All language subtitles for The Universe s07e03 Our Place In The Milky Way.eng

Narrator: In the beginning,
there was darkness,

and then, bang!

Giving birth to an endless
expanding existence of

time, space and matter.

Everyday, new discoveries
are unlocking the mysterious,

the mind-blowing, the deadly

secrets of a place we
call the universe.

In the universe, it's important
to know your nearest neighbors.

But how much do we really know
about our corner of the Milky Way?

In just the last few years,
scientists have uncovered

incredible secrets lurking
in our own backyard--

New moons, new planets,
and new mysteries.

It's like there was a house in
your neighborhood that you never

knew was there.

Narrator: Meet new neighbors
who are just passing through.

There are planets that
are wandering the galaxy

aimlessly without a
place to call home.

Narrator: And old friends
whose days are numbered.

It's conceivable that Betelgeuse
will go super nova tonight.

Narrator: Join us for a tour
of the neighborhood we're only

now getting to know.

This is "Our Place
In The Milky Way."

[Dramatic music]

Sync and corrections by n17t01
www.addic7ed.com

This isn't your neighborhood.

Neither is this.

Or this.

Or any of these.

And it isn't even this.

Looked at from a wider
perspective, your neighborhood

is a big cloud of gas.

Astronomers say the Solar
System is moving through "the

local interstellar cloud,"

also called "the local fluff,"

because of its low density
and irregular shape.

The gases are mainly
hydrogen and some helium.

There are trace amounts of
heavier atoms like carbon and

oxygen and nitrogen that are
just floating around the

interstellar medium.

We know that the heavier atoms
in the interstellar medium are

left over from previous explosions
of stars as supernovae.

the local bubble, also the
remnant of an ancient supernova.

The bubble is 300 light years
long, and lies in the inner edge

of one of the spiral
arms of the Milky Way.

And that's our neighborhood.

At least, we think it is.

Our exact position in
the Milky Way galaxy

relative to the arms
actually isn't known.

The structure of the galaxy is
not known in any real detail.

Some people think there are two
major arms, some people think

there are four major arms.

It's hard for us to determine
the exact structure

of our Milky Way, where all the
arms are and so onbecause

it's kind of like a mouse being
inside a maze; you don't get

the big picture.

Narrator: In almost any Earth
neighborhood, you can determine

your location very precisely.

Turn left in 30 feet.

Narrator: But when you're
dealing with something as big as

the Milky Way, GPS
isn't an option.

The galaxy is, you know,
100,000 light years across.

Narrator: Even exploring our
local neighborhood involves a

lot of uncertainty.

But if we did have a "Galactic
Positioning System," it would

probably locate us about midway
between the top and bottom of

the Milky Way, and about midway
between the galaxy's outer edge

and inner core.

Our Solar System is about
26,000 light years away

from the center of our galaxy.

Narrator: According to one
hypothesis, we have a very

exclusive location.

There is one idea that only
stars in a certain range of

distances from the center of our
galaxy are in the so-called

"galactic habitable zone," that
is, able to have life on planets

surrounding those stars.

It is just the right
place with a star of the

right temperature and a planet
at the right distance for there

to be a lot of liquid water on the
surface, where the chemistry

of life began and
evolved into us.

Narrator: The overall range
of the galactic habitable zone

extends from about 13,000 to
35,000 light years from the

center of the Milky Way.

The main part, where we are,
ranges from 20,000 to 29,000

light years from the core.

Inside the zone, old
neighborhoods have been

destroyed, to make a
place we can call home.

Depending upon how you
look at things, our local

neighborhood, our local Solar
System, is actually a

relatively safe place compared
to what seems to be going on if

you look at the
universe in the large.

In the early history of our
Solar System, it was a

much more violent place.

And the material that formed
the Sun and the planets

were still sorting itself out.

There were all sorts of
collisions and violent

things happening that gave
rise to this nice, calm, or

relatively calm, place
that we have today.

We think that the earliest
stars formed out of hydrogen and

helium alone; but that, over
time, the stars work as these

processors that create
the heavier elements.

This is important because
when those stars

eventually die and explode,
these supernovae or stellar

death explosions seed the
galaxy and the material around

it with heavier elements.

So for example, the carbon
in our cells, the oxygen

that we breathe, the calcium in
our bones, the iron in our red

blood cells-- All those
are heavy elements.

We know that the Sun is at
least a second or a third

generation star, because
there are planets around it.

There are things made of iron and
carbon and other heavier elements.

Narrator: But the processes
that led to life on Earth don't

seem to exist outside the zone.

Closer to the edge of the galaxy,
fewer massive stars have

exploded, producing
fewer heavy elements.

Further out in the galaxy,
you don't have as many atoms

like carbon, nitrogen, oxygen--
The atoms that are so important

for the chemistry of life.

So the habitable zone
of the galaxy cuts off

at a distance where you just
won't have the heavier atoms

to make life.

Narrator: If the outer galaxy
is a bad neighborhood, the inner

area is even worse.

Gravity from massive gas giant
planets could tear us apart.

And there are other dangers the
closer you get to the galactic core.

Back in the times of
Copernicus, we thought that we

were the center of our
universe; and even as we

started to learn more about the
heavens, eventually, we still

thought that we were the
center of the galaxy.

Now that we know even more,
though, it actually

turns out that we're lucky we're
not in the center of the galaxy.

Narrator: At the center of
the Milky Way, sucking matter

and even light into it, is
"Sagittarius A-star," a black

hole nearly 14 million miles
across with a mass 3.7 million

times that of our Sun.

If the galactic center has a
black hole in it, it gives off

a lot of radiation-- Enough to
fry life as we know it--

So you can't be too close to that.

Then there are other regions
in the galaxy that are also

probably not so great for life,
because there's just so much

radiation from nearby,
really hot O-type stars.

Narrator: O-type stars are
giants; they're hotter than the

Sun, 10 to 50 times as massive,
and throw out titanic amounts of

ultra-violet radiation.

With these stars, you don't worry
about sunburn, but extinction.

It's probably not
easy to survive in an

environment where you're in a
tight cluster with a lot of

O-type stars.

Narrator: O-type giants can
destroy planets before they form.

The radiation from these
stars is so strong that

it actually sweeps the material
away from these newly-forming

would-be planetary systems and
rips it out of the orbit of

their stars.

Narrator: If you want proof,
look at the Rosette nebula.

It's 5,200 light years away, far
outside the local bubble; but it

shows what O-type giants could
do to our neighborhood.

A 2008 study by the University
of Arizona of a thousand stars

in the nebula found star after
star had been made barren by

being too close to a blue giant.

So, what's a safe distance from
the radiation of an o-type giant?

Well, if you ask me, you can
never be too far away from a giant.

If you're life like us here on
Earth-- We're used to our fairly

tame Sun-- You want to be
probably at least tens of light

years away, maybe
more than that.

Really, just don't
get too close.

Narrator: Like a city between
a desert and an ocean, our

corner of the galaxy thrives
between two different

inhospitable regions.

With the elements of life and
without the threat of intense

radiation, it seems like our
neighborhood is literally the

only place to live.

But is our place in the Milky
Way really so exclusive?

The idea of the galactic
habitable zone is that if

you're too close to the center of
the galaxy, there's all these

crazy things going on, and
it tends to kill off life.

To be honest, I'm personally
skeptical of the idea, because I

think that life can happen in all
sorts of environments, or at

the very least, we don't know,
so we should be open-minded.

It's possible that our kind
of life can only live

in this galactic habitable zone,
but elsewhere there could

be other kinds of life that
we would call extremophiles.

On the other hand, they would
call us extremophiles.

Narrator: One thing is
certain-- In our neighborhood, we

have a sun that, unlike a blue
giant, protects us from danger

and destruction, in ways that
we're still learning about.

That protection may be
invisible, but if we lose the

Sun's protection, our
neighborhood could be doomed.

Narrator: Our place in the
Milky Way seems pretty peaceful

because, like a lot of
communities, we don't give much

thought to the 24/7 security systems
at keep the bad stuff away.

Many cities on the edges of
rivers or oceans have dams and

levies to protect
them from floods.

If the dams and levies
fail-- Disaster.

We've got threats and defenses
on a galactic scale too.

Space is filled with
radiation known as cosmic rays.

Cosmic rays are bad for
us in the same sense

that nuclear radiation here on
Earth would be bad for us...

Because high energy radiation
tends to dissociate carbon

bonds, which is
what we're made of.

What you're really doing is
damaging your DNA, and there's a

potential there that you could
start to have mutations based

off of that.

Narrator: Some mutations can
help a species survive or lead

to extinction.

There's no evidence
that cosmic radiation has

really negatively impacted
Earth in the past, but it's

nothing that you want
to play around with.

Narrator: Our neighborhood's prime
defense against cosmic rays-- Magnetism.

We have this zone of
protection in our neighborhood.

Of course the Earth
has a magnetic field,

due to how things move around
in the core of the Earth.

The Sun also has a powerful
magnetic field and it also has

the solar wind.

These phenomena actually
generate ways of protecting us

from things that come from
outside the Solar System.

Narrator: The Sun's magnetic
field is twisted by the solar

wind, streams of charged protons
and electrons that shoot

out of the Sun at a
million miles an hour.

And then the particles
that live in the Solar

System between the planets
actually stretch the lines of

the magnetic field around
in complicated patterns.

Narrator: The solar wind
carries the magnetic field more

than three times farther out
than the orbit of Neptune.

But nine billion miles away, at
a place called the heliopause,

the solar wind runs out of steam,
and slows to almost nothing.

As it slows, it twists the
sun's magnetic field into a

barrier against cosmic rays
from interstellar space.

This is the heliosheath.

If it wasn't for the
heliosheath, these cosmic rays

would actually pour into our
Solar System all the time.

The heliosheath acts as a
kind of shark cage for these

incoming cosmic rays that might
otherwise influence our planet.

Some do come through, but
they don't come through as

strongly as they would
without that protection.

Narrator: It used to be thought
that the heliosheath was

a rather elegant barrier, made
of flowing curtains of magnetic

force, but recently, enter Voyager
I and Voyager ii,

probes sent out from
Earth in 1977.

In the early 21st century,
these disco-era devices

sent back information
indicating that the Sun's

magnetic field lines don't flow

smoothly together; they break

up and reform into violent

magnetic froth, and each bubble

in that froth is 100
million miles wide.

We used to think that it
was a smooth, nice barrier

between them, but in fact, it's

a roiling place with all sorts
of bubbles and patterns.

I think there's always been
people who think the

universe is more elegant than

it is and people who think it's

more violent than it is, and

we're always surprised
one way or the other.

The truth is that some aspects

of the universe are quite

elegant, and in other aspects,
it's quite a mess.

Narrator: Where are the

elegant areas of our galactic

neighborhood and where
are the rough parts?

It can be hard to tell
with all that gas and

dust in the cosmos.

It's sort of like looking

here behind me at Hollywood;

there's even a landmark there,

the Capitol Records building.

You can barely make it out.

And even beyond that, there are

some hills that are even hazier.

It's because there's stuff in

the air that blocks the view.

The hill itself obscures my

ability to look beyond it, and

that's kind of like the dust in

very dense molecular clouds.

When you hit a big wall of the

dense molecular cloud filled
with dust, you can't see

anything.

Narrator: When
we explore our

galactic neighborhood, what we

see depends on how
we look at things.

One of the things we've
learned through the

history of looking at the sky

is that every time you look in

a different way, you see new
things, and looking at the

sky a different way often
simply means looking in a

different part of the
electromagnetic spectrum.

As we look up into the sky
with our eyes or with the

aid of optical telescopes,
in the visible part of the

spectrum, we see the night sky,

and there's a lot to see, but

it's only a fraction
of what's out there.

Narrator: Some space
telescopes see through cosmic

dust with infra-red vision,
similar to that used by

commercial infra-red cameras.

I've brought with me this
plastic bag, and when I

put my hand inside of the bag,

you can't see how many
fingers I'm holding up.

With the infrared camera, you

can see the heat coming off my

body, so my face, which is

warm, is red and white, but my

hair, which is cool,
shows up as blue.

So with the infrared camera,
you should be able to

make out how many fingers I'm

holding up, even though you
can't see through this bag.

That's how astronomers peer

through cosmic dust when they

want to see things that
are hidden from sight.

For example, stars being
born are very warm,

but they're obscured by dust

shells; with infrared,
we can see them.

Certain objects are transparent
or opaque depending

upon the frequency of the light

that's trying to
get through them.

And so, in fact, something

that's getting in the way, like

a lot of interstellar dust or

gas, is getting in the way of

what your telescopes can see,
are actually invisible in

another part of the spectrum.

You can see what's behind.

Narrator: With
infra-red and

a multitude of other
wavelengths

at our command,
we've discovered

a lot of neighbors we
didn't know we had.

There's a whole array
of instrumentation

which is exploiting that
lesson that if you look in a

particular part of
the spectrum,

you see the sky in a
very particular way.

Narrator: From what we've

observed, it looks
like some old

neighbors might
have helped life

form on Earth while some newer

neighbors may be planning
to wipe us out.

Narrator: As we've explored
our place in the Milky Way,

we've met a lot of interesting
new neighbors, but there are

good neighbors and bad ones.

[Dog barking]

Good neighbors are, for
example, objects that are in

predictable orbits, moving
around, doing their own thing,

minding their own business.

We can look over and wave to
them, but they're not gonna

do something sudden
or dangerous to us.

The bad neighbors, then,
would be things that may do

something unstable.

They may do something that could
affect us in a way that we can't

predict when it's
going to happen.

So that might be when a star
dies and explodes, or it

might be when something collides
and bounces off something else

and comes spinning
in our direction.

So, classifying things roughly
into good neighbors and

bad neighbors is really a
classification into predictability and

unpredictability, or violence
and non-violence if you like.

Narrator: Sometimes, a good
neighbor will bring a "moving

in" gift.

That might have happened to
us, billions of years ago,

as the Earth was still
cooling and forming out of

recycled material
from a recycled sun.

We might have received a gift
that changed everything.

The early Earth was
very hot and probably any

original surface water
evaporated away, so we think

that quite a bit of the water may
have come from either comets

or icy asteroids or both.

One of the theories about how
we might have gotten so much

water here on Earth is from icy
bodies in the outer Solar

System, left over from the
formation of the Sun and the

planets, crashing into our inner
Solar System where Earth

lives and deliver
some of that water.

Narrator: According to one
recent theory, about four

billion years ago, the gravity
of gas giants like Jupiter sent

icy asteroids slamming into Mars,
Earth and Venus, but only

on Earth did the ice
penetrate into the mantle.

The water softened the Earth and
initiated a titanic process of

plate tectonics, which led to the
emergence of continents and oceans.

And what of the life that
formed in the oceans?

Did organic compounds necessary for
life also splash down from space?

In rare meteorites called
"carbonaceous chondrites,"

scientists have found organic
compounds like those that

helped form life on Earth.

These compounds are similar to
what's been collected from many

different sources, including
antarctic micro-meteorites,

interstellar dust, and comet
samples acquired by NASA's

"Stardust" mission in 2005.

The origin of life involves a
long series of reactions with

many different organic
molecules, organic molecules

being just ones with carbon in
them, and it's possible that

different circumstances are
needed to make the different

organic molecules.

Some of them might be made here
on Earth, but others might be

easier to make out in space and
then bring them here to Earth on

asteroids or comets.

Narrator: It's possible that
without extra-terrestrial gifts

from our neighbors in space, life
on Earth might never have happened.

Milky Way neighbors may have
helped nurture us, but the

Milky Way has things that can
kill us as well, with something

like this-- An orange
dwarf named Gliese 710.

It's about 60% as massive as the
Sun and is currently just 63

light years from Earth
and getting closer.

Gliese 710 appears to be
heading pretty much straight

toward the Solar System.

As an orange dwarf approaches
the Solar System, it becomes

more and more significant.

When it's about a light year
away or less, then it becomes

very important.

Narrator: Almost exactly one
light year away from Earth is a

huge region of icy objects
called the Oort Cloud.

The Oort Cloud objects could
turn into comets if they were to

come close enough to the Sun, but
usually we don't see them at

all because they're so
far away from the Sun.

Narrator: Billions of potential
comets are waiting for

something to give them a
gravitational push-- Something

like Gliese 710.

It'll start intersecting
the Oort Cloud or at least

gravitationally disturbing it in
something like 1.3 million years.

Narrator: If Gliese 710 gets
close enough, its gravity

could turn harmless chunks of
ice and dust into rampaging

comets launched at us.

The results for Earth
could be devastating.

At that point, there
could be a huge onslaught

of comets into the inner Solar
System that could lead to

another mass extinction.

We don't know that that'll
happen, but it could happen.

Narrator: Astronomers say
there's an 86% chance that

Gliese 710 will barrel right
through the Oort Cloud.

So if the orange ball was like
an orange dwarf like Gliese 710

and the pins were the Oort
Cloud, this is one thing

that could happen.

All right, but here's something
else that could happen.

There's a 14% chance that Gliese
710 is just gonna pass right by,

outside the Oort Cloud, not
coming inside it at all.

Narrator: But even without a
direct hit, the effect of the

star's gravity could disrupt at
least some comets and send them

straight for us.

So the star could knock
just a few comets toward the

inner Solar System.

And it takes is one comet to
hit Earth to cause a catastrophe.

Narrator: We've got more than
just Gliese 710 to worry about.

There are more than 150 stars
close enough to disturb us

within the next two
million years.

The stars in our Milky
Way galaxy are all

gravitationally bound together,
so they're moving in various

directions, overall a rotation
around the center of our

galaxy, but not all the
orbits are exactly the same.

That means, from our perspective,
a given star might

be going away from
us or toward us.

Narrator: And NASA estimates
there are more than 20,000

near-Earth asteroids more than 300
feet across, like 2005 YU55,

which, in November 2011, came
closer to the Earth than the Moon.

It might come even
closer in 200 years.

How bad would it be to get
hit by a rock like that?

Think about Nagasaki at the end of
World War II and multiply by four.

As we've searched our corner
of the Milky Way for other

neighbors, bad and good, we've
found some very unexpected things.

We now have evidence of
stars cold enough to touch

and planets straight out
of science fiction.

Narrator: Exploring our place
in the Milky Way has turned up

one surprise after another.

It's like there was a house
in your neighborhood that you

never knew was there and that
you've suddenly discovered, but

it's just down the block.

Narrator: Take Alpha Centauri,
the brightest star in

the constellation Centaurus and,
after the Sun, our nearest

neighbor star, 4.3 light years,
or 25 trillion miles, away.

In the 17th century,
astronomers announced that

Alpha Centauri was
really two stars.

Then, in the 20th century, it
turned out to be a triple system.

Alpha Centauri "A" is very
much a Sun-like star, nearly

exactly the same
mass as our Sun.

Alpha Centauri "B" is a
little bit less massive.

The third star, Proxima
Centauri, is an M-type star.

It's a very low-mass star,
having perhaps only 12% the

mass of our Sun.

It's so faint that we can't
see it with our unaided eye.

Narrator: It turns out that
other very well known neighbor

stars are also multiple systems.

Sirius, just 8.6 light years
away and famed for thousands of

years as the brightest single
star in the sky, is really a

binary star.

Most stars are less massive
and smaller than our

Sun and most stars are
in binary systems.

In both respects, our Sun is a
little bit of an exception.

The majority of stars are
red dwarfs or brown dwarfs.

Red dwarfs make up 70% of
the stars not only in

our galaxy but in the universe,
and so even though we

orbit our Sun and we tend to
think of it as the iconic star,

really, the red dwarfs
are far more common.

Narrator: As for the brown
dwarfs, these are neighbors we

weren't sure existed
until the 1990s.

They're not quite stars,
but they're not planets.

Oh, and they're not
really brown, either.

The brown dwarfs are some
of the most mysterious

denizens of the solar
neighborhood because they're

really very, very cold and
they're very dark, and that

means that they don't give off a
lot of light and they're very

difficult to see.

Narrator: In 2011, one of
NASA's space telescopes, the

wide-field infra-red survey
explorer, or wise, found a

series of brown dwarfs right in
our neighborhood, between 9

and 40 light years away, with
surface temperatures once

considered impossible.

One of these brown dwarfs
that we found is actually so

cool that you could touch
it with your hand.

It's only 80 degrees
fahrenheit, the same

temperature as a really
lovely day out here on Earth.

And so, who knows
what else we'll find.

The more we look,
the more we see.

Narrator: Why are stars
so many different colors?

That's what Anna K. of
Baton Rouge, Louisiana, texted to ask

The Universe.

Anna, that's a really
interesting question.

Basically, stars have slightly
different colors because they

have different surface
temperatures.

Cool stars like Betelgeuse
look reddish and they have

temperatures of only 6,000
or 7,000 degrees fahrenheit.

The hottest stars, like Rigel,
appear bluish, and they're

upwards of 20,000 degrees.

Then there are stars like the
Sun, with temperatures of

10,000 or 11,000 degrees,
and they look white.

Now, the Sun looks yellow when it's
setting, but that's because

of atmospheric effects.

Its true color is white.

Narrator: There are
more than stars out there.

We've discovered hundreds of
neighboring planets inside and

outside the local bubble.

We have discovered a lot of
exoplanet candidates through a

mission called Kepler that is
looking at essentially little

eclipses, when a planet moves
in front of its parent star and

then out, and the light dips a
little and then goes back up.

It's very difficult to see,
analogous to watching for a

single light bulb going out on
the Vegas strip, but Kepler is

capable of doing these
measurements so precisely that

it's able to find even planets as
small as our own Earth around

stars like our Sun.

The first exoplanet we
discovered was only about

15 years ago, and it was very
much like we were the only

house on the block and we saw
the first neighbor putting up

their hosee, and ever since then,
the entire neighborhood

has grown, you built up
communities of other exoplanets

out in our local neighborhood.

Narrator: As far as we know,
our nearest planetary neighbor

outside the Solar System is just
down the street, 10.5 light

years away, orbiting the
orange star Epsilon Eridani.

This planet isn't exactly
something that we could go

visit and expect to find life.

We think that this planet
is more equivalent to a

planet like Jupiter in our
Solar System-- A big ball of

gas which, as we understand
it anyway, isn't a great

place to look for life.

Narrator: A little farther
out, about 200 light years, is

another surprise-- A planet that
looks like something out of a

Star Wars movie.

Just recently, the Kepler
telescope discovered a

planet that orbits two suns, and
this is a planet called Kepler 16B.

So, this planet, even though it
has similarities to Tatooine,

isn't exactly like Luke
Skywalker's home world.

It's actually a planet that's icy
and gassy, more like Saturn

than our own Earth.

Now we were never sure, prior
to this discovery, whether you

could have a planet that
actually has two suns, and so

now that we've found one, we
know that these are possible,

and that's really interesting,
because it means that these

binary systems are good
places to look for planets.

Narrator: In 2011, astronomers
unveiled a new kind

of planet in our
neighborhood-- The homeless.

There have been some
indications that there are

planets to be found that are not
in orbit around their parent star.

They started out in orbit
around their parent

star, but somehow got ejected
from their solar system and now

they're wandering the galaxy
aimlessly, without a place to

call home, so one wonders if
pretty soon we'll have another

new definition that encompasses
those bodies that used to be

planets and no longer
have a parent star.

I think it's still valid to
refer to these ejected bodies as

planets, because "planet" is the
Greek word for "wanderer," and

they are certainly wandering
through deep space.

Narrator: We've even learned
new things about our Solar

System neighbors.

In the summer of 2011, the
Hubble space telescope

took the first pictures
of the dwarf planet

Pluto's previously
unsuspected fourth moon.

Now you might wonder, Pluto
is not all that distant.

Why did it take us so long
to find a fourth moon?

Well, it's because it's very,
very small, only 10 to 20 miles

in diameter, so it's very faint.

It reflects only a little
bit of the Sun's light.

Narrator: The new moon is
probably a frozen, lifeless

world like Pluto itself.

So far, all of our
newly-discovered neighbors have

been too hot or too cold to have any
possibility of our kind of life.

But the search goes on.

So even though we haven't
done it yet, we're at

this point where our technology
has caught up to our needs and

we're actually going to be able
to start finding those planets

like Earth in the
really near future.

However, being able to
determine whether they

would be supportive of life is
a much more difficult task.

Narrator: None of the
exoplanets we've discovered in

our corner of the Milky Way pose
any threat to us, but what about

some of the stars out there?

Could some of them die
and take us with them?

Narrator: Our place in the
Milky Way has a lot of plusses.

We're right in the zone for
life to form, our closest star

protects us from dangerous
cosmic rays, and most of our

neighbors don't disturb us.

But neighborhoods can change.

[Siren]

If a fire destroys a nearby
home or business, your home

could also be damaged, so
imagine what might happen

when a star goes out of
business as a supernova.

That means they'll explode
and throw all their innards

back out to the galaxy.

Narrator: Exploding stars
created us, most of the heavy

elements in the stars around us,
and the gas clouds the solar

system dwells in, but it's a bad
idea to be too close when a

dying star explodes.

A supernova explosion is an
incredibly powerful explosion.

The core of the star
bounces out and smashes

into the outer layers and blows
them out into the galaxy.

So what actually happens is that
material gets thrown out in

a shock wave that if you're near
enough to the shock wave would

be destructive.

If it's ten light years
away or so, then high energy

radiation like from X-rays
and gamma rays can harm us.

They can, for example, destroy
part of the ozone layer.

What happens is, the radiation comes
in, disrupts nitrogen molecules.

The nitrogen atoms then combine
with oxygen to form nitric oxide.

That nitric oxide, NO,
disrupts ozone molecules O3,

and forms nitrogen dioxide, NO2.

The nitrogen dioxide can then
combine with atomic oxygen,

forming more nitric oxide, which
then disrupts more ozone,

which leads to a
snowball effect.

So, within a few weeks, you
can destroy much of the

ozone layer, allowing the Sun's
ultraviolet radiation to come

in, and that would then kill
life that's on the surface

layers of an ocean or in ponds.

Narrator: That death toll
would include the phytoplankton

that are the foundation of the
marine food chain and provide

50% of the Earth's oxygen, and
that would spell doom for most

larger forms of
life, including us.

One candidate for stellar
extinction lies outside the

local bubble, although it's
been a familiar sight for

thousands of years-- The red
supergiant Betelgeuse.

The star, between 500 and 800
light years away and 20 times

the mass of the Sun, forms
the right shoulder of the

constellation Orion.

Betelgeuse is getting
near the end of its life.

Narrator: Between 1996 and
2011, Betelgeuse shrank by 15%

for reasons that are
still not understood.

The red giant may go
supernova in half a million

years, or it may have
already happened.

It's conceivable that
Betelgeuse will go super

nova tonight or tomorrow night or
next week, but it's much more

likely to become a supernova
in 100,000 years or

in a few 100,000 years.

Given that Betelgeuse is at least
a few hundred light years

away, it's possible that it's
already blown up and we just

don't know it because the
light hasn't reached us yet.

Narrator: The good news
is that, even if Orion does

dislocate its shoulder,
Betelgeuse is too far away to

harm our neighborhood.

But then there's HR8210, about
150 light years away, in the

constellation Pegasus.

It's not one star but two-- A star
and a white dwarf in binary

orbit around each other.

The white dwarf is about 15%

more massive than our Sun-- Not at
the supernova tipping point yet.

HR8210 is this binary
system, two stars that are

orbiting one another, one
of which has actually

already died and
is a white dwarf.

Now, this system has the
potential that when the star

that's very hot right now starts
to go through its death throes

and starts to puff up as it dies,
it might start to pour material

onto that white dwarf.

Essentially these systems are
like zombie stars eating

their companions.

When that normal star starts to
expand, the white dwarf will start

stealing material from its
companion, becoming more

massive, and if it reaches a
certain unstable limit, it'll

blow up as a type 1A supernova.

Narrator: Are we far enough
away to avoid being collateral

damage when HR8210 explodes?

If you want to be
completely safe from a

supernova, you should be at least
a hundred light years away.

Ten light years might be
enough, but it might not;

it depends on what effect
kills you first.

But that won't happen
for a really long time,

and by then we will have
moved off and it will have

moved off because everything in
the galaxy is really on its way

somewhere.

So over time that might
happen, but at the point

that it does, it probably won't
be very close to Earth at all

anymore.

Narrator: But don't
feel too comfortable.

The threat of HR8210 was
only discovered in 2002.

How many more potential
supernovas are out there?

How close are they to us?

And how soon will they explode?

To possibly make matters worse,
some astronomers say that there

are a lot more supernovas in
our neighborhood's future.

Our Solar System
orbits our galaxy at a

different rate than
the spiral arms do.

That means, eventually we're
gonna enter a spiral arm,

and because there is a lot more
massive stars there, some of

them will be ending their lives,
creating supernovae and

posing a greater threat
to life on Earth.

Narrator: Still, our place
in the Milky Way is secure for

tonight and for at least a
few million nights to come--

Plenty of time for more
exploration and more surprises.

We live in a pretty diverse
neighborhood, actually, and

things are changing.

The galaxy is not a static
place, so it's gonna be an

interesting place to see
in a billion years.

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