In 2016, astrophysicists Konstantin Batygin and Mike Brown noticed unusual gravitational activity in the outer solar system.
They speculated this activity was from a ninth planet situated in the Kuiper belt.
But in late 2019, astrophysicists James Unwin and Jakub Scholtz propose Planet 9 isn't a planet but actually a primordial black hole.
If found, that would be a black hole the size of a tennis ball.
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.
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.