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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.

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closed as too broad by Kyle Kanos, Feynmans Out for Grumpy Cat, Gert, Jon Custer, John Rennie Apr 13 at 9:50

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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Yes, the black hole is the right size. Or at least the size of the photon shadow yields a mass that agrees with the mass inferred by stellar dynamics in M87.

Yes, the shadow is very circular (to better than 10%), as predicted by GR.

Reference: Akiyama et al. and the Event Horizon Telescope collaboration (2019).

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