Jillian's Guide to Black Holes: Forming - Types - Outside - Inside - Finding - References - Websites
If we can't see it, then we can't find out anything about 'em?
Psssh! It may be black, but it's not completely hidden! We can tell the size of the event horizon (the black hole's "mass"), whether it's charged or not, and whether it's spinning and at what rate. Remember that a star can collapse to form a black hole? All information about what the star is made of is lost. The star could have been made of antimatter or matter, and it wouldn't make a difference in the resulting black hole. We can't peer past the event horizon to see the singularity...even if we could, the singularity is a damn strange place. If the collapsing star were not quite spherical, those deviations were burned off during the collapse, so all black holes have the same general shape. What differs from hole to hole is the mass, charge, and angular velocity.
Three types of black holes
What's with the green circle, blue square, black diamond stuff?