> We shouldn't be able to see tides caused by changes on the mass distribution inside the horizon. ... if we hold the horizon fixed. If we don't let the horiz

> We shouldn't be able to see tides caused by changes on the mass distribution inside the horizon. ... if we hold the horizon fixed. If we don't let the horizons move at all we get all sorts of useful results like Hawking radiation via linear analysis. But if we let apparent horizons evolve dynamically taking into account anisotropic radiation reaction, the backreaction on the metric of the accretion of mass and angular momentum, and so forth, the full nonlinear theory becomes so complicated that I think it is fair to say that it is not in general well understood. We do know (empirically) that merged black holes ring down, which involves values sloshing about in the Weyl tidal tensor (in the 3+1 formalism). I am not certain treating the apparent horizon as a substance that settles down (emitting gravitational radiation) is conceptually useful, as opposed to the dynamical apparent horizon being generated by the movement of whatever's inside the merged binary plus most of the outgoing waves falling back towards the merged binary. The paper press-released at the top is not about merger and ringdown, though, so the internal configuration of the Kerr BH is irrelevant. Also, Lense-Thirring torques, the topic of the paper, arise even in non-BH Kerr spacetimes. We even see them in Earth orbit, and in due course probably will have good data from solar orbits too. >>> Does frame dragging originate at the event horizon > That "originates" word is funny I think it would be enlightening if you were to expand on that.