Universe

Subs by KalEl82

I can see everything quite clearly.

It has a stark beauty all its own.

# See me when I float like a dove

# Skies above...

Magnificent desolation.

- Beautiful view. - Isn't that something?

# Take me away #

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'd 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 prisons from which even light itself can't escape.

But 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.

And we copy at 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 14, 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,

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.

Twenty 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 burnt blue in 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 matters so densely it tears a hole in the universe.

In the vicinity of a black hole,

space and time behave in very counter-intuitive ways.

In fact, this river provides a beautiful and surprisingly accurate analogy.

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 can imagine I can 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 spacetime.

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

stars, and planets, and galaxies,

curve and distort 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.

And fortunately, 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 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 disk...

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 gluttonous period

that marked 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.