Stingray mentioned this in an earlier post---he is at Penn State where Ashtekar is and goes to talks. Ashtekar has put the study of black holes on a new track, using a new kind of system of horizons.(adsbygoogle = window.adsbygoogle || []).push({});

Instead of the old notion of Event Horizon which is awkward to use because requires looking infinitely far into the future-----that is, the EH is not operationally defined----instead of EH he and his co-workers say use

dynamical and isolated horizons.

I've seen smaller papers by Ashtekar about this (e.g. "How do black holes grow?") over the past two or three years. Now the big paper is out

----exerpt from http://arxiv.org/gr-qc/0407042 [Broken] ------

" Global nature of event horizons.

An event horizon is defined as the future boundary of the causal past of future null infinity. While this definition neatly encodes the idea that an outside observer can not ‘look in to’ a black hole, it is too global for many applications. First, since it refers to null infinity, it can not be used in spatially compact space-times. Surely, one should be able to analyze black hole dynamics also in these space-times. More importantly, the notion is teleological; it lets us speak of a black hole only after we have constructed the entire space-time. Thus, for example, an event horizon may well be developing in the room you are now sitting in anticipation of a gravitational collapse that may occur in this region of our galaxy a million years from now. When astrophysicists say that they have discovered a black hole in the center of our galaxy, they are referring to something much more concrete and quasi-local than an event horizon. Is there a satisfactory notion that captures what they are referring to? ..."

and indeed Ashtekar and Badri Krishnan have a satisfactory answer to that question

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# Ashtekar's big one restructures Black Hole study

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