and violent objects in the universe.

They can warp space and time

and rip entire stars to pieces.

So, what if I told you that astrophysicists

think there's one lurking in our very own solar system?

Reporter: Then a new discovery

rocked the astronomical world to its foundation.

Narrator: Now, before you freak out,

you should know that our planet isn't about

to get sucked up and reappear in another galaxy.

If there is a black hole,

it's at least 20 times farther from Earth

than the furthest planet, Neptune,

in a distant region of our solar system

called the extended Kuiper Belt.

The belt is home to billions of icy objects,

like comets and asteroids.

And in 2016, astronomers Konstantin Batygin

and Mike Brown noticed that some of them

have highly unusual orbits.

While most objects in our solar system

orbit the same plane, and in the same direction,

the orbit of these objects looks like this.

Some of them orbit on a slight tilt.

Others orbit backwards.

And still others orbit perpendicular

to the plane of our solar system.

Konstantin Batygin: Imagine the plane of the solar system

as being your table.

These orbits are stacked like books.

Narrator: They concluded that this could mean

only one thing.

Batygin: In order to generate this population

of highly inclined, perpendicular orbits,

you need some distant gravitational pull.

Narrator: By their calculation, that gravitational pull

is five times greater than Earth's.

So they reasoned that this "something"

was as large as a planet orbiting our sun.

In fact, they even went so far to give it a name,

Planet 9.

Now, of course, if they were to confirm this discovery,

it would be groundbreaking.

The first new planet in our solar system

since the discovery of Neptune in 1846.

Reporter: Very little is known about Neptune,

the last of the giants on this tour.

Narrator: But there was a problem.

No one was able to observe the planet directly.

Now, that could be because finding a planet that far away

is like searching for a needle in a haystack...

with the lights off

and only a vague idea of where the haystack even is.

Or it could be because, well,

that "something" is not a planet at all.

In a study published in the fall of 2019,

theoretical physicists Jakub Scholtz and James Unwin

proposed it could actually be a black hole.

Not just any black hole, but a primordial black hole.

Jakub Scholtz: Primordial black hole is a remnant

from the Big Bang that came from a very dense region

that almost instantly collapsed into a small black hole

right during the birth of the universe.

Narrator: And they do mean small.

About the size of a tennis ball.

That's right; this black hole

would fit in the palm of your hands.

While the idea might sound far-fetched,

it isn't totally out there.

For over 50 years, astronomers have proposed the universe

is littered with primordial black holes.

And we've even observed fluctuations of starlight

in our own galaxy,

which primordial black holes could explain.

Not only that, but Scholtz and Unwin also noticed

that if a primordial black hole orbited the sun,

it would have the same effect on objects in the Kuiper Belt

as a large planet.

But whether it's a black hole or a planet,

there's another mystery.

Where did it come from?

One idea is that the object was wandering through the galaxy

and got caught in the sun's gravity,

but for now, this is all just speculation.

James Unwin: If we do do our searches and it turns out

that there is a planet in the outer solar system,

this would be an absolutely incredible discovery.

Such a strange planet on such an odd orbit.

It would really change our understanding

of the history of the solar system.

Narrator: But if it is proven that this is a black hole

in our own outer solar system?

Unwin: This is completely mind-blowing.

And the fact that this not only would change

our understanding of solar system physics,

but it also gives us a new window into astrophysics,

into early-universe cosmology,

and into, potentially into, the fundamentals

of particle physics.

Narrator: Whether it's a planet, a black hole,

or something else entirely,

one thing is for sure:

When we do find the source

of this mysterious gravitational pull, it will be huge.