Yes, I am aware of observations of "massive objects", for example near the center of the galaxy. But is there any evidence that the object in question is a black hole, with all its commonly attributed properties? Or are black holes just an unconfirmed artifact of general relativity, i.e. something that is an abstract mathematical concept and not a real object?
EDIT: That is not an answer to my question. I did not ask about means of detecting them, I am aware of those means. I'm interested if there's anything suggesting that the properties commonly attributed to black holes, other than large mass, have anything to do with reality, or are completely abstract and deduced from math.
