[Phoenix-D]

You can't see a black hole, more or less by definiton. What you -can- do is predict what it would do, and look for those. By that standard we have found quite a few. (or something that behaves the same way).

In case you're inclined to dismiss it on that basis- keep in mind that's how we know about the existence of the electron and the atom, not to mention a load of other stuff.