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Natural Science Forum / Physics / Research / August 2007Q: Black Hole Horizon
25-AUG-2007 Hi all - Assuming, for the sake of simplicity, a non-rotating BH, it's been conjectured that for an external observer the "image" of any matter falling through the critical circumference is (forever) frozen at the horizon. Two questions: 1. Doesn't this essentially preserve (some) information about the infalling matter, for any external observer, and 2. Doesn't this endow the BH with hair? The idea seems to suggest that any BH that has ingested matter would have a horizon forever postered with the images of these hapless bits, for any passing observer to see. How then would the black hole remain dark to the outside universe? cheers, mark jonathan horn Hi! > Assuming, for the sake of simplicity, a non-rotating BH, it's been > conjectured that for an external observer the "image" of any matter [quoted text clipped - 10 lines] > for any passing observer to see. How then would the black hole remain > dark to the outside universe? 1. No. Because there is no way to access such information (from outside the black hole). For instance if some sort of transmitter approaches BH horizon the signal intensity exponentially decays as that transmitter approaches horizon (See, for instance, problem (and solution) #15.10 in ``Problem Book in Relativity and Gravitation'' by Lightman et al.), the time constant in such an exponent is of order R_h/c. There is also no way to ``lit up'' the matter ``postered'' on the horizon because the ``light'' one could use to do that will not catch up with the such matter before it enters the horizon. 2. Various ``no-hair'' assertions for black holes do not prohibit the existence of such perturbations around black holes. But such perturbations either decay rapidly or are radiated away, leaving black hole itself without any ``hairs''. WBR,  SignatureB. |
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