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The Question
(Submitted July 11, 2001)
What would happen if two Black Holes merged? Would superpositioning of the
gravitational fields make the event horizon radii shrink?
The Answer
The size of the event horizon is determined solely by the mass and
spin (if it happens to be spinning) of the black hole. If two were to
orbit each other (or any two massive bodies such as neutron stars) a
lot of energy in the form of gravity waves would be emitted. This will
leak energy out of the system, until the two objects merge. It would
appear that the smaller one was swallowed by the larger, but it really
is a merger around their common center of mass, and the event horizon
would grow according to the new higher mass.
Also there is more information on this at:
http://www.astronomical.org/astbook/blkhole.html
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/BlackHoleAnat.html
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GravWaves.html
http://lisa.jpl.nasa.gov/SCIENCE/mbh.html
Two experiments which hope to detect and confirm this can be seen at:
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/LIGO.html
http://lisa.jpl.nasa.gov/
And a simulation of such an event can be found at:
http://jean-luc.aei-potsdam.mpg.de/Press/BH1999/
Hope this helps,
Michael Arida for Ask a High Energy Astronomer
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