All language subtitles for HTUW S07x05 Secret World of Nebulas

SUB BY : DENI AUROR@
https://aurorarental.blogspot.com/

All across our galaxy,

stunning clouds of gas and dust ... nebulas.

They contain secrets of the cosmic circle of life,

the birth and death of stars, planets, and us.

These things are really cradles of creation.

You are intimately related to the nebulas.

You are a nebula come alive.

The story of how our solar system formed

starts with a nebula.

If you want to build a solar system,

you're going to need a nebula.

Look around you.

Everything you see everywhere was once inside of a nebula.

Now scientists are pulling back the veil...

Opening our eyes to the true expanse of our universe.

...Solving the riddles

of these engines of creation.

There are mysteries waiting inside

that we haven't even guessed at yet.

captions paid for by discovery communications

The milky way ...

a spiral galaxy full of regions

of gas and dust called nebulas,

and everyone has their favorite.

Bullock: I really like the horsehead nebula.

It just looks awesome.

The cat's eye nebula has always been really captivating to me.

My favorite nebula is the Orion nebula.

The Orion nebula is perhaps the best place

to understand the evolution of stars,

and it's right here in our own backyard.

The Orion nebula is maybe one of the most famous nebulas

because you can go outside at night

and see it with your own eyes.

Humans have been observing

this fuzzy patch of sky for centuries.

The Maya of central America called it

"the fire of creation".

The Maya were more right than they knew.

Almost every part of the life cycle of a star

you can see in a nebula.

Sutter: We can't understand the life cycle of stars

without understanding the life cycle of nebulas.

They are intertwined.

Orion has it all,

from massive stars on the brink of death,

to newborn stars swaddled in gas.

Sutter: You see the intricate wisps of material,

the thin veils enveloping newborn stars,

pillars colliding into each other.

You see stars plowing through clouds of gas.

You see this frenzied hive of activity

operating right before our eyes.

In 2018, using new data,

NASA creates a groundbreaking 3-d visualization

of Orion's interior.

For the first time in history, we have the right tools

to actually explore the hearts of these nebulas.

Stricker: It was already beautiful to begin with,

but now we have even more vivid images to really appreciate

how great of a structure this is.

At Orion's heart lies a cluster of young stars.

Together, they blast out charged particles and solar winds,

blowing open a gap at the center,

creating a window inside.

We actually see the structures and the volume.

We can actually see the processes happening

right before our eyes.

The cluster's intense starlight

energizes the surrounding gas,

causing it to glow pink and blue.

The pinks come from light

emitted from hydrogen atoms in the nebula,

glowing like the gas in a neon tube.

The blues tend to come from the light from the hot,

new stars reflected off of dust particles.

These hot, new stars

illuminate the Orion nebula,

but they were actually born in the dark.

One particular type of nebula is a dark nebula,

and basically that's when the concentration of dust

is a lot greater.

Dense clouds of dust

block out visible light from the stars behind,

creating shadowy shapes like the horsehead nebula.

This nebula is so large and dense, it has enough mass

to make about 30 stars the size of our sun,

and now astronomers can peer inside.

Only recently have we been able to start doing this...

...thanks to detectors that can see light in the infrared.

The infrared allows us to sort of see

through the dust of a nebula

and see what's going on deep in its heart.

Humans can't see infrared light,

but we can feel it as heat.

Infrared detectors tell us these dark, star-forming clouds

are cold, hundreds of degrees fahrenheit below freezing.

But deep inside are hot spots.

Sutter: If you look at it with infrared, you see,

"ah, the signature of incredible densities

and incredible temperatures ...

the signs that a new star is being born."

A knot of matter comes together

under the force of gravity.

As it grows, so does the gravity.

It pulls in more gas, growing bigger and bigger.

That gets very massive, very dense, and very hot.

Eventually it gets high enough pressure and temperature

in the center of that object that you ignite fusion.

A star is born...

...one of the hundreds of billions

that make up our galaxy,

the latest in a stellar production line

going all the way back to the dawn of time

and the very first nebula.

Bullock: If we want to unravel the history of the milky way,

we want to start in the beginning,

and that's the big bang.

13.8 billion years ago,

the universe sparks into life.

At first, it's pure energy.

But over 300,000 years,

that energy cools into hydrogen and helium gas.

Back then, the entire universe was one enormous cloud.

The essential ingredients of our universe spread

as the universe expanded.

And so the universe started as one giant nebula.

Over time, the primordial nebula

starts to collapse

and fragment into smaller clumps.

These regions become so dense, they collapse into discs

with super-hot balls of gas in their cores.

¶¶

the first stars ignite.

They start out as nearly pure hydrogen,

but as they age, they make other, heavier elements.

Stars forge new elements. That's what they do.

The very definition of a star is in its core,

it's fusing hydrogen atoms into helium

and releasing energy.

But many of those first simple stars were massive,

and massive stars don't live for long.

They burned through their supply of hydrogen incredibly rapidly,

and they burned themselves out,

and they died after a few million years.

They go out with a bang...

¶¶

...an explosion that releases more complex elements

back in to the primordial nebula.

Straughn: After that first generation of stars

started to form,

there was this huge burst of new elements that formed

and that were dispersed throughout the universe

to be able to form that next generation of stars.

As the second generation of stars lives and dies,

it adds even more ingredients to the cosmic mix.

Sutter: The next generation of stars fuse more elements,

exploded, died, spread the material,

new generation of nebula, new generation of stars,

each generation having more and more elements

in the periodic table than the last.

And around 300 million years after the big bang,

our galaxy ... the milky way ... takes shape.

The galaxies like the milky way formed out of,

essentially, a proto-galactic nebula,

some gigantic gas cloud that collapsed down

and formed our galaxy.

There is a rich cosmic symphony

playing back and forth between stars and nebulas,

and we now know that we are a part of that symphony.

Eventually, our element-rich sun is born.

We think that our sun is a third-generation star,

so it was actually a nebula, a star, a nebula,

a star, a nebula before it became our sun.

It took around 10 billion years

to create a cosmic mix of elements

rich enough to build planets and life.

Carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur.

These are the key ingredients to life as we understand it,

and those need to be made in stars.

These elements are created

during the life of a star,

but it takes an incredibly violent process

to liberate them into the cosmos...

...an event that can be seen clear across the universe ...

a supernova.

The most beautiful nebulas in our galaxy

are born out of incredible violence ...

the deaths of giant stars.

Some of the most colorful nebulas in our galaxy

are remnants of supernova explosions,

things like the crab nebula,

cassiopeia a, also the veil nebula.

Those all happened when a giant star exploded violently.

The crab nebula was once a massive star,

with around 10 times the mass of the sun.

¶¶

in its core, that star crushed atoms together

to form heavier elements,

a process that releases huge amounts of energy.

A massive star can fuse heavier elements,

and those heavier elements into even heavier elements

until it gets to iron, and when it gets to iron,

that's when things go bad really fast.

Iron atoms are so big that fusing them

takes up more energy than it produces.

The core starts to collapse on itself,

setting off a catastrophic explosion...

¶¶

...blasting elements out into space.

When a star goes supernova,

it violently rips itself apart,

and all of the material of the star

can be spread across light-years.

We call this, rather obviously, a supernova remnant nebula.

Now you have a nebula filled

with all of these interesting chemicals.

All of those are illuminated

by the energy of the supernova explosion.

Supernova remnant nebulas

glow brightly in many different colors.

The colors in a nebula are kind of like a fingerprint

or a DNA test of the elements inside.

Every atom has a shell,

a cloud of electrons that orbits around its nucleus,

and as those electrons change energy levels,

the frequencies of light

associated with those energy changes

are emitted into space and contribute

to the broad spectrum of colors that we see.

Sutter: So, we can look at a distant nebula, and we can say,

"it's this much hydrogen, this much helium,

a little bit of platinum.

Oh, we got a lot oxygen in that one."

The colors of a nebula reveal the elements created

during a star's life and death.

But a nebula's shape can reveal what happens after a star dies.

You would think that one exploding star

would be pretty similar to every other one.

They would make the same sort of nebula.

And then you see the crab nebula,

with this beautifully complex shape ...

all of these different arcs and whirls of gas and dust.

Something must be shaping it from the inside.

Within the crab nebula

lurks a stellar corpse called a pulsar.

Pulsars are a kind of neutron star,

a ball of super-dense matter.

They're born from the death of massive stars.

This is the leftover core of the star that exploded.

This collapsed down and formed a very tiny ball of neutrons

and a little bit of normal matter that's very, very hot

and has a very, very strong magnetic field.

This pulsar is spinning

at around 30 times a second...

...blasting out beams of radiation

that sweep through space

like a frenzied cosmic lighthouse.

And the pulsar in the crab nebula doesn't just emit light.

It's also blasting out a wind of charged particles.

The gas cloud itself around it is the pulsar wind nebula.

So, it's taking all that leftover stuff

from the supernova

and blowing it out into that expanding cloud.

The pulsar winds plow through the surrounding gas,

creating the twists and folds of the crab nebula.

¶¶

supernovas create the elements.

Their winds spread them throughout the cosmos,

forming new nebulas,

nebulas that might form a solar system like ours.

The nebula is essentially the starting point

of the recipe for the solar system.

So, it's got all the ingredients,

all of the chemicals, all the gasses,

all that we see in our solar system today.

Think about the major elements that make up the planet earth.

What happened to bring all that together?

How did a gassy cloud of elements

become our planet and our sun?

What turned a nebula into our solar system?

Once upon a time,

there was no sun, no solar system, no us.

Just a cloud of gas and dust ... a solar nebula.

Sutter: We are here today because billions of years ago,

there was a nebula containing all the necessary ingredients.

Wadhwa: Everything that we see in our solar system today,

that was all part, originally, of the cloud of gas and dust

that was our solar nebula.

Almost five billion years ago,

a solar nebula was prepared to give birth to our sun.

So, we have, billions of years ago,

our solar nebula cloud of gas and dust,

and it's hanging out, but it's unstable.

What tips the balance

to turn a cloud of gas into solid objects?

Something has to change.

Inside a nebula, something has to trigger the formation

of stars and planets, and that remains a mystery.

So, what's the answer

to this 5-billion-year-old mystery?

¶¶

there are two theories.

Both start with fossils ...

fossils that make their way

from the edge of the solar system towards earth,

break through our atmosphere, and find their way to us.

Meteorites are really important for us to understand and study

because they're time capsules

to when the solar system was basically first forming.

Meena wadhwa curates one of the largest collections

of meteorites on the planet.

These rocks hold a pristine record

of the very early history of the solar system.

Wadhwa: There was nothing else around in the solar system

before these rocks were formed.

There was no earth, there were no other planets.

It's mind-blowing.

The first solid objects

form out of a cloud of dust surrounding our newborn star.

Asteroids and meteorites forming at the same time contain

the chemical fingerprints of our solar nebula.

They actually contain some of the oldest materials,

oldest solids that condensed from the cloud of gas and dust

as our solar system was forming.

And so, they came together and formed

this big rock that you see here.

In 2017,

researchers analyzing the composition of a type

of rocky meteorite called chondrites

find a clue about how our solar system was formed.

There might be, in fact, a smoking gun

somewhere in the chemistry of these rocks

that could tell us about what exactly happened

and how our solar system was formed.

This smoking gun is a radioactive element

called iron-60,

and it's thought to be created only in supernovas.

If you have a nebula which is about ready

to start forming stars

and a supernova goes off next to it,

that supernova is going to dump

all those heavy elements into that gas cloud,

but it's also going to trigger the formation of stars

by slamming into that gas and compressing it.

A nearby star goes supernova.

The shock wave strikes our solar nebula,

injecting it with iron-60.

But the collision starts a runaway gravitational collapse

in the core of the nebula.

The gas cloud clumps together, becoming hot and dense.

Our sun is born.

Stricker: As the sun is forming,

there's basically a cloud of junk all around the sun,

and as it orbits the sun, it kind of accretes

or sticks together and grows into these balls.

Over the next hundred million years,

these balls get bigger and bigger,

forming asteroids, moons, and planets.

All the planets in our solar system

seem very different.

Some ice giants, some gas giants,

some rocky bodies.

But, in fact, all of these planets

came from the same pre-solar nebula.

And on one small planet,

the right cocktail of elements gave rise to us.

Everything ... every atom in our bodies ...

was once part of the pre-solar nebula.

The theory that a supernova

nudged our solar system into existence is compelling,

but not everyone agrees.

Sometimes, the biggest arguments among scientists

are caused by the littlest things,

and in this case, I'm talking about little,

tiny radioactive atoms.

In 2017, studies reveal

other meteorites contain

a different radioactive signature ...

a rare isotope of aluminum called aluminum-26.

That's a rather odd atom

that is not formed very easily in supernovas,

so that had to come from somewhere else.

That somewhere else is a rare type of giant star

40 to 50 times the mass of our sun ...

a wolf-rayet star.

Stars can be very weird,

and the very massive stars are incredibly weird.

The largest type of star that we've seen

is what's known as a wolf-rayet star.

Wolf-rayet stars burn the hottest of all stars,

producing heavy elements

like aluminum-26 during their short lives.

These are massive and hot and luminous,

and they blow off a tremendous wind.

This stellar wind

ejects tons of matter from the star

into the surrounding space, creating a bubble structure.

Scientists see this process at work in the bubble nebula,

7,000 light-years from earth.

In the middle of the nebula

is one of these giant stars

with a massive stellar wind, high-energy particles,

radiation, and just like the name suggests,

it's blowing a bubble in the larger nebula around it.

The walls or shell of the bubble

are dense and full of matter.

The stellar wind pushes more and more matter

into the shell...

...until this material collapses under its own gravity

and condenses into stars.

It's entirely possible

that what we're seeing in the bubble nebula

is what happened here 4 1/2 or more billion years ago

to form the sun and the planets.

If our solar system formed

within a wolf-rayet bubble nebula,

it would explain why so much aluminum-26

is present in meteorites.

But the jury is still out.

What we do know is that our story

began with the collapse of the solar nebula.

But one day, our star will die.

Will the sun turn into a stunning nebula,

or will it just fade to black?

Nebulas make stars.

Stars make nebulas.

The most massive stars do so in violent supernovas.

But 99% of stars aren't big enough to go out with a bang.

Some will just burn themselves out.

But others can create beautiful nebulas

with the misleading name planetary nebulas.

From a distance, they look like planets,

but really, they're the ghosts of stars.

When stars like our sun begin to die,

they bloat up into what we call red giant stars.

As a sun-sized star reaches the end of its life,

its core gets hotter and hotter.

As it heats up, the surrounding gas expands,

transforming the star into a red giant.

It gets so big, its outer layers

are no longer held in place by gravity.

The outer layers of that star begin to drift away.

They kind of lose touch with that central core in the middle,

and they just begin to blow into beautiful shells,

beautiful colors, beautiful shapes.

We call these dying stars planetary nebulas.

We've discovered

over 3,000 planetary nebulas in our galaxy.

Some look like an hourglass or it looks like an owl

or a clown or a sphere or a doughnut.

But if they're all the ghost

of the same type of stars,

why do they look so different?

If you have a star that's just sitting there, no planets,

nothing else around it,

it's going to blow off its wind in a spherical shell.

And so, if you see a planetary nebula like that,

it looks like a soap bubble in space.

But only 20% of planetary nebulas

have this perfectly symmetrical bubble shape.

Most of them have these weird shapes.

They can be two loaves

that looks something like two squids kissing.

All kinds of different shapes to these things.

Experts think

the strange shapes of these planetary nebulas

may be linked to how a star dies.

And now new research may reveal the fate of our own star.

Will we be a beautiful, bright planetary nebula,

or will we just fade away into darkness?

For the first time now, we think we may have the answer.

It's a long-running debate.

Is our sun big enough to form a spectacular nebula?

It's kind of a funny coincidence.

The model shows that you need a certain mass

to make a planetary nebula.

By coincidence, the sun is pretty much right on that limit.

The new data suggests

that our sun is going to go out in style.

As the sun dies, it'll expand into a red giant,

filling up the sky.

We're used to our gentle yellow sun

coming over the horizon,

so imagine a giant, bloated, brilliant red glowing ball

coming over the horizon for the sunrise.

The expanding sun engulfs Mercury,

then Venus.

It'll cook the surface of the earth,

turning it into a molten hell.

Straughn: So, the sad news is,

is that once the sun expands as a red giant,

it will absolutely boil away the oceans on the earth,

life will no longer be sustainable.

It's like sticking your head in an oven set to broil.

It's not like it's going to be a fun time on the earth.

Some think it could even mean

the destruction of the planet.

We think the sun will eventually become large enough

to swallow up where the earth is now.

So, instead of there being a sunrise and a sunset,

we're going to find ourselves inside the sun.

¶¶

The sun sheds its outer layers,

ejecting over half of its total mass,

revealing the stellar core.

And so, when we look at this core,

which is now called a white dwarf

about the size of earth, they're very hot.

Like hundreds of thousands of degrees.

This white-hot core radiates U.V. light and x-rays.

These hit the outer layers of gas

and turn them into brightly glowing rings ...

a planetary nebula that will shine for about 10,000 years.

One thing is for sure, and that is the solar system,

when the sun turns into a planetary nebula,

is going to look a whole lot different than it does now.

It'll be unrecognizable.

The planetary nebula will mean

the end of the solar system as we know it.

The sun will eventually die away and unravel itself

back into space.

But then the cycle begins again.

This is not just an ending, it's also a new beginning.

It's going to provide the ingredients

that will foster yet a new solar system.

As one solar system dies, another solar system is born.

So really, this is the cosmic cycle of life.

Nebulas always signal change in the universe,

intimately linked with star birth and star death.

Now new observations reveal

that some of our favorite nebulas are also dying.

Could the famous pillars of creation be dead already?

Deep inside the eagle nebula

is a dense region of cold molecular gas,

perhaps the best-known image in all astronomy ...

the pillars of creation.

One of the images that really changed things

was the pillars of creation,

and it was an image that was very evocative.

It really made me feel very emotional.

The pillars are five light-years across

and silhouetted by the light from a nearby star cluster,

and it was these stars

that carved out the shape of the pillars.

The surface of these stars are energetic and boiling

and constantly streaming particles off of them.

10,000-mile-an-hour stellar winds ravage

the surrounding gas clouds.

Sutter: Eventually, they completely dissipate

their surrounding nebula.

As the nebula disappears,

columns of thicker, denser clouds survive,

but for how long?

When you look at these beautiful hubble images

of the pillars of creation, the eagle nebula,

you see some blue, very diffuse gas

around the pillars themselves,

and this is a clue as to how the pillars formed

and how they're going to change over time.

This hazy blue gas is actually super-heated material

evaporating off the pillars themselves.

Nearby stars are slowly eroding the pillars.

This is similar to how weather erosion works here on earth.

Think about monument valley.

You have these amazing stone pillars

and really unlikely shapes coming up out of the ground.

Well, those are denser areas of rock

that used to be covered up by soil and sand.

Over millions of years,

that lighter material was blown away,

exposing the denser rock underneath,

and that's exactly the same thing that's happened here.

This process is ongoing.

Nebulas like the pillars are constantly evolving.

Bullock: The thing you keep in mind

about the pillars of creation

is this is actually a pretty transient feature

in the life of the galaxy.

It's not going to last forever,

and in fact, over the course of time

even that we've taken images with the hubble space telescope,

we've seen it change.

When astronomers compared new data

to the original hubble image from 1995,

they discover a jet blasting out of the nebula

at 450,000 miles an hour,

extending 100 billion miles into space.

What could be the source of all this energy?

These jets are associated with the moment a star turns on.

The stars being born inside of the pillars

are basically eating their way out.

They're eating up this material,

and then they're going to blast it away.

Newborn stars are a lot like little kids

on a sugar rush.

They gorge on gas, then spin out of control.

But stars also have a magnetic field.

That magnetic field is rapidly rotating.

It's sweeping up this material around it

and shooting it out in two jets

going out of the poles of the star.

Jets and stellar winds

are destroying the pillars of creation from the inside out.

What's more, some of these baby stars are growing so fast,

they could soon reach the end of their short, violent lives.

When stars die, they send shock waves,

high-energy radiation, particles.

Supernova explosions like these could blow

the pillars to pieces.

Some have already suggested that the pillars may have

already been destroyed thousands of years ago.

Straughn: Eagle nebula is about 7,000 light-years away,

and so we are literally seeing the eagle nebula

as it was 7,000 years ago, not as it is today.

It's a sad fact of life.

Nebulas are destroyed by the stars they create.

That's happening all the time.

Everything changes.

Our most famous, favorite nebulas don't exist forever.

And it might seem really sad,

but this is just how the universe works.

It's a transitory state.

It's something in the act of changing.

Where today we see pillars of creation,

in the future, they'll just be clusters of stars.

But this eternal recycling of gas and dust

into stars can't last forever.

Nebulas across the universe are disappearing.

Is our galaxy running out of gas?

New research shows that across the universe,

the birthrate of stars is falling fast.

Researchers predict that 95% of all the stars

that will ever exist have already been born.

Sutter: In order for a galaxy to be healthy,

to keep making stars,

it needs to keep collecting new reservoirs of gas,

of raw material.

Bullock: Our galaxy is running out of gas,

and in fact, galaxies all across the universe

are slowly running out of gas.

That cycle is winding down, and someday it will stop.

More and more gas is locked up in low-mass stars

that never go supernova,

and the massive stars that do go out in a blast

push the gas away.

Sutter: Galaxies eject material.

Supernova winds and fountains are constantly sending streams

of gas and particles outside the galaxy.

But stars are not acting alone.

They're in cahoots with something even bigger.

Experts think the main culprit

lies at the center of every galaxy ...

a super-massive black hole.

In the past, even the milky way has experienced this gas loss.

Bullock: Just a few hundreds, millions years ago,

the central black hole was pretty massive,

and it gobbled up some material.

In this process, it released a lot of energy.

It sort of burped up a lot of energy.

It released gas, and some of that

probably escaped the galaxy altogether.

Right now our galaxy is still forming stars.

But the gas tank needs refilling.

Galaxies run on hydrogen.

It's what creates nebulas, it creates stars.

So, it looks now like we may have reached a bit

of a refueling stop.

In space, we've discovered a giant cloud of hydrogen

heading right for us.

This hydrogen cloud is massive.

10,000 light-years long by 3,000 wide.

Scientists call it Smith's cloud.

The thing is, it's orbiting our milky way,

and in about 27 million years,

it's going to slam into the disc of our galaxy.

The collision will re-energize the galaxy,

jump-starting star formation.

There's a lot of gas in there.

There's about a million times the mass of the sun.

You could make a million suns.

But this is only a snack.

To keep forming stars, the galaxy needs regular feeding.

Here in the milky way, we're still forming stars,

and that's because our galaxy is a cannibal.

It's surrounded by dwarf galaxies, and it's eating them,

and it's stealing their gas and their dust.

We're the product of mergers,

many small galaxies coming together and colliding.

When a new galaxy collides with the milky way,

it brings with it new gas, new dust,

the potential to form new nebulas.

So, by eating its own kind, the milky way is pulling out

a few billion more years of star formation.

But our galaxy

is always looking for its next meal,

and in a few billion years,

it will feast on its next-door neighbor,

the Andromeda galaxy.

When Andromeda merges with the milky way,

it's almost certainly going to deliver a fresh amount of gas.

Although this is a catastrophic train wreck

on a galactic scale,

it's actually kind of a good thing

because when it happens,

more stars will be born inside of the milky way.

That's going to extend the life of our galaxy,

if you want to think of it that way.

But there are only so many galaxies nearby

for the milky way to feed on.

Eventually, over the long run,

the nebular gas is being used up.

When that gas is gone, that's it.

You can't form any more stars.

And so, whatever happens at that point,

that will be the last generation of stars.

With no gas to replenish them,

nebulas will disappear across the universe.

The universe really is winding down.

Nebulas themselves are being depleted and dying away.

The last stars will eventually blink out.

From here on out, everything goes dark.

Nebulas ...

one of the most spectacular features

of the universe.

One of the things that make nebulas so appealing

is that they're just so beautiful.

But it's more than just beautiful.

They are cradles of creation.

Nebulas are quite literally the starting point

and the ending point of stars, and therefore planets and life.

I think it's incredible that we can learn about the cosmos,

and I think in the end, we're really learning about ourselves.

They are our connection

to the cosmic circle of life.

Nebulas are almost like an analogy for our own lives.

They're incredibly beautiful, but yet, they're transitory.

They're not going to be here forever.

And that's the story of our universe.

It's a story of change.

So, seize the day.