The thing about black holes is that they are very dense.  If we took the entire 2,000,000,000,000,000,000,000,000,000,000 Kg of the Sun (This is the real mass of the Sun) and turned it into a black hole, it would be about 6 Km in diameter. It is theorized that there are around 100 Million Black holes in the Milky Way Galaxy alone.  But if they aren’t near a large reservoir of gas and dust, with their small size they are pretty harmless and invisible.  The only way we could find them would be through their gravitational influence, which is hard to...