The Universe

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 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."

This isn't your neighborhood,

neither is this

or this

or any of these.

And it isn't even this.

Looked at from a wider perspective,

your neighborhood is a big cloud of gas.

Astronomers say the solar system is moving through

the local interstellar cloud,

also called "the local fluff"

because of its low density and irregular shape.

The gases are mainly hydrogen and some helium.

There are trace amounts of heavier atoms

like carbon and oxygen and nitrogen

that are just floating around the interstellar medium.

We know that the heavier atoms in the interstellar medium

are left over from previous explosions of stars

as supernovae.

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.

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.

= turn left in 30 feet.

Narrator: But when you're dealing with something

as big as the milky way,

GPS isn't an option.

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

Narrator: Even exploring our local neighborhood

involves a lot of uncertainty.

But if we did have a galactic positioning system,

it would probably locate us about midway between

the top and bottom of the milky way

and about midway between the galaxy's outer edge

and inner core.

Our solar system is about 26,000 light-years away

from the center of our galaxy.

Narrator: According to one hypothesis,

we have a very exclusive location.

There is one idea that only stars in a certain range

of distances from the center of our galaxy

are in the so-called galactic habitable zone,

that is, able to have life on planets

surrounding those stars.

It is just the right place

with a star of the right temperature

and a planet at the right distance

for there to be a lot of liquid water on the surface,

where the chemistry of life began and evolved into us.

Narrator: The overall range of the galactic habitable zone

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

from the center of the milky way.

The main part, where we are,

ranges from 20,000 to 29,000 light-years from the core.

Inside the zone,

old neighborhoods have been destroyed

to make a place we can call home.

Depending upon how you look at things,

our local neighborhood, our local solar system,

is actually a relatively safe place

compared to what seems to be going on

f 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 were all sorts of collisions

and violent things happening

that gave rise to this nice, calm-...

Or relatively calm place that we have today.

We think that the earliest stars formed

out of hydrogen and helium alone,

but that, over time, the stars work as these processors

that create the heavier elements.

This is important because when those stars

eventually die and explode,

these supernovae, or stellar death explosions,

seed the galaxy and the material around it

with heavier elements.

So for example, the carbon in our cells,

the oxygen that we breathe,

the calcium in our bones,

the iron in our red blood cells,

all those are heavy elements.

We know that the sun

is at least a second- or a third-generation star

because there are planets around it.

There are things made of iron and carbon

and other heavier elements.

Narrator: But the processes that led to life on earth

don't seem to exist outside the zone.

Closer to the edge of the galaxy,

fewer massive stars have exploded,

producing fewer heavy elements.

Further out in the galaxy,

you don't have as many atoms like carbon, nitrogen, oxygen-

the atoms that are so important for the chemistry of life.

So the habitable zone of the galaxy

cuts off at a distance where you just won't have

the heavier atoms to make life.

Narrator: If the outer galaxy is a bad neighborhood,

the inner area is even worse.

Gravity from massive gas giant planets

could tear us apart.

And there are other dangers the closer you get

to the galactic core.

Back in the times of copernicus,

we thought that we were the center of our universe,

and even as we started to learn more about the heavens,

eventually, we still thought that we were the center

of the galaxy.

Now that we know even more, though,

it actually turns out that we're lucky

we're not in the center of the galaxy.

Narrator: At the center of the milky way,

sucking matter and even light into it,

is sagittarius a-star,

a black hole nearly 14 million miles across

with a mass 3.7 million times that of our sun.

If the galactic center has a black hole in it,

it gives off a lot of radiation-

enough to fry life as we know it-

so you can't be too close to that.

Then there are other regions in the galaxy

that are also probably not so great for life

because there's just so much radiation

from nearby really hot o-type stars.

Narrator: O-type stars are giants.

They're hotter than the sun,

10 to 50 times as massive,

and throw out Titanic amounts of ultraviolet radiation.

With these stars, you don't worry about sunburn

but extinction.

It's probably not easy to survive in an environment

where you're in a tight cluster with a lot of o-type stars.

Narrator: O-type giants can destroy planets

before they form.

The radiation from these stars is so strong

that it actually sweeps the material away

from these newly forming, would-be planetary systems

and rips it out of the orbit of their stars.

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

It's 5,200 light-years away, far outside the local bubble,

but it shows what o-type giants could do to our neighborhood.

A 2008 study by the university of Arizona

of 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.