[music playing] 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. In the "Star Wars"
universe, the Death Star is the ultimate weapon of mass
destruction able to annihilate entire planets. In the actual universe, the sky
is filled with real-life death stars They can be thought of
as sort of a time bomb. NARRATOR: Some are dangerously
close to our planet. ALEX FILIPPENKO: Earth's
life might take a bad hit when that radiation reaches us. NARRATOR: And one has the
Earth in its crosshairs. PETER TUTHILL: It
was almost a shock. I didn't believe it
when I first saw it. NARRATOR: They are
the death stars. And they make the universe
a very dangerous place. [music playing] Thousands of light years from
the Earth, a super massive star is preparing to hit the
self-destruct button. Stars explode every
day in the universe. But this one is different. It lurks in the
constellation Sagittarius-- the mythological archer
of the celestial zodiac. The star is called WR 104. And its destructive force could
be targeting us and taking aim at our fragile blue planet
with enough deadly radiation to ignite our
protective ozone layer. This would incite
drastic climate change, cause the extinction of many
plant and animal species, and potentially the
demise of mankind. WR 104 is just one of
millions of massive death stars in the universe. These savage celestial
bodies are aging giants preparing to blast themselves
into a stellar afterlife. At that point, the
outer layers of the star have nothing left to support
them against gravity. So they suddenly fall inwards. NARRATOR: Their last breath can
ignite the biggest explosion in the known universe-- a gamma ray burst, a blast far
exceeding the energy output of our own sun over its
entire 10 billion year life. If one were to target
the Earth, life as we know it could cease to exist. This is what could
happen with WR 104, making it a real
life death star. In the film "Star
Wars," the Death Star is the dark side's
ultimate weapon. The predatory star is
pure science fiction. But the reality is much scarier. ALEX FILIPPENKO: A
death star in real life is a star that blows up and
blasts any nearby planets with deadly radiation. You know, that's
a real death star. NARRATOR: WR 104 is what's
known as a Wolf-Rayet star. They are the largest
stars in the universe-- hulking beasts 30 times bigger
than our own sun, each of them counting down to Armageddon. Discovered by French astronomers
Charles Wolf and Georges Rayet in 1867, Wolf-Rayet
stars are the outlaws of the universe. Stars live by the credo
live fast, die young, leave a good-looking corpse. And the bigger they are,
the faster they live. And the faster the live,
the more violent their end. AMY MAINZER: They burn
through their nuclear fuel extremely quickly and exhaust
everything that they have. And so consequently, they
don't live very long, maybe a few tens of millions
of years at most. PETER TUTHILL: And they're
easy to find because they're the real T Rex's of
the stellar kingdom. They're immensely powerful. NARRATOR: In the year 2000,
Australian astronomer Peter Tuthill began studying
Wolf-Rayet 104 some 8,000 light
years from Earth. This giant was ominously
different from the others. Tuthill's team immediately
noticed an immense dust cloud around it 20 times larger
than our entire solar system. PETER TUTHILL: We knew there
was dust around Wolf-Rayet 104. And that was a puzzle because
it's a bit like finding a snowflake in hell. There was a mystery there. And we wanted to try
and solve that mystery. NARRATOR: Over the
course of six years, Tuthill used an infrared
camera at the Keck observatory in Hawaii to create a composite
image from multiple exposures. It yielded an amazing
time lapse sequence. 104 was producing an exotic
spiraling plume of dust. It was almost a shock. I didn't believe it
when I first saw it. I thought stars don't
look like spirals. There's no spiral I've
ever seen in a book. We then had a mad scramble. We had to try and understand
how a star can produce this elegant tail. NARRATOR: Tuthill
discovered that the key to the strange dust spiral was
the fact that WR 104 wasn't alone. It's locked in orbit with
a smaller star in what's known as a binary system. Both stars eject masses
of charged particles called stellar winds. These winds aren't
uncommon in the universe. Our own sun creates a
solar wind that extends beyond the outer planets. The difference is that
in a binary system, when winds from the two stars
collide, gases are compressed. And dust and soot are created. But what causes
this dust to form into such an exotic spiral? So it turns out that a lawn
sprinkler makes a great analogy to illustrate the
physics that's occurring in these colliding
wind binary systems. We've modified this sprinkler so
that it only shoots one jet out of the spigot. NARRATOR: The single water jet
represents the constant flow of dust particles being created
by the colliding stellar winds. But because the two
stars in WR 104's system are in constant orbit
around each other, it adds a circular motion
to the stream of dust. PETER TUTHILL: Your
first intuition is that the water is moving
in a circular motion. But in actual fact,
the lawn sprinkler is really shooting a
jet in a straight line. The water droplets even in
moving in a straight line away from the spigot,
they create an arc. And that arc wrapped into
a spiral with the rotation. NARRATOR: The spiral
spawned even more questions. The most troubling? Exactly what kind of death
star could WR 104 become? AMY MAINZER: Wolf-Rayet stars
can be thought of as sort of a time bomb because they're
so massive that they can't live for very long. And once they've burned up
all of their nuclear fuel, there's nothing left
to support the star against the relentless
pull of gravity. And at that point, the
core of the star collapses. And the outer layers
fall in on top of it and bounce outward in
a tremendous explosion. NARRATOR: The explosion
is a supernova-- an immense burst of
radiation that briefly outshines an entire galaxy. Wolf-Rayet 104 will definitely
go supernova sometime in the next few 100,000 years. At 8,000 light years
away, the explosion itself poses no threat to the Earth. But there's a chance the
supernova will trigger the most violent event in the universe-- a gamma ray burst. In a small percentage of
these massive death stars, a gamma ray burst is triggered
by the crushing transformation of a dying star
into a black hole. LISA KEWLEY: As
a star collapses, it produces a massive
electric field. And in an instant, the energy
from this electric field is turned into matter and
antimatter particles which then collide with each other and
produce a huge pulse of energy. NARRATOR: They are the
most powerful energy beams in the electromagnetic spectrum
more lethal than microwaves, infrared energy,
and even x-rays. Humans have learned to
harness deadly gamma rays for useful purposes,
such as food irradiation. By using gamma rays,
food processors can eliminate microorganisms,
bacteria, viruses, and insects. But the amount of
gamma radiation applied is an extremely tiny fraction
of the energy released in a stellar gamma ray burst. LISA KEWLEY: Gamma ray bursts
produce so much radiation that if we were to create
a gamma ray burst on Earth, it would be like a huge number
of nuclear bombs going off. It would be devastating
for life on Earth. [explosion] NARRATOR: For the human
race, the most critical piece of information about
gamma ray bursts is the direction of fire. At the moment of
collapse, the star becomes a dense, flattened disc. And the rotational axis poles
are its only openings free of dense star matter. You get two relatively
evacuated regions along the poles. And it's along those
directions that material can be ejected because
it encounters relatively little resistance. So this container of yogurt
provides a nice analogy for what happens in
a gamma ray burst. I'm going to drop the
container of yogurt. And because of the
sides of the container, yogurt is not going
to be able to go out along those directions. But the top of the
container is open. So yogurt is going to
squirt out along the top. Watch what happens. So the yogurt went squirting
basically straight up. It couldn't go out
the sides because it was blocked by the sides
of the yogurt container. And that's a nice analogy for
what happens in a gamma ray burst. NARRATOR: The greatest
concern for humans is the direction that the
gamma ray burst is firing. If the axis of the
collapsing star is pointing in our direction,
we could be in serious trouble. When Peter Tuthill's team
studied the plane of orbit of WR 104's dust plume, they
came to a shocking realization. PETER TUTHILL: This spiral
was the key that unlocked a lot of these secrets. And where things start
to get a little scary is that this system
at first blush appears to be almost face on. We're looking right down
the axis at the heart. It's like looking at a
plate, a dinner plate. If you take that plane, and you
tilt it to the line of sight, it looks inclined. You're no longer looking
at a circular dinner plate. NARRATOR: Further examination
suggests the rotational axis of the dust plume appears
to match the rotational axis of the Wolf-Rayet
star itself, meaning the Earth is staring directly
down the barrel of a gun. ALEX FILIPPENKO: That means that
if this star becomes a gamma ray burst when it blows
up, one of the two jets will be pointing toward us. NARRATOR: The beautiful
spiral of Wolf-Rayet 104 is suddenly a messenger of doom. Some 8,000 light years
from Earth, two stars are locked in a gravitational
dance, their stellar winds ejecting a vast cloud of
dust in a graceful spiral. But there's more
to this star couple than just a beautiful tail. The larger of the
two, Wolf-Rayet 104, is a massive death
star on the verge of exploding as a supernova. That much is certain. The real mystery is will it
also unleash a Gamma Ray Burst or GRB-- the most powerful burst
of energy in the universe? The question is an important
one for all on Earth, especially considering the
star's axis may be pointing directly at us. ALEX FILIPPENKO: That means that
when it blows up, if it becomes a gamma ray burst, the jet could
be pointing straight at us. NARRATOR: WR 104 is
counting down to destruction in the constellation
Sagittarius. Named by a Roman astrologers
over 2,000 years ago, Sagittarius is Latin
for the Archer. PETER TUTHILL: And you have
to ask maybe were the ancients onto something. Is there something to do
with the Archer aiming at us? ALEX FILIPPENKO: WR 104 can be
thought of as an arrow pointing our way if indeed it blows
up as a gamma ray burst. NARRATOR: There is little
dispute among today's astronomers that a tightly
focused beam from a gamma ray burst will travel vast
distances in space. In fact, on April 3, 2009,
the Swift multiwavelength observatory orbiting
the Earth recorded a GRB that occurred 13 billion
light years away from Earth near the very edge of
the visible universe. The blast occurred only
about 630 million years after the Big Bang. This means that gamma rays
from the exploding star traveled at the speed of
light for 13 billion years before they were visible to
us, making this gamma ray burst the oldest stellar object
in the known universe. ALEX FILIPPENKO: We know of no
star or galaxy that's farther away than this gamma ray burst. It's the single most distant
discrete object ever seen. NARRATOR: At only
8,000 light years, a GRB blast from Wolf-Rayet
104 could be catastrophic. ALEX FILIPPENKO: The flash that
we would see if Wolf-Rayet 104 went off would be much
brighter than the sun, especially at
gamma ray energies. A single gamma ray
burst can easily exceed the total light output
of millions of galaxies. And each of those galaxies
contains 100 billion stars. NARRATOR: This death star
is a ticking time bomb. Scientists know for sure
it will go supernova. But questions remain
about its potential to unleash a gamma ray burst
in the direction of Earth. PETER TUTHILL: That's the first
point we need to establish. If it does produce
gamma ray bursts, is that gamma ray burst
pointing towards us? NARRATOR: The spiraling
axis of the star appears to be aimed in
the direction of Earth. But with thousands of
light years to travel, would the GRB beam
actually hit the target? Would the Archer's aim be true? ALEX FILIPPENKO: We know it's
pointing roughly toward us. But it could be pointing
sufficiently away that the beam of radiation from the gamma ray
burst if it turns into a gamma ray burst will actually miss us. NARRATOR: However, if
the star is aligned, one powerful burst of energy
could turn the Earth's ozone layer into a
radioactive inferno. ALEX FILIPPENKO: Even
a gamma ray burst that's thousands
of light years away could deplete the ozone
layer to roughly half of its current level. Now, that won't kill
all of the species. But it could lead to what we
call a mass extinction where a good fraction of all living
species die rather suddenly. NARRATOR: So the
burning question is, will the death of WR 104
really trigger a gamma ray burst? Scientists just don't know. The mandatory requirement for a
star to produce a lethal gamma ray burst is high
horsepower rotation. All stars rotate on their axes. Some massive stars
can spin very fast. LISA KEWLEY: So
the rotating star, the rotational energy is part
of what produces the gamma ray burst. PETER TUTHILL: If you
can put the brakes on, if you can take that
rapidly spinning star and slow it down before
it gets to that stage, you've defused that bomb. NARRATOR: Based on mounting
scientific evidence, it appears the universe
itself is applying another set of brakes to its stars. It's called metallicity. Stars are primarily made
of hydrogen and helium. But heavier, more
complex elements are created every
time a star explodes, elements like carbon, nitrogen,
and oxygen that then become the raw materials for the
next generation of stars. So a star born today has
more heavy elements, also known as a higher metallicity,
than a star born earlier in the history of the universe. When a massive star has a
lot of heavy elements in it, it tends to lose a lot of
its mass through winds. And if it loses a
lot of its mass, it also loses a lot
of its rotation. And it ends up rotating
too slowly to form a GRB. PETER TUTHILL: So
something is happening to the Wolf-Rayet stars
today that's going up there and defusing all the bombs. So they're still blowing
up as supernovae. But far, far few of them
are taking that supernova to the next step as
a gamma ray burst. NARRATOR: Could these brakes
slow WR 104 enough to render it harmless to the Earth? Many astronomers believe so. But what if they're wrong? At 8,000 light
years away, is Earth really in the danger zone? [music playing] When the death star called
WR 104 finally explodes, it has the potential to
unleash a deadly gamma ray burst directly at Earth. It's believed the star is
roughly 8,000 light years away from us is this close
enough for a gamma ray burst to do
damage to our planet? Being 5,000 to 8,000
light years away, it's in the danger zone. Earth's life might
take a bad hit when that radiation reaches us. If it was another two or
three times further away, we'd probably be OK. And if it was two or
three times closer, we'd really be
shaking in our boots. But it's just at the edge of its
range where one would expect, well, you know, it
might do something. But it's probably not going
to roast us all in our sleep. So perhaps once
every billion years or so, there's a
gamma ray burst that's sufficiently close
and sufficiently well pointing toward us
that we need to worry. NARRATOR: Death stars of all
sizes populate the universe. But stars are not
the only entities capable of such violence. The universe is also home
to death galaxies like 3C321 also known as the
Death Star galaxy. ALEX FILIPPENKO: 3C321 is a
galaxy with a giant black hole in the middle millions of
times the mass of our sun. NARRATOR: Just outside
the black hole's edge, the chaotic churning of magnetic
fields and gravitational pull has ignited a high
energy particle jet. These jets are not uncommon. But this one is
delivering a beating to its nearest neighbor. ALEX FILIPPENKO:
The case of 3C321 is very interesting
because there happens to be another galaxy
20,000 light years away. The stars in that
galaxy are being blasted by the energetic
particles and radiation from one of these jets. NARRATOR: X-ray
astronomer Dan Evans has been tracking the Death Star
galaxy and its violent behavior from the Chandra X-ray satellite
control center outside Boston. DAN EVANS: So we see black
holes do kind of strange things. But only a very small fraction
emit these powerful jets of particles. And a fraction even smaller
such as the 3C321 galaxy, Death Star galaxy, smack into
other combining galaxies. So that's incredibly rare. NARRATOR: The companion galaxy
is across the galactic street 20,000 light years distant. The massive energy beam even
larger than a gamma ray burst from a dying star is firing
nonstop with a seemingly limitless energy supply. [music playing] DAN EVANS: So what
we're looking at here is the best terrestrial analogy
for the Death Star galaxy 3C321. A jet is racing out of
the black hole close to the speed of light. And this actually normally would
propagate up to about a million light years away. But in the special
case of 3C321, the jet is slamming into the
side of a companion galaxy and in doing so is becoming
disrupted and distorted and bent away. And that's wreaking all sorts
of havoc for that companion galaxy. NARRATOR: Much like the building
is deflecting the watershed, the planets and stars
in the victimized galaxy are deflecting most of
the attacking particles. DAN EVANS: So this jet is
actually a massive beam of energy and particles. These particles have
been superheated such that they form a plasma. NARRATOR: Plasma is a mix of
super hot charged electrons and anions funneled into
the jet by the black hole's immense magnetic field. DAN EVANS: So jets that
race out of black holes are actually
incredibly energetic. And in fact, they can
accelerate particles such that they emit light maybe
even up to gamma rays. These rays are
incredibly powerful. NARRATOR: And very long-lasting. Some estimates say the energy
jet from the Death Star galaxy has been firing for
nearly 2 million years. For its fuel, 3C321 simply
devoured an entire galaxy. It's got a lot of fuel. What we actually think
is happening here is that there's been
a previous merger. So another galaxy has fallen
in to the main galaxy. We see this beautiful dust lane,
which implies that the galaxy has been shredded already. And so that act of
shredding drives mass down onto the black hole. NARRATOR: After consuming
another galaxy's provision of plasma particles,
the Death Star galaxy has to somehow energize
the particles into a jet. Black holes have
powerful magnetic fields and super fast spin rays-- a combination that somehow
ignites the particle jet. Scientists believe the reason
the jets fire in one direction has to do with all the dust and
gas circling the black hole. In the case of an
active galaxy like 3C321 which has a supermassive
black hole in the center, you often have a donut or torus
of material surrounding it. In that case, highly energetic
particles near the black hole can't emerge from that
region through the donut along the plane of the galaxy. They can only emerge along this
axis where there's relatively little obstructing material. NARRATOR: Unfortunately
for the companion galaxy, it's staring straight
down the donut hole. And the jet zone of impact is
like the widely scattered blast of a cosmic shotgun. ALEX FILIPPENKO: The problem
with this jet of high speed particles and radiation hitting
the little galaxy 20,000 light years away is that the
jet is wide enough to encompass a large number of
stars in this galaxy. So any creatures
living on any planets orbiting any stars in that
galaxy are in serious trouble right now. NARRATOR: What if it were our
own Milky Way being blasted by the Death Star galaxy? Put Earth in the
path of the jet, and the effect on
the ozone layer would be enormous and deadly. The gamma rays
from the jet in 3C321 convert nitrogen gas
into nitrous oxide. And it's this nitrous oxide
that actually act as a catalyst in the destruction of ozone. So within a matter of weeks
to months, maybe up to a year, the ozone layer would be
completely obliterated. That's a nasty consequence. NARRATOR: But like
many phenomena observed in the universe,
there is a recurring paradox. From death comes life. 3C321 not only destroys. It also creates. It's one of my favorite
things about 3C321 is it demonstrates
really clearly that black holes don't
just gobble everything up in the universe. They're not all complete
harbingers of destruction. The jet that is
coming out of 3C321 is hammering into the side
of the companion galaxy. Yes, of course, that's
a destructive force. But the ultimate legacy
actually is that the gas clouds that get compressed
during this interaction can actually form stars. And the stars can form planets. And the planets
may even form life. So there's this beautiful
cycle of birth and rebirth and destruction that's
synonymous with the universe and black holes. NARRATOR: One day in the
future, our own Milky Way could form its own merger with
the nearby Andromeda galaxy and create a new
Death Star galaxy-- a violent act that
would certainly spell doom for the Earth. Such an event would
likely occur many billions of years in the future. But there are other
stellar threats streaking through our
galaxy at high speed. They are hypervelocity stars. And nothing can stop them. [music playing] To the human eye, stars paint a
tranquil picture in the heavens above. But take an up close look. A select few are death stars
on the verge of extinction. And these cosmic beasts
are anything but peaceful. AMY MAINZER:
Eventually, a star will burn through all the
hydrogen in its core and convert it all to helium. Once it does that, it
has to be massive enough to be able to ignite the helium
and convert helium into heavier elements like carbon,
oxygen, and nitrogen. And this releases an
enormous amount of energy. This process is the same
release of energy that goes on inside a hydrogen bomb. NARRATOR: Though they
are incredibly violent, most of these stars will one
day burn up and slip quietly into the afterlife as
stellar corpses called white dwarf stars-- smallish balls of
electrons and nuclei destined to never
again burn brightly. But some are super
massive stars so energetic they end in a fantastic
supernova explosion and sometimes even produce
the largest of all blasts-- the gamma ray bursts. But for a few
massive death stars, the end is a new beginning. Consider the second
life of a neutron star. When a massive star
explodes in a supernova, its core sometimes collapses
to form a black hole. But much more frequently, if
the core isn't massive enough to create the black
hole, it forms something almost as weird-- a neutron star, a small
but incredibly dense body. CLIFFORD JOHNSON: It actually
has a huge amount of material compressed into a
very small space. So you have, for example,
the mass of our entire sun squeezed into a space maybe only
a couple tens of miles across. The gravity is so strong
that the protons and electrons inside the atoms of the star
are actually pushed together to form neutrons. And a neutron star can remain
stable for billions of years. NARRATOR: Neutron
stars by themselves pose no danger to their
celestial neighbors unless they can find a partner. CLIFFORD JOHNSON: You can also
get another death scenario of the stars where there's
a sort of mutual suicide pact between two neutron stars. NARRATOR: These are called
co-orbiting neutron stars-- a phenomenon initiated
when two neutron stars begin an intimate
but doomed relationship. Their orbit narrows
over millions of years until they finally meet
in a flash of light. And in so doing, they can
generate a violent explosion-- a second life in a sense. There's two different
types of gamma ray bursts. There's short bursts,
which have durations of less than two seconds. And we think that short bursts
are produced by merging neutron stars. NARRATOR: The short bursts are
different than the longer GRBs produced by collapsing
massive stars. The gamma ray burst
emitted by two colliding neutron stars may
be short, but it's powerful-- equal to the energy
released by the sun over its entire lifetime
in less than two seconds. The worry for us? At least two dozen pairs
of orbiting neutron stars exist in the Milky Way. ALEX FILIPPENKO: A very
nearby gamma ray burst first and foremost would get
rid of much of the ozone layer. That could have disastrous
effects on Earth. NARRATOR: Some estimates hold
that a violent neutron star merger occurs within about
3,000 light years of the sun every 100 million years. That's about the same interval
as the mass extinction events recorded in the
Earth's fossil record. Is it coincidence? Or should we worry that the
last tango of two dying stars might eventually blast
the Earth's ozone layer with deadly gamma rays
and alter the planet? Scientists don't
know the answer. The chances are
probably about the same as a runaway star plowing
headlong into the Earth. It's a remote possibility
but fearsome to contemplate. CLIFFORD JOHNSON: You can
actually have the possibility that a collection of stars
that perhaps were all together in the same neighborhood
interacting with each other sometimes ejects a star just
to wander off on its own. As far as we know, there are no
wandering stars headed our way. But if that were to happen,
it could be quite interesting. NARRATOR: One scenario
could see the Earth's orbit around the sun disrupted
by the gravitational pull of the wandering star. CLIFFORD JOHNSON: One
dramatic possibility is that such a wandering star
simply kicks the Earth entirely out of the solar system. And so we're now
wandering around without a source of energy-- the sun. No one really knows
what would happen. It really depends upon the
angle of approach, the mass of the star, et cetera. NARRATOR: Wandering
stars can travel up to 60 miles per second-- fast but still not fast enough
to escape the Milky Way's gravitational pull. But there are some
supercharged turbo models that could actually
break free and rocket out into the universe. These are called
hypervelocity stars. Hypervelocity stars are
normal stars like the sun, except that they're
moving out of the galaxy at well over a
million miles an hour. And that's beyond the escape
velocity of the Milky Way. NARRATOR: The need for speed
begins with a normal pair of co-orbiting stars that
get too close to the edge of a black hole. Just as the disabled
Apollo 13 command module got a boost of velocity
by maneuvering close to the moon's orbit,
the hypervelocity star gets a huge gravitational
kick from the black hole, severing the bond with
its binary partner. WARREN BROWN: [inaudible]
closest to black holes captured into a very tight orbit
around the black hole. And so it loses this energy. The other star gains that energy
and is ejected with this very large velocity as a result. NARRATOR: The ejection
of a hypervelocity star is much like a slingshot effect. At the instant the binary
star's orbit is broken, the hypervelocity star is
launched with incredible force into the void of space. WARREN BROWN: They've been
booted out of the Milky Way. And they're destined to
drift into the [inaudible] depths of intergalactic space. It's very unlikely that
these stars will ever affect the Earth. NARRATOR: Fortunately,
the eventual death of these speedy stars will occur
far away from our solar system. It's the death stars
on our own block we need to keep an eye on. In cosmic time,
their fuses are lit. And we have a front row
seat to their annihilation. [music playing] In remote corners
of the universe, countless stars are biding their
time on death row sentenced to spectacular violent endings. Closer to home, there
are a few dozen stars within 20 light years of the
Earth, and a few of these are preparing for death. ALEX FILIPPENKO: I think
we're safe from the dangers of a normal supernova. In the case of a gamma ray
burst, we're not so sure. NARRATOR: One is in
the stellar system Eta Carinae, a
super massive star about a hundred times bigger
and a million times more luminous than the sun. In 1843, a buildup of pressure
ignited a gigantic eruption of light seen from Earth. But the star survived and formed
a dust cloud called a nebula. At a distance of just
8,000 light years, we'll have a front row
seat to its annihilation. We think it's going to turn
into a black hole sometime between now and the
next million years. And as it collapses,
it has enough matter that it can produce a
powerful gamma ray burst. NARRATOR: Unlike the
star Wolf-Rayet 104, Eta Carinae doesn't have
us in its crosshairs. We know that the
rotation of Eta Carinae is not pointed towards Earth. So lucky for us, the
pulse of the gamma ray is not going to be
directly impacting Earth. NARRATOR: When it happens,
the explosion will likely be the brightest supernova
ever witnessed by mankind, unless the title goes to another
death star contender that's even closer to Earth-- Betelgeuse. Located in the
Orion constellation about 500 light years
away, Betelgeuse is quickly burning through
the last of its nuclear fuel. ALEX FILIPPENKO: Betelgeuse is
a very massive star about 20 times the mass of the sun. And it's within half a
million years of exploding. People have been noticing that
Betelgeuse has been changing a lot over the last decades. It's actually shrunk
considerably, about 15%. What that means, no one is sure. But everyone's
keeping an eye on it. NARRATOR: Some scientists
believe Betelgeuse could unleash a gamma ray burst. People on Earth have
little to fear if it does. Like Eta Carinae,
the star's axis points safely away from Earth. Not only that, but Betelgeuse
may also have a built-in blast shield. ALEX FILIPPENKO: Its explosion
will be relatively normal. It won't be a gamma ray burst. Because there is this
thick hydrogen envelope in Betelgeuse. And that hydrogen
envelope will probably prevent the jet of particles
and radiation from emerging. There's too much
material through which the jet of radiation
would have to pass. NARRATOR: Betelgeuse will shine
intensely for a brief moment. But it won't compare to the
final moments of our nearest star, the sun. AMY MAINZER: Average
stars like our sun have nice, long lifespans
fortunately for us. And our sun is about halfway
through its 10 billion year lifetime. So it's about 4 and
1/2 billion years old. That makes it middle-aged. NARRATOR: Scientists estimate
that the sun will live another 5 billion
years, but our problems could begin much sooner. Our own sun is very
gradually getting brighter, getting more powerful. And within a half a billion,
certainly a billion years, the Earth will become so hot
that the oceans will have evaporated away. So we don't quite have
4 or 5 billion years to worry about this problem. We have to worry about it
on timescales of hundreds of millions of years. NARRATOR: Billions of years
after the sun renders the Earth devoid of life, it will
enter a final phase known as a red giant. It can't explode and produce
a supernova because it's not massive enough. But most scientists agree
on the final chapter. As a red giant, its
density will decrease, and the sun will balloon
outward, devouring its nearest neighbors. AMY MAINZER: At this
stage, the red giant stage, the sun will probably expand
and engulf Mercury, Venus, and maybe even Earth itself. So that would pretty
much be the end of Earth. NARRATOR: Of all the dangerous
death stars in the universe, the one most likely to destroy
the Earth is our own sun. While it marks our
planet's ultimate end, it's merely a part of
the cycle of creation. Death stars take life, but they
are also the origin of life. ALEX FILIPPENKO: The heavy
elements in our bodies quite literally were generated by
previous generations of stars and ejected into the cosmos
by stellar explosions. So we would not be here if
it were not for the fact that some stars
explode violently at the end of their lives. As Carl Sagan used to say,
we are made of star stuff. We are made of stardust. NARRATOR: As the
explosions continue, the resulting heavy
elements may one day reseed the very
foundations of life far from the Milky Way on a
new blue planet in a new corner of the universe.
