(phone ringing)
- Hi, it's Doug!
This is the first ever real
photograph of a black hole.
Now, seeing this makes me think
of all kinds of questions,
like why haven't we been able
to take a photograph of this before?
Someone named Sammy has a
question about this, too.
Let's give her a call now.
(phone ringing)
- Hi Doug.
- Hey, Sammy.
- I have a question for you.
What is a black hole?
- That is a great question.
Well, I've gotta tell you,
this is one of the most
surprising questions in science
because a black hole sounds
like it might be a
simple thing to explain.
It's some kind of hole, right?
But the idea of a black hole
is one of the most advanced
and maybe one of the weirdest
ideas in all of science.
For starters, a black hole is
not actually a hole at all.
It's an object, a thing.
So, what kind of thing is a black hole?
Well at first it was just something
that scientists imagined could exist.
It was just an idea, a what-if.
So what's the idea of a black hole?
Well, you know how the
Earth has gravity, right?
We think of gravity as the invisible force
that keeps everything pulled down.
You can jump up and get
off the Earth's surface,
but only for a second or two.
Gravity pulls you back down.
It's not that we can't
escape the Earth's gravity.
You know we can send things to space,
but to do that we need to go really fast.
A rocket has to travel
at a speed of nearly 25,000 miles an hour
in order to get to outer space.
We call this escape speed.
Earth isn't the only thing
in space that has gravity.
Mars has gravity, the
Moon has gravity, too.
Now, because the moon is
smaller than the Earth
or less massive, it turns out the Moon
has less gravity than the Earth.
If you jump while standing on the Moon
you go a bit higher
before the Moon's gravity
pulls you all the way
back down to the surface.
This also means that
the Moon's escape speed
is much less than the Earth.
Rockets don't have to fly
as fast to escape the Moon.
The Moon's escape speed is
only about 5,000 miles an hour.
OK, that's the moon though.
What about an object more
massive than the Earth?
If you could stand on a
planet bigger than Earth,
the gravity would be stronger.
You wouldn't be able to jump
as high as you can on Earth.
And the escape speed would be even more
than the Earth's escape speed.
This is where the idea
of a black hole comes in.
Scientists asked themselves,
what if there were an object
so massive, an object that
had such strong gravity
that not even the fastest
thing in the universe
would have enough speed to escape it?
Let's think about what this might be like.
What even is the fastest
thing in the universe?
Before I say anything
more, try to take a guess.
Now would be a good time to
pause the video and discuss.
OK, you ready?
The fastest known thing
in the universe is light.
Maybe not too surprising, right?
When you turn on a light switch,
the time it takes for light
to go from the light bulb
to your eyes seems like
it happens instantly.
What if there were an object
with such strong gravity
that its escape speed was even higher
than the speed of light?
Would that mean even light
itself wouldn't be fast enough
to escape this object?
If you think about it, you
can start to imagine why
the name black hole makes a
pretty good name for this idea.
It would be like a hole
because an object like this
would have such strong gravity
anything that got anywhere near it
would get sucked in towards it.
A passing spaceship, nearby
planets, entire stars,
maybe even light itself.
If light couldn't escape
an object like this,
think of just how weird that would be.
Imagine if you could stand on
this object with a flashlight.
You go to point the flashlight
up to shine it into space,
but the gravity of the
object would be so strong
that the light wouldn't
even be able to go up.
It would bend back and fall
toward the ground beneath you.
So the object itself
would have to look black.
It would suck in any
light that got near it.
Now like I said, at first all of this
was just an idea, a what-if.
If such a thing existed, would
it really do that to light?
Can light really be bent?
But around the middle of the 1900s
scientists discovered
some reasons for thinking
that black holes might
actually exist in real life.
They started looking for
them using telescopes.
But as you might expect,
one reason why it'd be hard
to see a black hole is
because they're black,
and so is outer space,
but it should be possible,
especially if there's a black
hole sucking in material
from some nearby object like a star.
Maybe we'd see a bunch of
light getting sucked in
to a kind of black spot and disappearing.
Using telescopes, scientists
started finding places in the universe
where they think some
black holes might exist.
None of these places are anywhere near us,
which is good news.
We wouldn't want to get pulled into one.
But this is also the main reason
why it's been so hard to
actually get a photograph of one.
Even though a black hole
is a massive object,
they're all so far away from
us that scientists realized
we would need a telescope
the size of the Earth itself
just to be able to see one.
That is what's most amazing about this,
the first ever actual
image of a black hole.
A team of 200 astronomers worked together
all around the globe and used
eight different telescopes
to basically act like one
giant Earth-sized telescope.
It was not an easy thing to do.
Not only did the telescopes
all have to point
at the exact same place in space,
but to combine the view
from each telescope
involved really advanced computer skills
used by scientists like Katie Bouman.
Now we have photographic proof.
Black holes aren't just an
idea, they're a real thing.
What other kinds of strange things
will we be able to discover
by combining telescopes like this?
Will we be able to actually
see other planets like Earth
going around faraway stars?
Will we be able to find other things
we've only imagined could be
real in movies and stories?
Things like wormholes,
passageways that take us
to other parts of the galaxy.
One thing's for sure, it's
an exciting time to be alive.
That's all for this week's question.
Thanks Sammy for asking it.
Now for the next episode,
we're gonna do something
a little different again.
We're working on a hand-on activity
you can do for springtime.
I picked out three questions
from my question jar
that I'm thinking about answering.
When this video's done playing
you'll get to vote on one.
You can choose from,
are all baby birds born in the spring?
Why does it rain in the spring?
Or, how do flowers bloom in the spring?
So submit your vote when the video's over.
I wanna hear from all of you watching.
There are mysteries all around us.
Stay curious, and see you next week.
