[AnimalMuppet]

> We don't really know what's inside the event horizon or how the mass if actually distributed.

Is that entirely true? We can tell if the black hole is rotating because of the frame dragging that happens outside the event horizon. Could we tell anything about the radial distribution of mass from the shape of space outside the event horizon? (I'm asking; I don't know enough GR to know.)

[mytailorisrich]

Well we do reasonably know that the mass must be very densely packed at the centre but we do not know exactly how, we do not know if there is a singularity or not.

[AnimalMuppet]

If a rotating black hole was not just a point, if it had a radial distribution, would the frame dragging be different? Could we tell that way?