Are there any black holes made of antimatter?

Question

And what would happen if an antimatter black hole and a matter black hole would collide?

Answer 1

According to theory, a black hole resulting from the collapse of antimatter is indistinguishable from one resulting from the collapse of matter. If a difference were found, that would invalidate the theory, but we don't know what difference to look for.

There is very little antimatter in the universe, and it isn't observed in concentrations that could collapse to form black holes. Such concentrations should be very conspicuous, so we don't believe they exist. We thus believe that the histories of black holes that we observe involve matter, not antimatter.

If a black hole whose history involves antimatter collides with one whose history involves matter, the theory says that nothing special should happen: it's just like any other black hole collision.