A new theory suggests the mysterious, hypothetical "Planet 9" might not be a planet at all.
"Could a black hole explain the gravitational effects we are seeing in the outer solar system? A primordial black hole would have a very different signature, say Scholtz and Unwin. The hidden planet in our solar system could be a primordial black hole.

Primordial black holes (PBHs) are objects that formed just fractions of a second after the Big Bang, considered by many researchers among the … Mike Brown says. They hypothesize that it would be surrounded by a halo of … Primordial Black Holes and Space Hamburgers. There wouldn't be any way to tell the effects of a planet's gravity from that of a primordial black hole of the same mass.



Absolutely!"

While this is an interesting avenue of study, replacing a hypothetical planet with a hypothetical type of black hole may be overcomplicating the mystery of Planet Nine. Primordial black holes aren't formed from the collapse of a dead star (the more commonly-known mechanism for black hole formation that takes place relatively late in the universe's history).