Question

To what extent are the astronomically observed black hole candidates compatible with GR black holes?

Answer 1

Do they all fit Schwarzschild black holes? How people compare them with more complicate BH solutions as spinning BH solutions (even if they are not known analytically), say.

I'd like more than qualitative comments, if possible.

Answer 2

Schwarzschild black holes are eternal black holes (BH that have existed for all time. No physical black hole satisfies this property. In fact, almost all astronomical black holes spin and hence are closer to Kerr black holes.