All language subtitles for The Universe S01E10 Life and Death of a Star

In the beginning, there was darkness,
and then, bang, giving birth to an

expanding existence of time, space, and
matter.

Now, it's further than we've ever
imagined, beyond the limits of our

in a place we call the universe.

Each star you see twinkling in the night
sky.

is a luminous sphere of superheated gas
much larger than any planet.

And each has a story to tell.

A traumatic birth.

A life on the edge.

Gravity collects the star in the first
place, and then gravity wants to crush

it. And a death that rattles the
heavens.

The whole thing goes off in a blinding
flash. The biggest explosion in the

universe.

the universe at its most volatile and
action -packed life and death of a star.

Like glittering cities in the desert,
galaxies arise

out of the great darkness of the
universe.

Galaxies made of billions of blazing
lights called stars.

There are billions and billions of
stars.

In fact, in our galaxy, there are 400
billion stars, just in our galaxy.

But how were these stars born?

How will they die?

And how can it be that all human beings
on Earth owe their lives to the death of

stars?

The quest for answers begins here, in a
cloud of dust and gas, hovering in the

interstellar desert.

You are looking at the Pillars of
Creation.

The Pillars of Creation are a stellar
nursery.

New stars are in the process of being
born in the central region.

Located 7 ,000 light years from Earth,
the pillars are part of the Eagle

which is just one of billions of star
-forming regions in the universe.

The pillars are towering clouds of dust
and hydrogen gas.

If you remember the periodic table of
elements from chemistry class, you have

the light elements up at the top,
hydrogen, helium, lithium, this sort of

and then the really heavy ones as you
get lower down.

It's hydrogen the lightest simplest most
abundant element in the universe that

is the key component of stars Within a
nebula clumps

of this gas and dust slowly coalesce
into smaller clouds over millions of

Pulled together by a very familiar force

The same

force that connects us here to the
Earth, it keeps us on the Earth. Gravity

the same force that pulls things
together in a way that gives us planets

stars and galaxies in the universe.

Gravity in many senses is the most
important force in astronomy.

And when gravity acts in the universe,
one of the basic things that it produces

is stars.

Stars are sort of the most basic unit of
mass that is produced when gravity

pulls mass together.

Each contracting cloud can produce
anywhere from a few dozen to thousands

stars.

To form a star like our sun, which is a
million miles across, it takes a clump

of gas and dust a hundred times the size
of our solar system.

These clouds start off their lives
bitterly cold, with temperatures

degrees below zero Fahrenheit.

But as gravity fragments and compresses
them, the heat begins to soar.

Within a few hundred thousand years, the
cloud spins into a flattened disk.

Gravity coalesces the center of the disk
into a sphere, where the heat rises to

a scorching two million degrees.

This glowing system is now known as a
protostar.

Ten million years later, the searing
hydrogen core of the fledgling star

past 18 million degrees, and something
incredible happens.

The core becomes so hot it can sustain
thermonuclear fusion.

Thermonuclear fusion.

It's a lot of syllables, but it just
means it's hot there, and small atoms

become big atoms.

Hydrogen atoms are moving fast enough
that they actually...

will fuse together and will form a
helium atom.

It's this nuclear reaction that produces
the energy to power the star throughout

its life, giving it a constant source of
light and heat.

It's self -luminant, generates its own
heat, and that's the essence of what

makes a star a star.

If you've got fusion, you've got a star.

Once born, a star's life will be a
constant battle.

An all -out war against gravity.

Gravity collects the star in the first
place, and then gravity wants to crush

it. Gravity never gives up. Gravity
wants to pull everything together.

And so if the star is going to have a
life, and a long life, it has to find a

way to fight against gravity.

You feel gravity all the time when you
try to jump or try to climb a rock.

There's always gravity pulling you back
down.

And in order to fight against gravity,
you have to have some way of applying a

force which works in the opposite
direction of gravity.

So if there's a rope, you can use your
muscles to pull on the rope and

resist and even overcome gravity.

But that doesn't mean gravity gives up.

Gravity is always working.

And so you have to keep applying this
force in order to not fall off.

And if you give up or let go or the rope
breaks, gravity immediately wins and

you fall.

The same kind of thing happens with
stars.

Stars are also trying to hold themselves
up against gravitational collapse.

Gravity wants to crush the star down to
the middle.

For stars, nuclear fusion provides the
rope in the form of pressure.

The heat gets all the particles in the
star moving around quickly and they bang

outwards and that produces a pressure.

which can actually hold the star up
against gravity.

The amount of pressure pushing out on
the star just matches the amount of

gravity pulling in on the star, and it
can sit there and burn happily until

something changes.

A star will spend most of its life in
this state of equilibrium.

It's a phase scientists call the main
sequence.

So our sun is in the main sequence.
We're very happy it's in the main

It provides the same amount of energy
almost every day.

And that's what makes life possible.

All stars on the main sequence aren't
alike.

Some are much smaller and cooler than
the sun.

Others much larger and hotter.

So it turns out that how hot something
is is related to the color of the light

that it emits. So a star like the sun...

Most of the light that comes out from
the sun is sort of a yellow -type color.

If the sun were much hotter, the
predominant wavelengths of light would

into the blue, or even into the
ultraviolet, and cooler stars emit more

light.

Small, cool red stars, like Proxima
Centauri, the nearest star to the sun,

known as red dwarfs.

They can be as little as one -tenth the
mass of the sun.

With surface temperatures thousands of
degrees cooler, red dwarfs are the most

common type of stars in the universe.

There are many, many more of these sort
of very dim red dwarfs floating out in

space than there are stars like the sun.

Now, of course, when you look in the
night sky, you don't see the most common

kinds of stars. You don't see these red
dwarfs because they're so faint.

You merely see the very rare, very
bright stars that turn out to be very,

far away.

On the opposite end of the spectrum are
the large blue main sequence stars.

Averaging a surface temperature of 45
,000 degrees Fahrenheit, they can be 20

times the mass of the Sun and 10 ,000
times more luminous.

In the life and death of a star, size
definitely matters.

Mass is the fundamental thing which
drives the life history of a star.

the more massive stars live much shorter
lives than the less massive stars.

And that's perhaps a little bit strange
sounding, because the massive stars have

more fuel to burn. You'd think they'd
live longer.

So it's counterintuitive that more
massive stars will burn through their

more quickly than the lower mass stars.

Imagine two gamblers sitting down at a
blackjack table.

You would expect the one with the most
money, the most fuel to burn, would last

the longest.

But what if the big -time gambler is
making huge bets on every hand?

A gambler that is gambling with a lot
more money and putting down $10 ,000 at

time is going to burn through that money
much more quickly.

And so the more mass you have, the
higher temperature, the higher pressure,

higher the fusion rate. And it goes much
more quickly with the more mass you

have.

And it's always just simply the
calculation. How much fuel do you have,

what rate are you converting it?

The high -mass stars live their lives
faster.

They burn their candle at both ends.
There's life in the fast lane.

A high -mass star could die within a
million years.

A star ten times as massive as our sun
might live for only one one -thousandth

as long.

So our sun will live for about ten
billion years in total.

A star ten times as massive as our sun
might live only ten million years in

total.

While massive stars have lifespans
measured in millions of years, The

mass stars measure their lives in tens
of billions, if not trillions of years.

Every low mass star that has ever been
born in the universe, and the universe

has been making stars for more than 10
billion years, all of those stars are

still in their infancy.

No such star that's ever been born has
ever come close to dying.

But for all stars, including our own
sun, life on the main sequence can't go

forever.

It can only last as long as the star has
fuel to burn. If it runs out of fuel,

fusion stops and gravity wins.

Gravity never gives up, whereas fuel, of
course, can run out after a while.

And so the star and the climber both
have this terrible problem that if they

don't maintain their fight against
gravity, they will end in a death, a

cataclysmic death.

Not only does the size of a star
influence how long it will live, it also

determines how it will die.

Massive stars explode from the seed in
violent fury, while smaller ones are

doomed to slowly fade away.

For five billion years, our sun, a lower
-mass, middle -aged star, has been

happily burning through its supply of
hydrogen fuel.

Like a gambler slowly plowing through a
pile of chips.

The gambler may sit there for a long
period of time, just like a star burns

hydrogen for a really long period of
time. However, at some point, he's going

run out of money.

Scientists predict that five billion
years in the future, our sun will reach

this critical crossroads.

Its supply of hydrogen fuel will have
been completely exhausted.

nuclear fusion will cease and gravity
will begin to crush the star.

At that point, the situation is
desperate.

In order to survive, a sun -like star
must find a new source of fuel.

It has helium on hand, but in order to
start burning helium, the core has to be

ten times hotter than it was during its
lifetime burning hydrogen.

It won't be able to fuse that helium
into heavier elements like carbon and

oxygen until the core gets sufficiently
hot.

And that's because it's harder to get
the helium nuclei close enough together

for the strong nuclear force to take
over, grab them, and cause them to fuse

together.

As it continues to contract inward,
nature throws the star a lifeline.

The core actually becomes superheated by
the very gravitational pressure that's

trying to crush it.

When it reaches 180 million degrees, it
can start fusing helium into carbon in a

desperate gamble to survive.

So the desperate gambler might go take
out a loan on their house and get more

money. But in getting more money to burn
through, it's really just delaying the

inevitable, which is to go bust.

And for a star, the inevitable is to
die.

The star, which took 10 billion years to
burn through its hydrogen, now powers

through its supply of helium in a mere
100 million years.

And then the action begins.

It runs out of hydrogen, starts fusing
helium.

Runs out of helium, attempts to fuse
carbon and will fail. But all the

all the, well, what's going on now?

happens in the last 10 % of a star's
life.

The searing heat of the helium burning
actually causes the outer layers of the

star to swell.

At that point, the outer atmosphere of
our star will be held in by gravity so

weakly that it'll start sort of just
evaporating away.

through a series of what I call cosmic
bursts, it will actually eject the outer

envelope of gases, which are only weakly
held by gravity.

That'll send some shells of gas outward,
illuminated by the hot central star.

And that will cause what's called the
planetary nebula phenomenon.

Beautiful shells of glowing gas
surrounding the dying core.

of our sun with the core unable to
muster any more nuclear fusion can it

possibly survive gravity's crushing grip
as a star the size

of our sun died it ejects its outer
layers with no nuclear reactions to

outward pressure gravity gains the upper
hand the star begins to fall in on

itself like a climber too tired to hold
on to his rope There's one possibility

that the rock climber might be able to
use if he gets too tired to hold on to

the rope anymore, and that is if he can
find a ledge on the rock that he's

climbing.

Gravity can pull on him all he wants,
but the ledge itself will support him

against gravity, and he doesn't have to
provide any more energy to win his

fight.

There's a certain kind of star, and our
sun is actually an example of this,

where the star finds that it has an out.

in this fight against gravity.

The contracting star finds its ledge in
a surprising place, electrons, tiny

negatively charged atomic particles.

Electrons don't like being compressed so
that they're very close to one another

because electrons effectively don't like
each other.

If you compact the electrons hard
enough, the pressure of the electrons

themselves

is able to hold up the star against
gravity.

When the core of our dying sun -like
star is crunched to about the size of

Earth, this so -called electron
degeneracy pressure takes over.

Gravity can collapse the star no
further.

It's left to slowly cool into a bizarre
stellar remnant known as a white dwarf.

Like this one, Sirius B, which can be
seen only faintly aside its companion,

Sirius, the brightest star in our sky.

Now, a white dwarf is a very strange
type of star.

It's very, very dense.

The white dwarf has about 300 ,000 times
the mass of the Earth,

compressed into a volume the size of the
Earth.

If you had just a teaspoonful of
material, it would weigh several tons.

So it's really amazing stuff.

A white dwarf is the final stage in the
life of a sun -like star.

But it's not quite dead yet.

It will continue to shine for billions
of years as it gradually radiates away a

lifetime of energy.

I like to call white dwarfs retired
stars in the sense that...

All of the light that they are shining
is energy that they accumulated during

their normal lives as stars while they
were fusing light elements into heavy

elements, as our sun is doing right now.
So it's spending its life saving. It's

a retired star.

That will be the fate of our sun.

But some white dwarfs can have one last
hurrah.

thanks to a friend who lends a helping
hand.

Because although our sun is a cosmic
loner, more than half of all stars

through life with at least one
companion.

Most stars are members of binaries or
possibly even multiple star systems.

Close binary stars can have very
different fates from your ordinary

stars.

If a white dwarf is gravitationally
bound to another star as part of a

system, it can essentially steal the
lifeblood from its companion.

The small but dense white dwarf exerts
such a strong gravitational pull that it

will start siphoning off a stream of
hydrogen gas.

If it gathers material from a companion
star and it is able to grow in mass,

then eventually...

the mass of the white dwarf can reach an
unstable limit, roughly 40 % more than

the mass of our sun.

At that point, the white dwarf undergoes
a catastrophic explosion,

where the whole thing goes off in a
blinding flash, what's called a

thermonuclear runaway of the entire
star.

This mammoth explosion is known as a
Type 1a supernova.

So if our sun were to do this, and it
won't, it'll die in a relatively quiet

way. But if it were to do this, you'd
need sunblock or supernova block of a

billion in order to protect yourself
from the blinding flash.

University of California, Berkeley
astronomer Alex Filippenko.

is one of the world's most successful
supernova hunters.

His team has found over 600 of them in
the past decade.

An incredible feat, considering they
occur perhaps twice per century in each

galaxy.

Searching for supernovas is akin to
scanning a crowded football stadium with

binoculars in hopes of catching the one
person who might be taking a flash

photograph at a given point in time.

If you were to look at each person
individually, one by one, you would have

hard time finding the person who happens
to be taking a flash photo.

Filippenko increases his odds by
expanding his search beyond single stars

even single galaxies.

To do this, he enlists the help of a
very high -tech assistant.

This is a robotic search engine for
exploding stars, supernovae.

It has been programmed.

to robotically take photographs of over
a thousand galaxies a night, and over

the course of a week it does seven or
eight thousand galaxies, and then it

repeats the process, comparing the new
pictures of each galaxy with old

pictures. Now, usually there's nothing
new in the new picture, but occasionally

a star blows up, a supernova goes off,
and then you can see in the new picture

bright... point of light that wasn't
there in any of the old pictures.

Though a supernova is visually very,
very bright, the visible light is only

1 % of 1 % of the total energy, 1 ten
-thousandth of the

entire energy emitted by this colossal
explosion.

Although Type Ia supernovas come from
exploding white dwarfs,

Many others, known as Type II
supernovas, signal the dramatic death of

massive stars, perhaps eight or ten
times more massive than the Sun.

Unlike their smaller cousins, when
massive stars exhaust their hydrogen

they have the raw power to start fusing
other elements.

The ashes of each set of nuclear
reactions become fuel for the next, so

near the end of its life, A massive star
resembles an onion in cross -section,

with an outer layer of the original
fuel, hydrogen, surrounding layer after

layer of heavier and heavier elements.

It goes through its normal life, fusing
hydrogen into helium, then helium into

carbon and oxygen, then oxygen into neon
and magnesium, and then silicon and

sulfur.

And then iron.

The massive star builds up a core of
iron.

The fusion of iron into heavier elements
doesn't do the star any good. It

doesn't keep the star hot inside because
fusion of iron into heavier elements

requires energy. It absorbs energy.

It doesn't liberate energy.

So the iron core builds up without
fusing and eventually becomes unstable.

When it reaches something like one and a
half times the mass of our sun, it

collapses.

And the collapse is violent.

Within half a second, a core the size of
the Earth is crushed into an object

roughly 10 miles across.

For a moment, the collapsing core
rebounds, smashing into the outer layers

the star and kicking off one of the most
massive explosions in our universe

since the Big Bang.

The collapse of the iron core.

blows apart the rest of the star in a
colossal explosion.

It's truly an amazing, incredible event.

Scientists are convinced that supernovas
mean much more to the universe than

spectacular light shows.

They are, in fact, the source of the
heavy elements that make up everything

around us.

Iron in this foundry came from exploding
stars, from gigantic explosions.

All of it, all the iron you see
everywhere, came from exploding stars.

And in fact, all the elements heavier
than iron, directly or indirectly, were

made by exploding stars.

And those elements were ejected into the
cosmos by these gargantuan explosions.

As material from these explosions spread
out through the universe, it became the

stuff of planets, moons, new stars and
something even more extraordinary.

If you could trace your ancestry back to
its earliest reaches, you would find an

exploding star in your family tree.

We are essentially made of star stuff or
stardust, as Carl Sagan used to say.

The elements in your body, not just
generically, but specifically, the

in your body heavier than hydrogen and
helium came from long dead stars.

The calcium in your bones, the oxygen
that you breathe, the iron in your red

blood cells, the carbon in most of your
cells, all those things were created.

in stars through nuclear reactions and
then ejected by supernovae. And the

heaviest elements, iron and above, were
produced by the explosions themselves,

by the supernovae.

While the explosion of a Type II
supernova showers the universe with

elements, the core of the exploding star
is left intact, destroying that.

is gravity's job.

But to crush the core any smaller than
the size of a white dwarf, it will have

to overcome that strange force, electron
degeneracy pressure.

Gravity actually finds a way of
defeating that tendency the electrons

push each other apart by combining the
electrons with the protons and turning

them into neutrons.

You now have an object which is made
almost entirely out of neutrons, and

gravity wins. It now allows...

the system to collapse.

Further, they're no longer electrons
stopping that, and gravity seems to win,

except neutrons, it turns out, also
don't like each other, and you end up

new stable object, even smaller, even
more dense, called a neutron star.

Compared to normal stars, neutron stars
are cosmic pebbles.

They can be as small as 10 miles across.

So imagine you take a star about one and
a half times the size of our sun, and

then you compress all of that material
down into a very small space, about the

size of Manhattan.

You've just made yourself a neutron
star.

Squeezing that amount of mass into such
a small space makes for an extremely

dense object.

One teaspoonful of neutron star material
would weigh a billion tons.

Neutron stars are some of the most
exciting and weird objects in the

that astronomers study.

If a human being would stand on a
neutron star, it would be a somewhat

uncomfortable experience.

On Earth, if they weighed about 150
pounds, on a neutron star they would

something like 10 billion tons.

Biology can't stand that amount of
pressure, and so a human being would

essentially be squashed flat against the
surface of the star.

In addition to that, Neutron stars are
spinning at an incredibly high rate,

hundreds of times per second in some
cases.

It's this rapid spin that enabled
astronomers to first identify neutron

Some neutron stars are spinning really
rapidly, and they have a really

high magnetic field.

That magnetic field, together with the
spin,

forces a bunch of charged particles,
electrons, to go along the axis of the

magnetic field.

And those accelerated electrons give off
light.

They produce a well -focused beam of
light.

Now, this is like a lighthouse whose
beam is always on, but you only see it

the lighthouse beam intersects your line
of sight.

In a similar way, we might see the
shining neutron star only when the beam

points at us.

That object is called a pulsar.

Some stars are so massive, perhaps 25 or
40 times the mass of the sun, that not

even a neutron star can hold up under
the weight of their collapse.

And gravity will crush them even further
into an object of infinite density and

almost equally limitless fascination.

A black hole.

In some sense, a black hole represents
the ultimate death of a star.

A black hole is basically gravity's
victory over mass.

It is complete collapse of a star, a
very massive star.

This collapse creates a region of space
where matter is compressed into such a

high density that its gravitational
field is inescapable.

Black holes are remarkable in that
nothing can escape from them, not even

fastest moving thing we know of, which
is light.

You shine a flashlight beam up and even
it won't leave. The beam will curve

back around so you won't be able to see
it from the outside, hence the name

black hole.

A common misperception is that black
holes just go sucking up everything in

universe.

Just like cosmic vacuum cleaners sucking
up everything in their vicinity.

That's actually not true.

Now, objects that are very close to
black holes do get sucked in.

But if you're comfortably far away with
the proper trajectory, you won't get

sucked in.

Scientists have long suspected that
there is yet another class of supernova

involving even bigger stars and even
more powerful explosions.

Stars that collapse so catastrophically,
that they leave behind no remnant, not

even a black hole.

But no one had ever seen one until now.

Even after billions of years, the
universe is still surprising us with its

power. In the fall of 2006, astronomers
observed the largest stellar

explosion ever witnessed by man.

240 million light years away from Earth,
a massive star blew itself apart.

Alex Filippenko and his team at the
University of California, Berkeley, were

amazed at the power of the explosion.

And the total energy emitted was 100
times as much as the energy of

a normal massive explosion.

It's an amazing, really powerful
explosion.

A normal supernova comes from the
explosion of a star ten times more

than our sun.

Incredibly, supernova 2006 GY, as
astronomers have dubbed it, seems to

signaled the death of a star 150 or even
200 times more massive.

That's about as massive as a star can
get.

Scientists are still studying the
aftermath of the explosion, but they

Supernova 2006 GY has a lot to teach us
about the first stars that populated our

universe.

We actually think that the first
generation of stars tended to be really

massive, and they probably exploded by
this mechanism.

It's these mega explosions that likely
seeded the early universe with heavy

elements.

These extremely massive stars are the
largest iron factories in the universe.

A single star, 150 times the mass of the
sun, can produce 20 or 25

solar masses of iron. It's incredible.

In the cycle of life, not only here on
Earth, but in the cosmos, as stars die,

particularly those that die spectacular
deaths, the high -mass stars that

manufactured heavy elements in the core,
those give the seeds of the next

generations of stars that then increase
the likelihood that that next generation

will have planets, and planets that
contain the ingredients of life itself.

Supernovas aren't the only energetic
events in the life and death of a star.

Right now, across the universe, there
are a thousand pairs of stars engaged in

brilliant dances of fire.

For some, this dance will end in
catastrophe.

Astrophysicist Joshua Barnes of the
University of Hawaii studies what

when stars collide.

We don't have the luxury of watching
stars collide.

A pair of stars, if they draw close
enough to collide, would just be a

dot of light, even in the largest
telescopes that we have.

So we need to investigate these things
with a computer.

Using computer models, astrophysicists
can take any two types of stars and find

out what happens if they become involved
in a stellar smash -up.

The models pose hypothetical situations
and then see what happens.

And you could sort of imagine this is
like studying collisions of cars, and

were taking them out and smashing them
together in the parking lot, one after

the other, to see what came out of them.

Among the most explosive collisions
modeled by astrophysicists is the clash

two orbiting neutron stars.

Typically, they're bound together as a
pair orbiting one another, and as they

orbit, they disturb the space that's
around them and create waves of energy.

And the energy to do that slows the
stars down so they get closer and closer

together. As they get really close
together, they're orbiting around

even a thousand times per second. The
final event is very dramatic.

When two neutron stars collide, they're
moving at nearly the speed of light.

Although the final collision takes only
a fraction of a second, it unleashes

more energy than the sun will generate
in its entire lifetime.

Thanks to computer modeling, we can also
predict what would happen if a highly

dense white dwarf collided with our sun.

It would be a frightening collision.

When it got close enough, the
gravitational fields of the white dwarf

start to distort the sun, so the sun
would no longer remain a sphere. It

sort of turn into an egg shape as the
thing came close.

As the white dwarf plows into the sun at
supersonic speed,

Its gravity would send an enormous
shockwave throughout the star.

And that would produce so much
thermonuclear energy to essentially

sun.

Amazingly, it would take only about an
hour for the white dwarf to plow through

the sun and annihilate it.

If this scenario came to pass...

Life on Earth would be doomed.

Fortunately, the chances of this
happening are slim because the sun is in

uncrowded part of the Milky Way galaxy.

Individual stars are kind of jostling
and weaving as they make their great

circuit around the galactic center.

So it's a complicated traffic situation.

But because the space between the stars
is so great, there's not much chance of

a collision.

If you were to wait out here on this
beach until you saw that collision

the sun and another star, you would wait
a long time.

Even over its entire life, the sun has
probably a billion and one chance of

colliding with another star.

But there are places within galaxies
where the odds of a collision are much

greater.

Regions where hundreds of thousands or
even millions of stars are crowded

together by gravity into a globular
cluster.

Compared to the spiral arms of the Milky
Way, a globular cluster is like a

demolition derby.

The odds of two stars colliding in the
spiral arms of our galaxy are only about

one in a billion.

But within a globular cluster, stars are
packed a million times more densely

than elsewhere in the Milky Way.

In the Milky Way, everybody is pretty
much going in the same direction.

But in a globular cluster, there's no
organized motion.

They're basically all orbiting around
the center on orbits which are aligned

all sorts of different directions.

So some are going one way, some are
going the opposite way.

In these crowded, chaotic conditions,
stars collide on average once every 10

,000 years.

Every star in a cluster was born at
roughly the same time. So when

look at an old cluster, they don't
expect to see any young stars.

But strangely, a globular cluster
usually conceals some mysterious

Large blue stars, far younger than the
small dim stars surrounding them.

These seemingly impossible stars are
known as blue stragglers.

The mystery of blue stragglers is that
they're in some sense younger than they

have any right to be.

All of the stars of that mass and that
luminosity would have died off billions

of years ago in these clusters.

So the puzzle is, where did these things
come from? How did they get into these

star clusters?

Astrophysicist Joshua Barnes thinks he
knows the answer.

He believes blue stragglers are the
result of collisions between older,

main -sequence stars.

A collision of two main sequence stars,
two sun -like stars, is actually

relatively gentle.

The mutual gravity of the stars locks
them in a spiral.

They've lost energy of motion and they
will come back and have multiple

subsequent passages.

They heat up and swell up and kind of
spiral around each other, making several

passes, each closer than the last one,
until they finally come together and

start to merge.

In the end, rather than triggering a
catastrophe, the two stars merge to form

one more massive star.

What you're basically doing is taking
two small old stars, piling them

to make one star now, which is twice as
massive, and therefore being more

massive, it's brighter and bluer than
the rest of the stars in the cluster. So

it seems to be straggling behind the
rest of the stars.

While the mystery of the blue stragglers
seems to have been solved, the heavens

are bursting with unusual objects that
dare science to explain them.

Black holes, neutron stars, and white
dwarves all represent the end of

remarkable stellar lives.

But there are other strange celestial
objects that never got a chance to

Not quite planets, not quite stars.

These are the brown dwarfs.

Brown dwarf is basically a failed star.

University of Hawaii astronomer Michael
Liu searches for these elusive objects.

Stars produce a lot of light. They're
very easy to see a long ways away.

But brown dwarfs are very low
temperature, and so they emit very, very

light.

Because they're so dim, it means we can
only see them if they're very close to

us.

A brown dwarf has the same ingredients
as a star.

but it simply doesn't have enough mass
to sustain nuclear fusion.

If something is born with less than 8 %
the mass of the sun, then it can't

produce its own energy. It's essentially
a failed star.

Without fusion, these failed stars start
to act more like planets.

If you were flying in a spaceship across
the surface of a star, you wouldn't

really see anything that looked like
clouds or mountains or anything like

When you go to a brown dwarf, things
begin to change.

We think their atmospheres in some ways
might be similar to things like very

massive versions of the planet Jupiter.

If you're familiar with pictures of
Jupiter, you see Jupiter has all sorts

banding structure and clouds on its
surface.

Although we've never taken a picture of
the surface of a brown dwarf, we think

brown dwarfs may also have similar cloud
structure.

Now these aren't normal kinds of clouds
like we know about on the Earth.

You have iron vapor making these clouds.

and then the clouds may get thick enough
that you get iron droplets raining out

of the cloud.

Obviously, a person wouldn't want to be
there because these are molten iron.

To date, astronomers have located only a
couple hundred brown dwarfs, and they

still have many questions about these
elusive objects.

For one, they know some brown dwarfs
have disks of dust and gas around them.

Might those disks form into planets?

That's just one of many mysteries yet to
be solved as we continue to probe the

stars.

But already, science has revealed the
universe to be a magical realm of dwarfs

and giants, stragglers and supernovas.
And hidden within the explosive life

story of stars, they have found the very
history of the cosmos and a key to

understanding our own origins.