NARRATOR: In the beginning,
there was darkness, and then, bang, giving birth to
an endless, expanding existence of time, space, and matter. Every day, new discoveries
are unlocking the mysterious, the mind-blowing, the deadly
secrets of a place we call the universe. [music playing] 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 supernova 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. [music playing] 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 from previous explosions
of stars as supernovae. NARRATOR: The local fluff
is 30 light years long, about 180 trillion miles. It's inside a larger,
chimney-shaped gas cloud called 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. ALEX FILIPPENKO: 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 on, because 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. GPS: Turn left in 30 feet. [music playing] 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. ALEX FILIPPENKO:
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. LAURA DANLY: 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 was still sorting itself out. There are 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. ALEX FILIPPENKO: 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 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 don'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. LUCIAN WALKOWICZ: 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. LAURA DANLY: The galactic center
has a black hole 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 ultraviolet radiation. With these stars, you
don't worry about sunburn, but extinction. LAURA DANLY: 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. LUCIAN WALKOWICZ: 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 Rosetta 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 1,000 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? SEAN CARROLL: 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. 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 end 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. [music playing] 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 that keep the bad stuff away. Many cities on the
edges of rivers are oceans have dams and levees
to protect them from floods. If the dams and
levees fail, disaster. We've got threats and defenses
on a galactic scale too. LUCIAN WALKOWICZ: 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 disassociate 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. CLIFFORD JOHNSON: 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. [music playing] 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. 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 9 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
1 and Voyager 2, 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, but reform
into violent magnetic froth, and each bubble in that froth
is 100 million miles wide. SEAN CARROLL: We used
to think that it was a small, 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. [music playing] 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. Sort of like looking here
behind me is 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 a
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. CLIFFORD JOHNSON: 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 infrared vision,
similar to that used by commercial infrared cameras. I've brought with
me this plastic bag, and when I put my hand
the side 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
you're telescopes can see are actually invisible in
another part of the spectrum. You can see what's behind. NARRATOR: With infrared and a
multitude of other wavelengths at our command, we've
discovered a lot of neighbors we didn't know we had. CLIFFORD JOHNSON: 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. [music playing] 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. 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 going to 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
nonviolence, 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. LUCIAN WALKOWICZ: 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 delivers 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 extraterrestrial 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 a solar system, it becomes more and
more significant. When it's about a light
year away or less, than it becomes very important. NARRATOR: Almost exactly 1
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. [music playing] 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
where 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 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 comments toward the inner solar system. And all it takes is one
comment to hit Earth to cause a catastrophe. [music playing] 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. ALEX FILIPPENKO: 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 4. 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. [music playing] 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 was
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. [music playing] 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
Centaur, is an M-type star. It's a very low-mass star,
having perhaps only 12% the mass of our sun. It is 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. ALEX FILIPPENKO: 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. LUCIAN WALKOWICZ:
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. LUCIAN WALKOWICZ:
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 seek. NARRATOR: In 2011, one of
NASA's space telescopes, the Wide-Field Infrared
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. LUCIAN WALKOWICZ: 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 is 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. LAURA DANLY: 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. LUCIAN WALKOWICZ: 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. MICHAEL MISCHNA: 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 house. And ever since then, the
entire neighborhood has grown. You've 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. LUCIAN WALKOWICZ: 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. LUCIAN WALKOWICZ: 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 homeworld. It's actually a planet that's
icy and gas, 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. LAURA DANLY: 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. MICHAEL MISCHNA:
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 learn 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. ALEX FILIPPENKO: Now,
you might wonder, Pluto is not all that distant. Why did it take 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. LUCIAN WALKOWICZ: 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? [music playing] Our place in the Milky
Way has a lot of pluses. 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 wailing] 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. CLIFFORD JOHNSON: 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 the shockwave, that if you're
near enough to the shockwave, it would be destructive. If it's 10 light years away or
so, then high-energy radiation, like from x-rays and
gamma rays, can harm us. It 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
combined 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. [music playing] 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 supernova 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 HR 8210,
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. LUCIAN WALKOWICZ: HR 8210 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. ALEX FILIPPENKO: 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 Ia supernova. NARRATOR: Are we far enough
away to avoid being collateral damage when HR 8210 explodes? If you want to be completely
safe from a supernova, you should be at least
100 light years away. 10 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 HR 8210 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? [music playing] 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
going to 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 millions 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 going to be
an interesting place to see in a billion years. [music playing]
