How the Universe Works - Eleventh Season

A small black star floats through space.

This is the Sun, billions of years in the future.

It's all that remains of our solar system,

the sole survivor of a dramatic history

of elegant beauty and extreme violence.

Just because things look really nice and serene

now doesn't mean it's always been that way.

There are a lot of planets that could have made it

but didn't, and we just happen to be

one of the lucky ones that did.

The players in our solar system's story

are more tangled up than we ever imagined.

The more we look at this stuff,

the more we realize that everything affects everything

else, including us.

How did we go from a vibrant family of planets

orbiting the yellow sun to a lone,

dead zombie star?

It's an old familiar story.

A bunch of planets orbit a yellow star

in a quiet suburb of the Milky Way galaxy.

But it's not the whole story.

Over the past decade, our vision of

our solar system has been completely revamped.

Think of the solar system as

an old-fashioned mafia crime family.

The sun is the Don, his quarreling children,

the planets.

Their story, like any good mob movie,

is an epic tale of empire building,

sibling rivalry, greed, and ultra violence.

The origin of the solar system was chaotic

and violent... Planets colliding,

planets even changing places.

Now, a shift in our understanding reveals

a tale of tangled alliances between family members.

Just think about how much our view

of the solar system has changed.

The planets used to be so far away from each other,

and of course, they had nothing to do with each other.

And now, the history is all about the interaction.

So the idea that everything is just

its own world and doesn't interact is completely wrong.

We like to think of astronomy as looking up,

looking outward, away from ourselves.

But the more we do that, the more we realize how

connected we are to everything out there.

You probably have some material in your body from

pretty much every world that

ever existed in the solar system.

Like any good mobster movie,

our story starts with the humble rise of the Godfather.

In this tale, that's the birth of the Sun.

But exactly how that happens is a mystery.

When we're trying to figure out how the solar system began,

you know, we don't have a time machine.

So what can we use to find out about how it formed?

The solar system has the answer,

its own time machines... Meteorites.

Meteorites are pieces of the solar system from

the distant past, and they've remained unchanged since then.

So they're like little time capsules.

They're like fossils from before

our solar system even formed.

By studying them,

we can really study what was happening and what was going

on in the very early days of our own solar system.

2020...

Scientists study ancient material trapped inside

a meteorite found in Murchison, Australia.

The Murchison meteorite contains tiny crystals called

presolar grains that predate our sun.

And trapped within them is evidence of

the history of the formation of our solar system.

The presolar grains are made up of

elements like silicon that form inside giant stars.

When these stars die, they blow out

huge clouds of gas and grains of dust.

The term presolar grain doesn't sound very romantic,

but actually, we might call those stardust,

because these materials are things that were

made in stars that no longer exist.

The Murchison meteorite contains grains

from at least 46 different stars.

What the Murchison meteorite tells us is that

the material that came together

that formed our solar system had its origination in

dozens of different stars.

These stars died and blew out all of these materials.

And then created this huge cloud of gas and dust

called a nebula.

The sources of the material in that cloud

could come from one of a number of places.

The material from lots of stars'

atmospheres could be mixed in there.

In the mix were the ingredients to build

the solar system,

but we don't know what triggered

the gas and dust to form the Sun.

A 2020 study may have the answer.

One of the coolest things we've discovered

in the last couple of decades about the Milky Way

is there's a giant stream of stars that's

stretching across virtually the whole sky.

These stars were not born in the galaxy.

They're not from here.

If not from our galaxy,

then from where?

We think these stars actually came from

the Sagittarius Dwarf galaxy, which orbits the Milky Way.

Over five billion years ago,

the Sagittarius Dwarf galaxy wanders

too close to the Milky Way.

Our galaxy's powerful gravity drags Sagittarius towards it.

The galaxies collide.

As this is happening,

the Milky Way is tearing Sagittarius apart,

ripping stars out of it.

This is truly intergalactic cosmological drama at play.

This collision shakes up the Milky Way.

When a body passes

through the disc of our galaxy, it's

gonna set off ripples, and that's going to compress

the gas clouds, and that's gonna create star formation.

The Sagittarius Dwarf smashing into the Milky Way

is like dropping a boulder into a pond.

It sets out ripples of density,

and it disturbs everything in the galaxy,

but it doesn't disturb everything equally.

It causes some clumps of dust

and gas to start accumulating together.

The disruption in one galactic zip code leads

to new activity in others across the Milky Way.

The ripples trigger gas and dust left over

from the dying stars to split into clumps,

sparking a frenzy of star formation.

Look, if you were an observer,

suddenly, out of these little clumps of gas

come bright ignition sparks all at once.

If you were to stand there long enough,

watching this stellar nursery,

it might look kind of like a field at night

with fireflies blinking on.

Perhaps the Sun formed in this starburst.

The passage of the Sagittarius Dwarf

through our galaxy correlates

in time to the formation and birth of our sun.

So maybe our solar system came about as a result of

the Sagittarius Dwarf passing through our galaxy

over five million years ago.

Of course, we don't know for sure if this is what triggered

the formation of our sun, but the timing does fit.

4.6 billion years ago,

part of the cloud seeded with

material from dying stars grows denser,

until it gets so massive, it collapses.

As the gas cloud collapses,

it gets hotter and hotter and spins faster and faster,

forming a dense core at its center.

The core is the protostar that will later become our sun.

The protostar drags in more and more gas and dust,

creating a region of materials spinning around it

called the protoplanetary disk.

As the Sun builds up more mass,

it's getting compressed gravitationally, and so the core

is getting hotter and hotter and hotter.

The densities are increasing.

The new Don, the head of our solar mobster family,

immediately reveals a ferocious nature,

blasting out supercharged jets of radiation.

The early sun was not the calm, glowing orb

that we see in our sky today... It was far more chaotic.

It's sort of like in its toddler phase.

It was acting up all the time.

It has all of this energy that pushes material off of

the surface and launches it into

what we call the solar wind.

The blizzard of particles races out

at over a million miles an hour.

It smashes into the protoplanetary disk

and blows the gas away.

At the same time, the Sun's core heats up to 18 million

degrees Fahrenheit,

triggering the fusion of hydrogen into helium.

And that releases a tremendous amount of

energy that eventually works its way back to the surface of

the star and comes out as light.

Finally, the Sun becomes the recognizable

sun that we see in our sky today.

The sun is now the Godfather,

pulling the strings on the solar system.

The young Don's rise to the top

triggers a power struggle with its willful children,

the planets.

It's a brutal fight for survival.

4.6 billion years ago,

our mob family rises in a quiet suburb of the Milky Way.

Its Godfather, the Sun, forms from a collapsed

stellar nebula.

The greedy star scarfs down most of the cloud of gas