Re: How many identified Black Holes are there in the Universe?

It all depends on how strict your requirements are. There are two types of well-established black holes. The first type are black holes with a few times the mass of the sun. These are generally created by very massive stars when they go supernova. Astronomers have found several objects in our galaxy (the Milky Way) which seem to fit this description.

The other type are supermassive black holes at the centers of galaxies. The best example is at the center of the Milky Way, where astronomers have watched stars zoom very close to a very massive, very dark object. There is also good evidence that similar, even more massive black holes lie at the centers of other galaxies. Most astronomers believe that there's a supermassive black hole at the center of every big galaxy. If that's true, then there are as many supermassive black holes as there are galaxies, or somewhere between 1 and 10 billion in the observable universe. If you include all the stellar-mass black holes, there could be something like 10¹⁷ black holes in the observable universe. That's quite a lot, but it's smaller than the number of stars in the observable universe (10²⁰) and quite a bit smaller than the number of atoms in your body (10²⁸)!