In a paper by Ashtekar et al in 2013 on the approach to the final state to a stationary black hole they study the evolution of the multipole moments of dynamical horizons, which relax away (except for mono and dipole moments) to a stationary horizon and merges with the event horizon. They state that this is due to mass and gravitational waves entering the horizon from outside the event horizon. They speculate that those gravitational waves arise and may have some correlation to others that radiate to infinity from outside the horizons that we'd see during the final stage of black hole formation or mergers of two black holes (e.g. the merger and ring down phases). Dynamical horizons are similar to apparent horizons but they argue theirs is a covariant description (apparent horizons depend on the foliation used). They mention that possibly the grav waves we see at infinity may tell us something about the multipole moments of the dynamical horizon, in a completely non quantum description. It seems this would mean that information is extracted from the black hole.

  • $\begingroup$ Thanks for the edit. I've not figured out how to enter links yet. $\endgroup$ – Bob Bee Apr 10 '16 at 7:17
  • $\begingroup$ Can you clarify what you are asking? Is the last sentence your real question? Why should there be a problem getting information from a dynamic horizon? It's only a true horizon that is an absolute boundary. $\endgroup$ – John Rennie Apr 10 '16 at 7:18
  • $\begingroup$ My understanding is that dynamic horizons only arise inside real event horizons, which don't become obvious till later when the full spacetime can be 'seen'. My wording may not be perfect. Ashtekar states that the radiation comes from outside, they clearly can not come from inside. My question was that if indeed the grav waves at infinity are in any way correlated with the grav waves that fall in, it looks like we could get information about what made the horizon relax to Kerr. Admittedly, that is not clear is information from the horizon, which belongs to the black hole and would $\endgroup$ – Bob Bee Apr 11 '16 at 1:11
  • $\begingroup$ Continued - conceivably represent t black hole information. I know, a few uncertain statements. $\endgroup$ – Bob Bee Apr 11 '16 at 1:18

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