We just have obtained the first "picture" of a black hole, the supermassive blackhole at the center of galaxy M87. As spelled in this approved answer, there were multiple unsolved questions to be answered. Based on this picture, can we already confirm any of these? If not, what we will need?
I repeat the questions from the linked answer for simplicity:
These observations would answer some practical questions about the black holes that have long intrigued us, questions like:
1) it will be that the black hole has the correct size as predicted by the Theory of General Relativity.
2) it will be that the event horizon (the boundary of the black hole) is circular (as predicted) or, in contrast, is oblong (stretched).
3) it will be that the radio broadcasts extend more than you think.
4) it will be that there is some other deviation from the expected behavior.