia didn't just measure the positions

of these stars. It measured their velocities.

That means we can tell where those stars are going,

what the galaxy is going to be like in the future,

but also we can tell where they came from.

So what the galaxy was like in the past.

By reversing the direction of every star...

..we can rewind their histories...

..travelling backwards in time through billions of years.

Gaia has initiated a new science,

a science of galactic archaeology,

where we can ask questions about the origins

of our galaxy itself.

LOW RUMBLING

The first galaxies emerged just a few hundred million years

after the Big Bang.

The universe was crisscrossed by a vast structure

known as the cosmic web.

Great filaments of dark matter,

along which gravity attracted ever denser concentrations of gas...

..separated by immense tracts of empty space.

The first stars were born where the filaments crossed,

where the gas was dense enough to collapse under its own gravity...

..and for the stars to ignite.

New stars formed in their billions...

..bound together by their mutual gravitational pull.

These were the first galaxies.

Amongst them, the Milky Way

in its embryonic form,

far smaller and more irregular in structure

than the mature spiral galaxy we inhabit today.

The exact details of the Milky Way's birth remain the subject

of research, but thanks to modern-day observations, the story

of how our galaxy grew from those early beginnings

is coming into much sharper relief.

The Gaia data allows us to see how the Milky Way evolved

throughout its history,

and one of the clues that it's had an interesting history

can be seen in this animation.

You can see that most of the stars orbit in very regular orbits

around the centre of the Milky Way -

that's exactly what you'd expect -

but you can see here that some of the stars

have very different orbits indeed.

They seem to be flying all over the place.

And that tells us that something dramatic happened at some point

as our galaxy made its way through the universe.

Across the universe,

hundreds of billions of galaxies were forming.

Some, just a few dozen, were born close enough to the Milky Way...

..that their mutual gravitational pull drew them together...

..forming what we now know as the local group of galaxies,

our home archipelago.

DRAMATIC MUSIC PLAYS

Six billion years before the Earth formed,

some of the Milky Way stars already had their own planets.

Early worlds that were about to witness

the transformation of the galaxy.

The wonderful thing about astronomy is that you can look

up into the sky, and even if you can't see worlds,

you can imagine them and you can imagine their stories.

Over there...

..close to the bright star Vega is Kepler-444,

the faint ancient star, and planets orbiting around it,

that's witnessed pretty much the entire history

of the Milky Way galaxy.

And then maybe swing around in the sky...

..just close to the planet constellation

that everybody can recognise

and follow it down.

There's a really faint star there.

You can't see it with the naked eye.

It's so nondescript it doesn't even have a name. It's got a number.

It's called HD 73394.

But that star is an alien star.

It was born in another galaxy,

and it entered the Milky Way

in a galactic collision with a smaller galaxy.

And Kepler-444 over there witnessed it all

and witnessed the Milky Way being thrown into chaos.

LOW RUMBLING

Kepler-444 was orbited by five planets.

And something new had appeared in their skies.

A smaller galaxy was approaching the Milky Way...

..with stars that burn bright blue.

Gaia Enceladus.

A member of the local group,

roughly a quarter of the size of our own galaxy.

Over hundreds of millions of years, the galaxies collided...

DRAMATIC MUSIC PLAYS

..the stars of Gaia Enceladus penetrating deep

into the Milky Way's heart.

But our galaxy held its ground...

..capturing billions of incoming stars.

An entire galaxy swallowed whole.

These alien stars remain in our galaxy to this day.

The Gaia data tell us that collisions are the driving force

of galactic evolution.

Some galaxies cease to exist as independent islands of stars...

..while others grow and prosper.

The survival of the fittest writ large.

When galaxies collide -

that phrase puts images of Hollywood disaster movies into the mind -

stars getting ripped apart, but that's not what happens at all.

I mean, if you imagine that our sun...

..let's say the size of a small pebble or a grain of sand,

the nearest neighbouring star in this region of the galaxy

will be somewhere over by those hills.

The distances between stars is immense.

The stars don't collide,

so when galaxies interact, the stars get scattered.

The shape of the galaxy changes, but nothing gets destroyed.

And in fact, sometimes galactic collisions

can be engines of creation.

Gaia Enceladus, the alien galaxy,

had brought with it fresh supplies of interstellar gas.

The raw material of star formation.

For a time, this gas heightened the rate at which the Milky Way

could produce new stars...

..helping it to grow.

But long before our star was born,

the Gaia Enceladus collision era drew to a close.

What triggered the formation of the sun

has long remained a puzzle.

But the Gaia telescope has discovered

new clues to its origin...

..in the events that followed billions of years later...

..as our island of stars continued to evolve.

UPLIFTING MUSIC PLAYS

On the distant shores of the Milky Way,

Gaia has investigated a structure of epic proportions.

A stream of stars winding their way around the galaxy.

This stream of stars is enormous.

It's almost unimaginable in scale.

Look up into the night sky, those stars that you can see

are at most a few thousand light years away.

Think about that - the light began its journey to your eye

from the most distant stars when the pharaohs ruled Egypt.

And then if you look out to the Milky Way,

to the shores of our galaxy,

you see light from a few tens of thousands of light years away.

I mean, that light began its journey when there were Neanderthals

here in Europe.

But this stream of stars wraps around the galaxy.

It's hundreds of thousands of light years in extent.

A structure that large demands an explanation.

The stream is wreckage, it's footprints, if you like,

of a very violent event.

Gaia has confirmed the origins of this immense structure...

..through the telescope's unique ability to help us

travel through time...

..backwards.

The data tell a story...

..of a new age of star birth.

Of the transformation of the Milky Way

triggered by another galactic collision.

It was another galaxy from our local group.

Sagittarius Dwarf.

Perhaps 20 times smaller than the Milky Way,

it was torn apart in the impact.

Sagittarius Dwarf brought fresh supplies of the vital ingredient

for star birth.

HISSING

That is the sound for the most common element in the universe.

This radio telescope is pointing towards the Milky Way,

which has just risen above the horizon over there

behind the clouds.

And what you're listening to this hydrogen gas.

HISSING CONTINUES

The radio telescope is detecting the faint signal of hydrogen

from across the galaxy.

Hydrogen is found throughout the Milky Way,

sometimes in the form of towering clouds, light years high.

These regions are star factories,

where the dense clouds of hydrogen gas collapse under gravity...

..to forge new stars.

Hydrogen atoms radiate radio waves

at a very particular wavelength, 21 centimetres.

And as I speak, that radiation is being captured

by that radio telescope.

Imagine - there are atoms over there, and by over there,

I mean, what, thousands, tens of thousands of light years away.

At some point, way, way back in the past,

out came the radiation,

and we can listen to it.

So we're listening to the lifeblood of our galaxy.

As Sagittarius Dwarf passed through the Milky Way,

it brought fresh gas AND fresh energy.

The impact sent ripples across the Milky Way...

..triggering another spectacular era of star formation.

And in the outer regions of the galaxy...

..our own star was born.

The sun was soon joined by the Earth...

..and together,

they set out on their journey through the galaxy.

We were born in the Milky Way...

..but we may have been conceived in a collision.

Now, we can't say for certain that the collision

with Sagittarius Dwarf caused the formation of our sun.

The date is not precise enough

and our understanding is not deep enough for that.

But what we can say is that the birth of the sun coincided

with enhanced rates of star formation in the Milky Way

caused by that collision.

But that's not quite the end of the story,

because in a very real sense, the collision is still under way.

The remains of Sagittarius Dwarf

are still orbiting on the fringes of the Milky Way.

Over the last five billion years,

the galaxy has crossed our path two more times...

..each interaction triggering a new generation of star birth.

A fresh sprinkling of light inside our galaxy's spiral arms.

The finishing touches on a masterpiece of galactic creation.

The poet John Donne famously wrote,

"No man is an island entire of itself,

"every man is a piece of the continent, a part of the main,"

by which he meant that no human being can isolate themselves

from the rest of humanity because origins and our fates

are so deeply intertwined,

and therefore we must care deeply for each other.

And the same is true for galaxies.

No galaxy is an island entire of itself,

and the history of the Milky Way stretches back

13 billion years or more.

That's pretty much for the entire history of the universe,

and its story is a story of collisions and interactions

between galaxies of rivers and flows and streams of stars

stirring up the void and triggering the formation of worlds like ours.

You, me, everyone can trace our origins back

to a collision between galaxies.

You may be small, but you are a consequence of grand events.

And those grand events haven't stopped.

It just feels like it because we don't perceive events

that play out over billions of years involving billions of stars.

But the unique thing about this time in history is that we can speak

with some confidence, not only about our galaxy's past, but also

about our galaxy's future.

And just as inexorably as those great islands of stars

drift through the universe, change will come again.

We move into the future with a new understanding of our place

in the galaxy.

We are inhabitants of a small planet

orbiting around an ordinary star,

where something extraordinary has happened.

But although the galaxy made us, it wasn't made FOR us.

We are accidental by-products of its history.

And we will be passive witnesses to its ongoing evolution.

The Milky Way is the great survivor,

and the echoes of its turbulent history are literally

written across the sky. Over there, in the southwest,

the remnants of Sagittarius Dwarf, the debris from that collision

is still wandering around somewhere on the fringes of the Milky Way.

And in that direction, as Sirius rises in the east

in the constellation of Canis Major,

there are the remains of another dwarf galaxy

that we think collided with us long ago.

So the Milky Way pretty much devours anything that comes into this region

of space because it's the largest galaxy in the neighbourhood...

..except for one.

The local group is home to another galaxy that rivals our own in size.

The galaxy that's been hiding in plain sight.

Right up there,

just between the constellations of Cassiopeia

and the square of Pegasus,

is a faint misty patch of light in the sky,

about twice the diameter of a full moon,

so you can certainly see it with binoculars.

And even in the city, I can take a photograph of it

with the camera like this.

And there it is!

That object is the Andromeda Galaxy.

And you see that it's a spiral shape.

You can see it even in this photograph.

In many ways, Andromeda is our twin.

And it's a twin that we've been able to explore in incredible detail.

Three, two, one.

And liftoff of space shuttle Atlantis

on a final visit to enhance the vision of Hubble...

..into the deepest grandeur of our universe.

Standing by for SRB separation.

The Hubble Space Telescope

is in its fourth decade of operation.

Its ongoing mission has given us some of the most detailed images

of the universe ever seen.

Over the years, Hubble has frequently

turned its attention to Andromeda...

..2.5 million light years from Earth.

It's mapped a spiral structure similar to that of the Milky Way...

..with such fine precision that we've been able to calculate

not only the motion of Andromeda stars,

but also the motion of the galaxy itself.

And we now know that the entire galaxy is heading towards us.

That's over 400,000 kilometres per hour.

Now, you may think, well, what's one more collision?

I mean, the Milky Way has survived all these collisions

for pretty much the entire history of the universe.

Well, this one will be different because Andromeda is bigger than us.

The Milky Way, as we know it today, will not be immortal.

And the Earth will witness its demise.

Two galaxies in a single sky,

gradually, but inexorably, merging into one.

In the impact, there will be a last, colossal burst of star formation.

But this will be very different to previous collisions.

This time,

our galaxy will meet its match.

The great galaxies will distort each of the spiral arms...

..stars will be scattered...

..until no traces of the original structures remain.

DRAMATIC MUSIC PLAYS

The Milky Way's fate is sealed.

Andromeda will be the first of a series of mergers

as the remaining galaxies in our local group converge,

drawn together by gravity.

But Hubble has allowed us to see even further into the future.

It looks out far beyond the local group

towards the edge of the observable universe,

and seeing that every distant galaxy is receding from us.

In a final twist, these retreating galaxies tell us something profound

about the nature of the universe itself.

We live in an expanding universe.

In fact, we live in a universe that's accelerating

in its expansion, so all the galaxies are rushing away

from each other, and in the far future, they'll be rushing away

from each other so fast that even if we sent a beam of light

out to the galaxies, it would never catch them.

Billions of years from now, the remnants of the Milky Way

will form part of a single, gigantic collection of stars...

..the merged remains of the local group...

..alone, as every other galaxy recedes into the distance.

Eventually, all the galaxies will fade from view,

and our galaxy

will stand at last

in perfect isolation.

An island...

..unto itself.

I think we live at a fortunate time in the history of the universe

because we can look into the sky and see the galaxies.

The astronomers of the far future might imagine that they live

in a universe populated by countless billions of islands

of billions of stars, but they won't be able to prove it.

They won't be able to see the true scale and majesty of the universe.

We've been trying to understand the band of stars that stretches

across the night sky since the time of the Ancient Greeks.

This story of our galaxy, the Milky Way, how it started,

how it was formed

and how it transformed is really the story of us.

Inside the Milky Way,

you always have a slightly skewed perspective of the way

the Milky Way looks.

So we're in it.

And so what we would like to do is go above it and look down

and see what it's like.

Now, you can't do that unless you could travel at millions of times

the speed of light, and we can't,

so the only way we can do it is by working out accurately

where all the stars are,

how far away they are from us in particular.

Gaia is a European Space Agency spacecraft, which is, in principle,

a very simple little thing.

It's two telescopes collecting the light, putting it down

onto one giant camera. The biggest camera ever put in space, actually.

It can observe the positions of stars so accurately

that you could see the edge of a euro coin on the moon from Earth.

And that's just mind-boggling.

WOMAN COUNTS DOWN IN FRENCH

Decollage!

It was a beautiful launch, really spectacular.

Then they got into this critical state where they had to open up

the sun shields. It was critical that this opened up

and protect the payload from the sun,

and that was the do-or-die moment.

There's the good news.

APPLAUSE CONTINUES

Gaia works by measuring parallax.

This is exactly the same way your eyes and brain work,

so that you can tell how far away something is

because of the slight difference and angle from this eye to that eye.

And so what we do with Gaia is have a picture in the summer

and a picture in the winter,

and in that stage, Gaia has gone halfway round the sun,

and so its two eyes are twice the radius of the Earth's orbit apart.

And that's how we do parallax.

All this is a big version of your head.

The last data released from Gaia was in December 2020,

and what's been really exciting is that we've been able to get

the distances and the motions of the star

to a much better level of accuracy.

Most of the stars in the disc of the Milky Way

all move in the same direction,

rotating clockwise around the centre of the galaxy,

and one of the most exciting things that came out of

the first data release was that a large sample of stars were found

that seemed to be rotating in the opposite direction

to the majority of stars in the Milky Way disc,

and that's really surprising.

They probably came from a different galaxy altogether,

so there are almost these alien stars that have been brought in.

Alien stars from galaxies that long ago shared our own corner

of the universe.

The important thing to know about our galactic neighbours

is that nothing's actually sitting still.

We're all moving towards or away from each other,

and we're sort of playing a dance out there.

And driving the dance of the galaxies

is the universe's most elusive form of matter.

Dark matter is something that has gravity but produces no light.

It surrounds us.

In fact, it dominates the mass in our own galaxy,

and yet we don't know what it is.

We can't touch it. We can't feel it.

We were able to start measuring very accurately the way stars move

from radial velocities, that's just towards and away from us,

and this allowed us to measure accurately for the first time

how the dark matter was distributed near us.

The team have pieced together how dark matter

orchestrated a series of galactic collisions...

..that spanned billions of years.

Dark matter is really important in galaxy collisions

because it's so abundant,

so it's really driving the gravitational interaction

between the galaxies.

It is dark matter that determines how violent the collision is,

how rapidly and with what intensity

galaxies come together when they collide.

In many ways, it determines how galaxies end up after a collision.

So the thing that Gaia showed us is not that it's plausible

that this happened, it showed it DID happen.

It happened in just this way.

So it's not speculation any more. It's quantitative science.

The galaxy is a dynamic thing. It's a living organism, if you want.

It is breathing, it is changing, it is transforming.

It's all coming together in the end to tell us about how we got here

and what our place in the universe really is.

Next time - we explore our galaxy's supermassive black hole.

A monster that can destroy worlds...

..stop time

and is forcing us to reassess our understanding of reality itself.

Journey through the universe with the Open University and learn

more about stars, planets and galaxies with this free poster.

Order your poster by calling 0300 303 5746,

or go to bbc.co.uk/theuniverse

and follow the links to the Open University.

NEIL ARMSTRONG: I can see everything quite clearly.

It has a stark beauty all its own.

EXPLOSION

MUSIC: Neptune by Foals

BUZZ ALDRIN: Magnificent desolation.

Beautiful! Beautiful! Isn't that something?

The Milky Way seems a tranquil place.

Hundreds of billions of stars

serenely spinning through the cosmos.

But journey inwards through the gas and dust

that shrouds the galactic core...

..and you see a curious sight.

Stars orbiting seemingly empty space.

Something dark and ancient lives here.

A hole in the fabric of the universe.

Every one of those points of light in the night sky

is a strange and fascinating place.

Magnificent suns with countless planets orbiting around them.

Alien worlds beyond imagination.

But the strangest and most fascinating places out there by far

are dark and unseen.

An invisible monster is lurking in the centre of the Milky Way.

A monster that drains the colour from the universe.

With the power to destroy worlds.

And stop time.

We've named the monster Sagittarius A*

and we believe it to be a black hole.

Sagittarius A* has played a major role in the evolution

of our galaxy and may even have influenced

the formation of stars and planets like ours.

But there is so much more, because black holes like Sagittarius A*

present the most profound intellectual challenge.

They are part of nature just like you and me,

so we should be able to understand them,

but they are holes in the fabric of the universe.

They are gravitational prisms from which even light itself

can't escape.

And in trying to understand them, physicists have been led

to completely reassess our most basic understanding of reality.

But there are answers hiding in the void

for those brave enough to seek them.

EXPLOSION

STEPHEN HAWKING: It is said that fact is sometimes

stranger than fiction, and nowhere is that more true

than in the case of black holes.

Black holes are stranger than anything dreamed up

by science fiction writer,

but they are firmly matters of science fact.

EILEEN COLLINS: And we copy. Go for deploy.

You look out and this thing is so big,

you certainly know that it's moving over the head of the shuttle.

In the summer of 1999, Nasa's flagship mission

for X-ray astronomy was released from the shuttle cargo bay.

There is nothing as beautiful as Chandra sailing off

on its way to work.

High above the Earth, Chandra scanned the sky...

..hunting for some of the hottest regions in the universe.

Exploding stars and clusters of galaxies.

But on September 14th, 2013,

after 14 years, Chandra chanced on something else entirely.

The telescope gazed into the constellation of Sagittarius,

hoping to observe a large cloud of hot gas.

Instead, it recorded a flash of X-rays just a few pixels across...

..coming from the apparently empty space in the galactic core.

Something had got very hot for a very short period of time.

It's thought that the flash seen by Chandra

may have been an asteroid tens of kilometres across.

RUMBLING

Ripped apart and burning up in a fireball

300 times brighter than the Sun.

The culprit?

Sagittarius A*.

The asteroid's destruction was our galaxy's black hole

signalling its presence to the world.

20 years ago, we didn't know for sure that there is a black hole

at the centre of our galaxy, but by measuring bursts of radiation

and observing in detail the orbits of stars

close to the galactic centre,

we now know that Sagittarius A* definitely exists

and we've been able to measure its mass.

It is around four million times the mass of our sun,

which makes it a supermassive black hole,

one of the strangest and most powerful objects in the universe.

And we've begun to suspect that Sagittarius A*

isn't just some strange thing that sits tens of thousands

of light years from Earth at the centre of the galaxy.

It has played a crucial role in the evolution of the Milky Way

and the whole story began with the death of one massive star.

Soon after the dawn of time...

..the cosmos was home to colossal stars...

..hundreds of times more massive than the Sun.

Stars that burned blue with intense heat.

But the brightest stars are the shortest lived.

One lived a particularly fast and furious life...

..burning through its nuclear fuel in just a few million years.

And with nothing left in the tank,

gravity took over.

The star collapsed...

..ever smaller...

..ever denser...

..until it seemingly disappeared.

The remnants of the star,

now smaller than an atom,

lost from the universe.

All that's left is a ghost.

A black hole.

The genesis of Sagittarius A* wasn't some bizarre one-off event.

It's possible that almost all early stars

became black holes when they died.

Black holes are simply what happens when gravity goes unchecked,

compacting matter so densely

it tears a hole in the universe.

In the vicinity of a black hole, space and time behave

in very counterintuitive ways.

And in fact, this river provides a beautiful

and surprisingly accurate analogy.

You see, close to a black hole, you can think of space itself

as flowing towards the black hole.

Now, here, the flow is not too fast,

and so you could imagine I could jump into that river,

I can swim faster than the river of space,

and so I can escape out into the galaxy.

But as you get closer to the black hole,

the river of space flows faster and faster and faster.

A collapsed star is so small and yet so massive

that close to it, the gravitational forces become overwhelming.

There is no limit to the speed at which the river of space can flow.

There's a place where the river becomes a waterfall,

where no matter how fast I swim, I could never escape upstream,

and that's what happens in the vicinity of a black hole.

The river of space flows at and then faster than the speed of light.

Light itself can't move fast enough to escape.

And that's what Sagittarius A* is.

It's a waterfall in the fabric of the universe.

From the moment the black hole formed,

the seed of Sagittarius A* had a heart of pure darkness.

The interior forever hidden from view.

Shielded from the rest of the universe by a boundary in space.

The event horizon.

The ultimate point of no return.

As we approach the event horizon,

we get our first glimpse of the true weirdness of black holes.

Einstein taught us that space and time are not what they seem.

They are merged together into a kind of a fabric -

- the fabric of the universe. It's called space time.

And Einstein also taught us that the presence of massive objects -

stars and planets and galaxies - curved and distorts

the fabric of the universe.

And that's what we feel as the force of gravity.

But that distortion is not only in space, it's also in time.

As you go closer and closer to a massive object,

the rate that time passes slows down.

So if I look towards a black hole,

I see time passing slower and slower and slower

until, on the event horizon,

time stops.

Sagittarius A* was born a waterfall

in the fabric of the universe...

..where space flows faster than light

and time grinds to a halt.

But our black hole was still just a baby...

..dwarfed by the stars around it.

It was nothing like the monster it would become.

Sagittarius A* today

is four million times the mass of the Sun.

There has never been a star that massive.

So it must have formed by the collapse of something much smaller

and then it must have grown over the lifetime of the Milky Way

by eating stuff.

Unfortunately, there has been a lot of stuff around for it to eat.

The young black hole's inexorable gravitational pull

meant there was no escape for anything that strayed too close.

Sagittarius A* began to grow...

..pulling on nearby stars...

..before ripping them to shreds and feasting on the hot plasma.

The black hole gaining more mass...

..and more gravitational power.

But we don't think there were enough stars nearby

for the black hole to grow supermassive

on a diet of stars alone.

Instead, it developed a taste for more massive prey.

When another black hole passed close to Sagittarius A*,

they became locked in a gravitational embrace...

..spiralling towards each other, approaching half the speed of light.

Before colliding.

Sagittarius A* cannibalised its cousin...

..creating ripples in the fabric of the universe itself.

More meals were to follow.

Black holes, stars, gas clouds -

whatever ventured too deep into its lair.

And as our black hole's power and influence grew...

..its surroundings were changing, too.

Around the galactic core,

hundreds of billions of stars were in orbit...

..slowly spinning around their common centre of mass...

..evolving into the familiar spiralling disc...

..the majestic Milky Way...

..with Sagittarius A* at its core.

Sagittarius A* became what we now call a supermassive black hole,

many tens or even hundreds of thousands of times more massive

than any star in the universe.

And Sagittarius A* is not unique.

We now think that virtually every large galaxy

has a supermassive black hole at its heart.

Chandra has looked beyond the Milky Way

and observed countless supermassive black holes lurking at the hearts

of the myriad galaxies that litter the cosmos.

These monsters aren't obscure quirks of nature.

They are fundamental features of it.

And far from being bit players,

we're starting to realise that black holes

have the power and reach to sculpt the galaxies around them.

The centre of our young galaxy was rich in gas and dust.

More offerings to feast on.

This was a gluttons period

that marks a new era for the Milky Way's supermassive black hole.

When the invisible monster became sculptor of the galaxy.

Creation and destruction often go hand-in-hand in the universe

and black holes are no exception.

Sagittarius A* is certainly not only an agent of destruction

because the material that falls inwards towards the black hole

doesn't all vanish across the event horizon.

A lot of it goes into orbit around the black hole.

And that region is tremendously violent.

There are magnetic fields that swirl around

and become twisted and distorted, and they can throw material out

along the magnetic poles of the black hole,

making jets that sweep through the galaxy.

It's only recently that we've grasped the true scale

of Sagittarius A*'s eruptions.

Engine start.

One, zero!

Lift off.

The Delta rocket carrying a gamma-ray telescope

searching for unseen physics in the stars of the galaxies.

Just over a decade ago, a completely unexpected discovery was made,

likened to finding a brand-new continent here on Earth.

The Fermi Space Telescope was built to detect gamma-rays,

the most energetic radiation in the universe.

As Fermi orbited the Earth, it constructed a map of the sky...

..and saw, emerging from the plane of the Milky Way...

..two colossal bubbles of material,

each 25,000 light years across.

These bubbles are superheated gas.

If our eyes were sensitive to the wavelengths of light

emitted by those bubbles, they would span half the sky

as seen from here on Earth.

And they point back to the centre of the galaxy.

It looks like their origin is Sagittarius A*.

Think about that.

Sagittarius A* is big but not big on a galactic scale.

It would fit comfortably inside the orbit of Mercury

in our solar system.

Though our black hole is only a fraction of the size

of the galaxy around it...

..it had become sculptor of the Milky Way.

Every few million years,

the dense ring of material circling our black hole...

..was accelerated by twisting magnetic fields...

..into fiery jets of superheated matter.

Jets so powerful they stripped the atmospheres

from any planets in their path.

And radiation rendered every Earth-like world

within a thousand light years uninhabitable.

But such was the scale of Sagittarius A*'s outbursts

that far, far out in the galaxy...

..destruction...

..turned to creation.

If you're looking for reasons why life not only began here on Earth

but was able to prosper for the almost four billion years it took

for it to evolve into the complex living world that we see today,

then it might seem a bit of a stretch

to point to a supermassive black hole at the centre of our galaxy

and say that's one of the reasons why.

But we're now beginning to suspect that those great outpourings

of energy from Sagittarius A* played a crucial role

in making this region of the galaxy one in which life can flourish...

..because the hot gas ejected by Sagittarius A*

had a calming effect on the galaxy.

Now, you might think that a hot gas cloud would produce more stars,

but, in fact, the opposite is true,

because hot means that everything is moving around very fast

and that makes it more difficult for gravity to grab hold of everything

and collapse it to form stars.

So Sagittarius A* reduced the number of stars

that formed in this region of the galaxy.

And that's a good thing.

Imagine if there was some giant star that had formed close by

the exploded in a supernova explosion.

That would not be a good thing if you're an amoeba

and you have designs one day on evolving into Einstein.

So, Sagittarius A* turned what is potentially a violent region

of our galaxy into a peaceful one.

The warm gases pushed out by Sagittarius A*

slowed the rate of star formation.

And, around one small yellow star in a quiet region

at the unfashionable end of the outer spiral arms of the galaxy...

..four billion years of stability

made all the difference.

Now, of course, there are many things that are necessary

for life to exist on a planet.

The list is unimaginably vast, but I think it is interesting

that on that list there is the presence of this strange object,

a black hole, Sagittarius A*,

tens of thousands of light years away.

The centre of our galaxy.

Having cleared out much of the gas, dust and stars

that once lay close by...

..there was little left to feast on.

Our black hole fell silent.

The enormous bubbles spotted by Fermi...

..echoes of a glorious past.

Today, Sagittarius A* is a sleeping giant...

..a brooding beast...

..operating on a slow simmer.

Sagittarius A*'s journey from violent destroyer

to sculptor of the galaxy to the sleeping giant that we see today

has been pieced together over the last 20 years by observational data

from telescopes such as Chandra and Fermi.

But there's a very big difference indeed

between knowing how a black hole interacts with its environment,

how it sculpts a galaxy,

and what it actually is at a deep level.

What is it really like inside?

STEPHEN HAWKING: Black holes challenge the most basic principle

about the predictability of the universe

and the certainty of history.

Nothing can get out of a black hole,

or so it was thought.

It's by looking into the future that we're beginning to explore

the deep mystery of black holes.

Dozens of stars orbit around Sagittarius A*.

Some passing just a few billion miles from the event horizon.

A hair's breadth on galactic scales.

These flybys could have fatal consequences.

Some of these stars will likely have planets in orbit.

Planets that may stray too close to the beast.

A moth to a flame.

Pulled from its parent star towards the abyss.

If the planet survives its journey inwards...

..and we could stand on its surface

and look out into the universe beyond...

..we would see space and time becoming increasingly distorted.

But eventually, tidal gravitational forces become too strong.

Inexorably, the singularity awaits.

The end of time,

where all paths terminate.

Over trillions of years, all the stars around Sagittarius A*

will gradually fade and die.

On more and more alien worlds, the dawn will fail to come.

But our supermassive monster will go on,

its secrets sealed away inside.

Seemingly forever.

We predict that one day black holes will be all that remains

in the universe. The final Dark Age.

BIRD CAWS

If nothing can ever escape from black holes, if Sagittarius A*

really is an eternal prison, then this is the end

of the story of the universe.

Darkness littered with holes in space time.

But we don't think this is the end of the story.

We now believe that even black holes die.

And their deaths come at the hands of what might seem

an inconsequential detail discovered almost five decades ago.

In 1975, Stephen Hawking published a remarkable paper

in which he showed that black holes are not completely black.

They glow faintly. They have a temperature.

And here's his beautiful equation for the temperature of a black hole.

And you can see that there's something deep going on

because this has got all the physics in it. With this thing here,

h-bar, it's Planck's constant and that's to do with quantum mechanics,

a subatomic world. C is the speed of light.

G is the strength of gravity.

This kB here is Boltzmann's constant,

that's to do with temperature and thermodynamics.

And this M here is the mass of the black hole.

It's even got circles because it's got a Pi in it.

Hawking's conclusion proved to be irrefutable,

and the implications are huge.

If something has a temperature, then it radiates.

That's why if you put your hand near something that's hot,

you can feel it. And so over timescales that are billions

and billions and billions and billions of times longer

than the current age of the universe,

Sagittarius A* will eventually evaporate away.

Very gradually, the Hawking radiation

will erode Sagittarius A*.

Smaller and smaller.

Until many trillions and trillions of years into the future...

..in a final burst of light...

..our black hole will die.

And then there will be darkness.

For all eternity.

Now, you may say, quite legitimately,

"Well, why do we care?

"Why does it matter if black holes evaporate away

"some time in the far, far future of the universe?

"There'll be nobody around to see it."

But the discovery that black holes evaporate raises what I think

is the most profound question in the history of physics, certainly

over the last hundred years, and that's no exaggeration.

See, what happens if I set fire to this piece of paper?

With Stephen Hawking's equation written on it, I cause it

to evaporate away. Do I destroy everything?

Do I remove every piece of information, including

the equation from the universe when it burns away?

Well, the answer is no.

If I could collect every ash, every molecule of gas that burns off

into the atmosphere, then in principle I could reconstruct

the piece of paper and everything it contains.

Every piece of information on this piece of paper,

including Stephen Hawking's equation.

But can that be true for black holes?

The ultimate gravitational prisons? These objects in the sky

from which even light itself can't escape?

When they evaporate away, do they return the information

about everything that ever fell in back to the universe?

STEPHEN HAWKING: Black holes ain't as black as they are painted.

They are not the eternal prisons they were once thought.

Things can get out of a black hole,

both to the outside and possibly to another universe.

So, if you feel you are in a black hole, don't give up.

There's a way out.

If information somehow escapes from Sagittarius A*

as it evaporates away,

the implication is profound.

Black holes aren't tombs.

They're gateways.

We now believe that anything that falls into Sagittarius A*

will live on.

Not as a physical object,

but as information.

Escaping from the heart of darkness.

Encoded in the Hawking radiation in the far future.

The memory of all those worlds that fell into Sagittarius A*

over the entire history of the Milky Way galaxy is somehow

written in the ashes of the universe in the far future.

But the real treasure lies in the explanation

of how the information gets out from those eternal prisons.

Now, what I'm going to tell you is going to sound absolutely bizarre.

It's going to sound like science fiction, but here goes.

When the black hole has evaporated away, about half of it has gone,

the interior becomes, in some sense, the same place

as the distant Hawking radiation that was emitted aeons ago

that's out there in the far reaches of the universe.

It seems that space time wormholes open up between the interior

of the black hole and those distant parts of the universe,

and it's that that allows us to read the information inside.

Now, that is supposed to sound weird, and I should say that nobody

really agrees on the physical picture of what's happening.

But what everybody agrees on is this - the black holes

are telling us that our intuitive picture of reality

of space and time is wrong.

The idea that this place is close to this place

and that time ticks along is wrong.

There is a deeper picture of reality

in which space and time do not exist.

Our attempt to answer a seemingly simple question

about the fate of objects that fall into black holes has led us

to a profound and quite unsettling conclusion.

Space and time, concepts so foundational to how we experience

the world, are not fundamental properties of nature.

They emerge from a deeper reality

in which neither exist.

The thing about black holes

is that nobody really understands them.

So don't worry if you don't understand what I'm talking about

because I don't understand what I'm talking about,

and nobody else does either.

We're still a long way from fully comprehending the secrets

of black holes...

..but we are beginning to lift the veil.

Far from being a mere cosmic aberration,

Sagittarius A* is a part of our history and of our future.

Our black hole not only made us who we are today,

it's our teacher,

slowly revealing the deepest mysteries of the universe.

Secrets sealed away for so long

inside a place beyond forever.

The moral of the story is this.

Understanding the book of nature is hard,

and so the more of nature we observe, the more chance we have

of finishing the book.

Now, the strangest objects in nature by far are black holes,

and so I suppose it's not surprising that by peering over the horizon

and into the darkness, we have caught a glimpse of something

deeply hidden - the underlying structure of reality itself.

So if we want to understand the meaning of it all,

we can't restrict ourselves to the intellectually safe confines

of our planet.

We have to look out there to the universe beyond.

# Baby, you understand me now

# If sometimes you see that I'm mad

# But I'm just a soul whose intentions are good

# Oh, Lord, please don't let me be misunderstood... #

So of the seemingly endless zoo of objects in our universe,

from clouds of gas to planets to stars, galaxies, what have you,

black holes are probably one of the most fundamentally important

singular class of objects that we can study.

A place where the laws of physics literally break down,

and we have theories, but we can't really know what's happening.

So black holes present this remarkable invitation

to physicists, mathematicians, astronomers.

One of the best tools we have to study these exotic phenomena

is the Chandra telescope.

Chandra's kind of like a black hole hunter, finding them

near and far throughout the galaxy and the universe.

Just a few minutes away from the 26th flight of the Shuttle Columbia

with a crew of five.

I think a night launch is particularly exciting.

You have a go for start.

We have booster ignition and liftoff of Columbia.

You just see fire.

It lights up the night sky in the most beautiful way.

Columbia now has burned more than 2 million pounds of fuel

and weighs half of what it did at launch.

It's huge. Chandra is about the size of a school bus.

It's the largest telescope to ever be launched by the Space Shuttle.

SRV separation is confirmed.

You're stressed about the astronauts on board that are literally risking

their lives to help us get a better view of the universe.

When the main engines cut off, we're in zero G.

We separate the tank and we're orbiting the Earth.

And when we're sure that everyone is ready at mission control

and I go ahead and pull the switch marked deploy,

and you're looking at the deploy of the Chandra X-ray Observatory.

Chandra is an X-ray telescope,

which means that it can see the most energetic light

coming at us from the universe.

The telescope has to be outside the Earth's atmosphere

because the Earth's atmosphere,

thankfully for us, blocks out X-rays.

Otherwise, if... We'd just get fried.

The Chandra satellite, by rising above the atmosphere,

has a much clearer view.

Why is that so interesting for studying things like black holes?

Black holes can excite matter in their vicinity

to very high energies.

They can get atoms and parts of atoms whipping around

and by revving up those particles to very, very high energies,

they will radiate

so we can gather enormous amounts of information

about the immediate vicinity of a black hole.

When we look at Sagittarius A* today,

it's quiet and not doing very much.

But when we look at other supermassive black holes

in the universe, they're active.

So you can take Chandra and watch a black hole have a small snack,

maybe like a human might have a little biscuit in the afternoon,

and it's something like an asteroid

and there will be a small sort of X-ray signature from that event.

But you can also see a black hole have a really, really big snack,

and Chandra's may be able to witness that as well.

Chandra has witnessed the destruction of a star

by a black hole itself, right?

So this poor star wanders in to the black hole

that it rips the star apart, it shears it, right?

And then the corpse of that star,

this sort of spaghettified matter that starts spiralling around

the event horizon lights up in X-rays.

So to be witness to that, to observe the destruction of a star,

you know, in time, was just extraordinary.

It's just unbelievable.

There's this one pretty famous image that Chandra took called

the Chandra Deep Field South,

and it's the deepest X-ray image ever.

In that one data set, there's thousands of black holes,

like maybe 5,000 of them, if not more.

And it just kind of helps show you that they're all over the place

and there's so much more to discover.

Next time...

..we journey back to the cosmic dark ages,

exploring a time before the Big Bang...

..to answer the ultimate question.

How did the universe come to be?

Journey through the universe with the Open University

and learn more about stars, planets and galaxies with this free poster.

Order your poster by calling...

..or go to...

..and follow the links to the Open University.

# I'm just a soul whose intentions are good

# Oh, Lord, please don't let me be me misunderstood

# Don't let me be misunderstood

# I try so hard, so please, don't let me be misunderstood... #

Mach 1. Vehicle's now going supersonic.

Our universe is an enigma.

An endless, inexhaustible paradox.

It's largely...

..a dark, cold and lifeless ocean.

But within this ocean...

..there are islands blazing with light.

Galaxies.

Trillions of them.

Each one home to hundreds of billions of stars.

And around many of these stars, there are planets.

Alien worlds.

Each incomprehensibly strange.

There are trillions of planets in our universe.

And one of them...

..nurtured beings capable of contemplating this cosmic drama.

Miraculously improbable.

Brief candles flickering against the eternal night.

As darkness begins to fall, if you know that all those points

of light that appear one by one

in the darkening sky are distant suns,

then it's impossible not to be overwhelmed at the sheer scale

and majesty of it all.

The universe is infinite in all directions and

terrifying in all directions.

But if you can overcome your fear, then questions arise.

And surely the most profound question of all is, how did all

this come to be here?

That's a question that's defined much of human history, but it's only

in the last century or so that we've had the intellectual

and technical tools to interrogate nature directly, in search

of an answer.

And we've found that it looks for all the world like there was a first

moment in time, a beginning to the universe,

13.8 billion years ago - the Big Bang.

For all the world, but not quite.

Because we've begun to suspect that there's more to it.

And we've embarked on a heroic quest to search for and to explore

the time before the dawn.

I can see everything quite clearly. The light...

It has a stark beauty all its own.

Beautiful, beautiful...

For all the people back on Earth, the crew of Apollo 8

has a message that we would like to send to you.

In the beginning, God created the heaven and the Earth, and the Earth

was without form - and void.

And darkness was upon the face of the deep.

And God said, "Let there be light".

And there was light.

And God saw the light,

that it was good.

Since we first became conscious of ourselves...

..we've looked to the heavens, to those mysterious lights.

Searching for answers.

What is the universe?

How did it come to be?

And what is our place in the cosmos?

We sometimes doubt the creation stories that our ancestors told.

But those ancient myths conceal a profound truth.

The clues to the origins of everything

can be found out there.

In light...

..which ripples to us...

..from beyond the stars.

If we're going to dare to know about the origin of the universe,

then we have to have some evidence, and the connection

we have with the deep past is light.

You see, light travels very slowly on the universal scale, only 186,000

miles a second.

It takes light eight minutes

to journey from the sun to the Earth.

It takes four years for light to journey from the next-nearest star.

And that means we see that star as it was four years in the past.

So the further out into the universe we look, the further back

in time we look.

And because we can look way out into the distant universe,

we can look back towards the beginning of time.

Go ahead, Charlie.

Well, we have a go for release, and we're going to be a minute late.

OK, Charlie.

In the quest to find the origin of the universe...

..we need a time machine.

..Look good, and we'd like to go

to the next stage.

We concur, Charlie.

A telescope so powerful, that can peer out so far into the universe

that it can capture the most ancient light.

Telescope is released.

And carry us back...

..towards the dawn of time.

OK, Charlie.

The Hubble Space Telescope has taken us on an odyssey

through the universe.

Revealing it's god's...

..and monsters.

Our universe is a place of beauty...

..and terror.

Hubble has shown us visions of sublime creation...

..and images of awesome destruction.

Illuminating our journey backwards in time...

..towards the dawn.

The Orion Nebula, a stellar nursery.

Clouds of gas nurturing newborn stars in the Milky Way.

An image brought to us by light that left the nebula

1,300 years ago.

The pillars of creation.

Towering, delicate structures, light years tall.

7,000 years ago.

The Andromeda galaxy.

A glittering island of a trillion suns...

..two and a half million years ago.

A cosmic rose.

Galaxies colliding in a celestial dance.

300 million years ago.

But Hubble's voyage has taken us even further out into the uncharted

ocean of space.

Glimpsing countless ancient and faraway galaxies.

Wild and primitive shoals of stars.

Lighting the way to the primordial past.

Until finally,

Hubble approached the farthest shore.

A galaxy near the dawn of time.

This is a galaxy called GN-z11, and it is one of the most distant

galaxies we've ever seen.

This is light from some of the first stars in the universe.

It began its journey only

400 million years after the Big Bang.

And it's taken 13.4 billion years to reach us.

When you think about that.

This light journeyed through the universe,

and after nine billion years of its journey, the Earth formed.

And then, during the whole history of our planet, it completed the last

third of its journey, and entered our telescopes.

So this is an image from the edge of time.

GN-z11 was one of the very first galaxies, formed at a time

when the universe itself was taking shape.

Shortly after the Big Bang.

GN-z11 was a strange galaxy by today's standards.

25 times smaller than the Milky Way.

But filled with enormous, violent stars.

Lurking alongside these volatile giants...

..there were other things.

Delicate objects struggling in the maelstrom.

Some of the first planets in the universe.

These were strange, primordial worlds.

And over the horizon of one of them,

a sun rose.

Marking a new chapter in the history of the universe.

The beginnings of a relationship between stars and planets...

..that would,

billions of years later, on a faraway world...

..lead to the origin of life.

Now, we don't know when or where

the first dawn broke in the universe.

But what we do know is that

the first dawn was not the first moment.

The stars and planets had to come from somewhere.

So the first dawn was preceded by a long, dark night.

Astronomers call this era the cosmic Dark Ages.

If we continued to journey back in time,

we'd see shadows fall across the universe.

The galaxies would disappear.

The first primitive stars would be extinguished one by one.

And darkness truly would

be upon the face of the deep.

Here,

in the impenetrable gloom of the cosmic Dark Ages...

..our quest to understand the origins of the universe...

..would seem to end.

So how can we peer into the cosmic Dark Ages to explore the origin

of the universe?

Well, perhaps counterintuitively, the light from the stars

can still guide us, because that starlight has been travelling

across the universe for millions or even billions of years to reach

us, and information about the way the universe has changed and evolved

becomes imprinted in that starlight.

The stars have illuminated our voyage through time.

But their light can't guide us directly across the Dark Ages.

Instead, their light can be used to build maps of the universe...

..in space and time.

That allow us to navigate...

..towards the moment of creation.

And the most valuable light of all...

..comes from very particular stars in the spectacular swansong

of their lives.

Stars exist in a permanent state of conflict because the force

of gravity is relentless. Left to its own devices, it will crush

anything and everything, without limit.

But fortunately, other forces come into play. As the star

collapses, its core heats up and turns into a giant

nuclear fusion reactor.

Hydrogen is converted into helium. That releases energy, which creates

a pressure, which holds the star up.

But stars like our sun burn hundreds of millions of tonnes of hydrogen

into helium every second.

And although they are big, they're not infinite in size.

Stars, just like human beings, have a lifetime.

They are subject to the relentless march of time.

Now, for stars like our sun,

the collapse continues until it produces a new and exotic type

of star, known as a white dwarf.

White dwarves are strange beasts.

The fading remains of stars.

Super-dense, planetary-size cores, usually composed entirely

of carbon and oxygen.

Stars that were once a million times the size of our planet,

crushed to the size of the Earth.

Subjecting the carbon to extreme pressures.

And making white dwarves, in effect,

stellar diamonds.

These diamond stars are critically balanced, able to resist

the relentless inwards pull of gravity,

but only just.

And that can make them ticking time bombs.

In 2018, Hubble was in orbit.

The telescope focused on a galaxy far, far away.

Hunting for a distant white dwarf that we knew was coming to the end

of its extraordinary life.

For millions of years, the white dwarf had remained hidden.

Locked in orbit around a much bigger star.

A red giant.

As they circled each other,

the white dwarf's gravity drew in gas and plasma from the red giant.

The mass of the white dwarf increased...

..until it approached, a critical limit.

Known as the Chandrasekhar mass.

And surpassed it.

Triggering a colossal thermonuclear reaction.

The white dwarf detonated...

..In a gigantic explosion...

..called a supernova.

That millions of light years away...

..was detected by Hubble.

That white dwarf star or, to be more precise, the supernova

that it became, has a name.

It's called SN 2018 GV,

and even though it is 70 million

light years away, it is so bright that we could make a movie on it.

I mean, imagine that - this is a star the size of a planet

ending its life with a flash of light that's as bright

as five billion suns.

Now, although supernovas like these only shine

for a few days,

they cast a profound light out across the universe.

We've given a name to the sort of supernova Hubble saw.

They're called type IA supernovae.

And they're common enough to allow us to map the evolution

of the universe.

Type IA supernovae really are nature's gift to us.

Because they all explode in the same way,

that means that they all shine with the same brightness.

And that means that if we see one that's dimmer,

it must be farther away.

And that allows us to measure the distance to the galaxy

that contains the supernova.

And because they shine so brightly, we can see them tens of billions

of light years away.

That means that we can measure the distance to galaxies all the way

out towards the edge of the observable universe.

But there's other information encoded in the light.

When we look at the light from distant supernova explosions,

we see something very interesting and very surprising,

because the light from every single supernova that's not

in our neighbourhood is redder than it should be.

And the further away the supernova, the redder the light. It's called

the redshift.

Now, light has a wavelength.

And the longer the wavelength, the redder the light.

So the explanation is that during the time the light

has been travelling from the supernova to us, space itself

has been stretching, and that's stretched the light.

And that means that the universe

is expanding.

In our quest to find the origin of the universe,

this is a vital clue.

Because if the universe is expanding today,

then tomorrow, everything will be farther apart.

And it follows that, yesterday...

..everything was closer together.

So if we want to understand how it all began...

..we have to wind back time...

..through billions of yesterdays.

We have to go back to a time before the Earth and sun...

..to a time before the galaxies.

And, all the while, the universe is shrinking.

Getting ever smaller...

..denser and hotter.

Until we arrive at the most famous moment in the history

of the universe.

Our universe is a place of infinite variety.

There are galaxies of exquisite beauty.

Stars of stupendous power.

And planets.

Countless brave new worlds.

Galaxies, stars and planets are the things that make

our universe remarkable.

They are the things that make it more than a barren expanse.

How did a universe of light and life emerge from the cataclysm...

..of the Big Bang?

Unfortunately, we don't know.

We don't even know if the universe had a beginning.

But we do know a great deal about how the universe evolved

from a very different state a long time in the past.

We know that 13.8 billion years ago, this space that I'm standing in now,

and the space you're standing in now,

and all the space out to the edge

of the observable universe, containing two trillion galaxies,

was very hot and very dense and has been expanding ever since.

Now, that implies that way back, everything was closer together.

Everything was contained in a very small speck.

But how small was that speck?

And how did it come to be?

Well, we used to think that the universe emerged

in that state, very hot and very dense, at the beginning of time.

And we used to call that the Big Bang.

But now we strongly suspect that the universe

existed before that.

And in that sense, it's possible to speak of a time

before the Big Bang.

So what was the universe like before the Big Bang?

The first thing to say -

is that it was very strange.

There was no matter.

All that existed

was space-time, and energy, an ocean of energy.

Almost still.

But gently rippling.

Before the Big Bang, the universe

was a cold, alien, featureless place.

Picture it as a near-still ocean of energy, filling the void.

Although it contained no structures, that energy

did have an effect on space.

It caused it to stretch.

Not the gentle expansion we see today,

but an unimaginably violent expansion.

That expansion is known as inflation.

Think of a speck, a tiny, insignificant patch of space.

Insignificant, except that many billions of years later,

this spec would have grown to become our entire observable universe.

The speck expanded at a phenomenal rate.

An exponential expansion...

..that lasted...

..for just a few billion, billion, billion, billionths...

..of a second.

Now, the speck continued to expand until it was about the size

of this cave, and then inflation drew rapidly to a close.

And all the energy in that ocean, that was driving the expansion,

was dumped into space and formed the ingredients of everything

in our observable universe.

I mean, imagine that - a space about this size filled with enough

energy to form two trillion galaxies.

That's what we call the Big Bang.

So the Big Bang was not, as we commonly imagine,

some kind of explosion.

It was actually a transformation of energy

into matter.

And the fossilised remains

of these momentous events, the memory

of the rippling ocean of energy

that drove inflation, became imprinted

into our universe.

In fact, these fossilised ripples shaped our universe.

Influencing where each galaxy and star emerged.

Each planet...

..and moon.

But how do we know all this?

How do we know that there was a Big Bang?

How do we know that there were ripples in an ocean of energy

before the Big Bang?

The answer is...

Sept, six, cinq...

..that we've seen them. ..trois, deux...

Planck scanned the entire cosmos...

..looking for light.

Not light from galaxies or stars.

But light from the beginning of time.

LIQUID DRIPS

This is a photograph of the distant past.

It's the most ancient light in the universe.

This is light that's travelled for almost 13.8 billion years

to reach us.

It's a photograph of the entire sky, it's like the celestial sphere,

if you like. Every direction that we can look.

And it's been laid flat, so we can see it all.

It's called the cosmic microwave background radiation,

and it's an almost featureless glow.

There are no stars and no galaxies in this universe.

Now, you might ask the question, Well, if there are no stars

and there are no galaxies, then where's the light coming from?

The answer is the light is coming from the universe itself,

because this is only a few hundred thousand years after the Big Bang,

so the universe was hot.

So what you're seeing here is the afterglow of the Big Bang.

The most revealing thing about this picture

is the detail.

The variation.

This pattern is one of the most important discoveries

in all of human history, because it represents one

of the necessary steps in the story of how we came to be here.

See, that's still ocean of energy that drove the rapid expansion

of space during inflation, could not be entirely stellar.

There had to be ripples in the ocean.

It's a consequence of the laws of nature, as we understand them.

And those ripples in the ocean were imprinted into our universe

through the Big Bang, and emerged as those areas of slightly different

density in the young universe.

And then as the universe continued to expand and cool, the regions

that were slightly denser collapsed to form the first

stars and galaxies.

So without those ripples, we would not exist.

But there's one more extraordinary thing about these ripples.

And that's the fact that we predicted them

before we knew they existed.

And then we ventured into space to test our theory.

Planck's observation of the

afterglow of the Big Bang is strong evidence

for our outlandish creation saga,

the story of the speck,

the ripples, and inflation.

These ripples, then, are the seeds of our creation, and we dared

to guess that they exist,

from our vantage point here on a small planet 13.8 billion years

after the moment of creation.

And then, because we're scientists,

we decided to launch a spacecraft out into space and capture

the oldest light in the universe.

And we saw that our guess was correct.

We dared to imagine a time before the dawn, and we proved

that our creation story is not a myth.

So here is the creation story...

..as told by science.

In the beginning, there was an ocean of energy

that drove a rapid expansion of space, known as inflation.

There were ripples in the ocean.

As inflation ended,

the ocean of energy was converted into matter...

..by the Big Bang.

And the pattern of the ripples was imprinted into our universe,

as regions of slightly different density in the hydrogen and helium

gas that formed shortly after the Big Bang.

The denser regions of gas collapsed...

..to form the first stars...

..and the first galaxies.

And nine billion years later...

..a new star formed,

in the Milky Way.

The sun.

The star was joined by eight planets...

..including...

..Earth.

And nearly 13.8 billion years after it all began, we emerged...

..blinking, into the light.

in that eternal silence where it floats, is to see ourselves

as riders on the Earth together, brothers on that bright loveliness

in the eternal cold.

Brothers who know now they are truly brothers.

We all have moments of wonder.

We all dream.

Our thoughts float free, soaring across the Earth and out

into a canopy of stars.

In our most reflective moments,

I think we all understand that small though we are,

we are connected to the universe.

We are collections of simple atoms.

But atoms arranged remarkably.

With the urge to explore the universe and to comprehend it.

And celebrate our own place in this great cosmic saga.

And if we follow that saga back, it takes us on a pilgrimage.

To a time before the dawn...

..and to strange ripples that existed

in a universe before our own.

I think we all must wonder about the meaning of it all.

What does it mean to be human?

Why do we exist?

Why does anything exist at all?

These do not sound like scientific questions.

They sound like questions for philosophy, or theology, even.

But I think they are scientific questions because they're questions

about nature, they're questions about the universe. And the way

to understand the universe is to observe it.

I mean, we've seen ripples in the most ancient light

in the universe, laid down by events that happened before the Big Bang.

We've seen billions of galaxies written across the sky in a giant

cosmic web, and we've seen thousands of planets orbiting around distant

stars, worlds beyond imagination.

Now, the lesson, to me, is clear,

we won't answer the deepest questions

by being introverted, by looking inwards.

We will answer them by lifting our gaze above the horizon and looking

outwards into the universe,

beyond the stars.

We used to look to the sky and see only questions.

Now, we're beginning to see answers.

Hubble is a very special telescope, it's kind of like the celebrity

telescope, and for a really good reason.

It was the first time that we were able to launch such

a powerful, large optical telescope into space.

The Earth's atmosphere kind of blurs out lots of our images.

And so by putting the telescope in space, we get these precise,

crystal-clear images of our universe.

Three, two, one and liftoff of the

Space Shuttle Discovery, with the Hubble Space Telescope.

Our window on the universe.

The feeling that you get when the space shuttle takes off,

there's just the sort of, the sound and the vibrations.

It's just incredibly awe-inspiring.

The rocket boosters have done their job.

Go ahead, Charlie.

We have a go for release, and we're going to be a minute late.

We were all sort of sitting on the edge of our seats, waiting

for the very first images where Hubble is showing us

what it can see in the universe.

And that turned into an unexpectedly long wait.

Engineers have discovered that the giant telescope has a

warped mirror, which means the

images sent back to NASA are distorted.

We had this very, very precisely engineered mirror, but it

had been very precisely engineered to the wrong shape.

For the first three years in the life of the Hubble,

it wasn't producing the wonderful

images that everyone had expected.

The solution was the same solution to the fact, that as a kid,

I couldn't read the blackboard.

The solution was basically to fit the telescope with corrective optics

so something analogous to spectacles.

And we have a go for main engine start.

..Three, two, one.

And we have liftoff, liftoff of the Space Shuttle Endeavour,

on an ambitious mission to service the Hubble Space Telescope.

It's kind of amazing that we have to be able to position

this optical equipment to an accuracy of better

than a millimetre, something that you'd have trouble doing even

on the ground in your bare hands.

Firm handshake with Mr Hubble's telescope.

Copy that.

The Vice President and I wanted to call you and congratulate you on one

of the most spectacular space missions in our history.

And when Hubble opened its eyes after they were corrected, the views

that we were able to get from that telescope changed forever

the way we understood and

visualised the universe that we live in.

CHEERING AND LAUGHTER

The pictures are remarkable.

The trouble with Hubble is over.

It's really hard to remember what it was like before

we had the Hubble Space Telescope.

We've gotten so used to these extraordinary photographs

of the near, of the far, of the very, very far.

I think any time I look at a Hubble image, my mind gets blown

a little bit.

I was the kid that had, like, printouts of Hubble images

in their locker.

Anybody, whether they have the heart of an astronomer or the soul

of a poet, they're going to find things in the images from Hubble

that just appeal to them from the point of pure wonder.

Hubble has not only done the things that people expected and hoped

it would, but it's actually done a lot of things that nobody

would have dared to dream of.

One of the biggest discoveries that came from using the Hubble

Space Telescope is that not only is our universe getting bigger,

it's not just expanding and stretching, it's actually

getting bigger, faster.

We can well imagine that the universe is going to continue

to expand and get so big that eventually the galaxies

will just disappear.

They'll, they'll, be so far away from us and moving so rapidly,

that we have no hope of seeing any light from them.

And that's a real possibility for what could happen in the future.

We still have these mysteries of what's really driving

this new phase of accelerated expansion, and we're building

new tools to try to refine those questions.

The Hubble telescope, which was a marvel for its time,

is really far behind what we would design today.

It will be completely outclassed by the next generation telescope,

the James Webb Space Telescope, which will see even

deeper than Hubble.

And that will give us unprecedented detailed views. We can use it to see

through some of the very dense, murky dust clouds and actually see

stars in the process of forming.

We also can use it to look further and further back in time.

That's going to be a very, very exciting story,

which is going to unfold, I think, within the next three or four years.

Hubble is still king because it's still a big observatory

in comparison to what we've had in space before. Hubble is a unique

instrument for making discoveries that no other telescope

could possibly have made.

I think when you think about an image of space, when you think

about space, you think of a Hubble image.

Journey through the universe with the Open University, and learn

more about stars, planets and galaxies, with this free poster.

Order your poster by calling 0300 303 5746.

Or go to

bbc.co.uk/theuniverse, and follow the links

to the Open University.