Astronomers have long speculated about the existence of "Planet 9," a super-Earth-sizedin the outer regions of our solar system. It's been hypothesized as an explanation for the unusual clustering of and comet orbits out beyond Neptune.
The planet, if it did exist, would most likely be five times the size of Earth and orbit the sun at 250 times the distance. Being so far away, we haven't been able to catch a glimpse of it yet.
The mysterious, hidden planet is, of course, just a hypothesis at this point, and there have been other explanations for the strange paths taken by objects like asteroids. Now there's a new theory: a. A primordial black hole, to be more precise.
Primordial black holes are hypothetical black holes that originated soon after the Big Bang. Compared to other black holes, a PBH is old and small. Their existence has been difficult to prove -- as authors James Unwin and Jakub Scholtz speculated to Gizmodo, this primordial black hole could be the size of a bowling ball. Weirdly enough, the black hole is small enough for Unwin and Scholtz to include a 1:1 diagram of it in their paper, released on preprint website arXiv.
At that size though, it may be impossible to spot. Can you imagine trying to spot completely black bowling ball on the other side of the solar system? Me neither.
Regardless, the new paper suggests the strange orbits in the outer regions of our solar system could be the result of one of these primordial black holes.
A bowling ball-sized black hole of the outer reaches of the solar system is an outlandish theory, but at this point it's no less plausible than the existence of super Earth-sized planet. Both scenarios would be equally exciting for astronomers.