Are primordial black holes common in the universe? It doesn't seem like it.
What would a universe flooded with primordial black holes look like? That's the million-dollar question, which we need to answer if we want to test this hypothesis.For one thing, the black holes may randomly crash into other things, gravitationally attract other things, and just generally cause mayhem. Kilogram-mass black holes hitting the Earth could trigger earthquakes. A silent black hole may pull apart binary pairs of stars or disrupt entire dwarf galaxies. A black hole ramming into a neutron star could ignite a terrible explosion. Even the hypothetical Planet Nine could be a black hole no bigger than a tennis ball. ...
Alas, despite all our attempts, we cannot reconcile the existence of primordial black holes with the universe that we see. For every possible observational avenue, the primordial black holes cause so much mayhem that it would be noticeable to us.
In other words, as difficult as it is to explain the masses of the merging black holes that LIGO witnessed, if you want a universe with those black holes to be primordial, it would be detectable in other ways.
Ok, may as well quote from the "Planet nine black hole" story also, even though Pluto is already planet #9. I guess the Space.com folks got confused and meant planet ten.
Over the past few years, researchers have noticed an odd clustering in the orbits of multiple trans-Neptunian objects (TNOs), which dwell in the dark depths of the far outer solar system. Some scientists have hypothesized that the TNOs' paths have been sculpted by the gravitational pull of a big object way out there, something five to 10 times more massive than Earth (though others think the TNOs may just be tugging on each other).This big "perturber," if it exists, may be a planet -- the so-called "Planet Nine," or "Planet X" or "Planet Next" for those who will always regard Pluto as the ninth planet. But there's another possibility as well: The shepherding object may be a black hole, one that crams all that mass into a sphere the size of a grapefruit.
I sure hope there's a tiny black hole in our solar system -- that's practically the only way we humans would ever have a chance to examine one up close.
