Primordial Black Holes

One leading candidate for dark matter is so-called ‘primordial black holes’ which are the smallest kind of black holes, which might or might not exist. They may have formed just after the big bang. They may be as small as a proton and could have virtually any mass, from the mass of small asteroids up to thousands of solar masses. Small black holes with the mass of small asteroids would be so abundant that they’d strike the earth fairly frequently, probably as frequently as asteroids. Their Schwarzschild radii would be literally atomic, so they wouldn’t really ‘eat’ much when they encounter the earth, and they’d end up passing straight through. It has even been suggested that the Tunguska event was a black hole, superheating the gas around it with its intense gravity as it punched through the atmosphere. A 2019 paper even suggested that the hypothetical 9th planet in our solar system might be a primordial black hole the size of a tennis ball. Its gravitational effects could explain the peculiar clustering of orbits for a group of extreme trans-Neptunian objects.