> A tennis ball mass black hole going close to the speed of light would go right through the Earth without too much fuss. The black hole's radius would be too small (smaller than an electron) to cause any damage.
How would such black holes exist in the first place? I thought black holes are formed if the mass of the star is at least 3 times the mass of our Sun.
Primordial black holes are another possible way (besides star collapse) that BHs could form.
The theory is that during the immediate aftermath of the Big Bang, the distribution of mass-energy became chaotic, with local hotspots where mass-energy was more dense, and other spots where it was less dense.
GR says that if ANY amount of mass-energy comes to occupy a small enough area, then that is a black hole. Star collapse BHs have a lower mass limit because their own gravity is what forces their mass into a region small enough to become a BH.
So primordial BHs could have formed with arbitrarily small mass, because they didn't have to rely on their own gravity to attain BH density. The Big Bang did it, for them.
Any primordial black holes of low mass that may have formed would have evaporated long ago through Hawking radiation. If you plug the mass of a tennis ball into the equations, it would evaporate in well under a second. (Btw, don't stand next to anything that radiates the entire mass-energy of a tennis ball in under a second. Small black holes shine really brightly)
How would such black holes exist in the first place? I thought black holes are formed if the mass of the star is at least 3 times the mass of our Sun.