Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site ucbvax.ARPA Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!ucbmiro!rimey From: rimey@ucbmiro.ARPA (Ken Rimey) Newsgroups: net.physics Subject: Re: YAQ about BLACK HOLES Message-ID: <10085@ucbvax.ARPA> Date: Thu, 22-Aug-85 04:55:17 EDT Article-I.D.: ucbvax.10085 Posted: Thu Aug 22 04:55:17 1985 Date-Received: Sat, 24-Aug-85 14:46:10 EDT References: <498@sri-arpa.ARPA> <349@eneevax.UUCP> Sender: usenet@ucbvax.ARPA Reply-To: rimey@ucbmiro.UUCP (Ken rimey) Organization: U.C. Berkeley Lines: 24 Todd Aven asks, >Can a black hole collide with another black hole in a finite >length of time in > a) its reference frame or > b) in an inertial reference frame outside the pair? The easy case to consider is that where one of the black holes is much smaller than the other. Then the smaller one will not perturb the larger one, and it will follow the same trajectory any small particle would follow. It will cross the Schwarzschild radius and hit the central singularity in a finite time as measured by someone riding on the particle. Of course, in speaking of a rider on the particle I am presuming that it is not a black hole. It is not clear what would be meant by the "reference frame" of a black hole. Question (b) makes sense in the general case. Everyone is taught the answer for the case of a black hole and a small test particle (which might as well be a black hole): The small particle never reaches the Schwarzschild radius. But what happens if instead of a small test particle we use a black hole comparable in size to the other black hole? I don't know. Do any of you people? Ken Rimey rimey@dali.berkeley.edu