Hello to all ! I wanted to ask a question in this forum. I am french, and I have discussed this topic in a french physics forum, but with no clear conclusion. I hope I'll have another insights in this forum, which seems very well frequented. I know the underlying subject has been discussed in this forum already (with no clear conclusion either !) : can an infalling object in a black hole ever enter the horizon before the end of the universe, or before the BH evaporates ? But I'll try to formulate the problem in a new way, trying to avoid traditionnal pitfalls and shortcomings, and particulary without using the simultaneity concept (or the question WHEN the object enter the horizon ?), wich is very tricky in this context. Here is a mind experience and the question : Let a regular BH, generating a Schwartzschild metric. Let an observer O at fixed Schw. distance from the BH, in near Minkowski metric and time. The observer sees an infalling object passing near it at his Minkowski time T1 (radial free fall in the BH). Mass of object and observer is negligible compared to the mass of the BH. The object will disappear from the detecting instruments of O (which does not mean that the object have crossed the horizon) at observer/Minkowski time T2. When (at whatever moment) the object crosses the horizon, the horizon is disturbed, the BH "loose his hair" and emit gravitational waves. The observer O detects the gravitational waves at his time T3. The question is : what is this time T3 ? Here are some possible answers : Never (T3 = infinite) At some finite Minkowski time T3. In this case what is the formula which gives T3 ? The GW will not be detectable (for example infinitly expanded), or GW are detectable but with no clear signal at horizon cross, so this mind experience cannot give clue about horizon crossing (this answer is fundamentally different from answer 1). This mind experience has some flaw in his description or assumptions so there is no answer (please kindly explicit the flaws). GR is not sufficient to give the answer. We must take into account quantum or tunnel effects when matter reaches planck distance from the horizon. Some other answer ? My own answer is something like 3. But in this case, I wonder what is the exact signification of articles like http://kipac.stanford.edu/kipac/black-holes-eating-stars-and-making-waves (there are a lot of such articles). If the answer is 3, we can only detect matter approaching horizon, but we can never say that matter have crossed the horizon and have been "eated" by BH. The final question if the answer is 3 (or 1 BTW) is : what are the facts and measures, or mind experience, which can invalidate the "frozen star"model (Lifchits model for example) of BH, with matter infinitly approaching horizon but never crosses it in our referential ? Thanks in advance for your answers !