One hell of a bang, and a massive release of energy, and then you would be left with a larger black hole. The more they are spinning the bigger the energy release. One article I read said that if the black holes were both the same size and spinning very fast indeed, then up to half the combined mass could be released as energy. Bow that is a bang to take notice of!

I just found this article recently. Coincidence? LOL http://www.csmonitor.com/2002/1120/p01s02-ussc.html

http://curious.astro.cornell.edu/question.php?number=327 If two bodies (stars, black holes, anything) get close enough to be gravitationally bound they will develop some sort of orbit in which the two bodies circle each other. Einstein's theory of General Relativity predicts that when two very massive objects(like Black Holes and Neutron Stars) are caught in an orbit like this they will generate Gravitational Waves (Ripples in Space-time). These Gravitational Waves carry energy away from the orbiting bodies which means that with each successive revolution they get closer to each other. Eventually the orbit gets so small that the two bodies merge. The merger of two black holes entails a lot of complicated General Relativity and some non-intuitive physics, but theorists use large supercomputers to simulate such events. There are two primary results to these mergers of which we can be sure of: 1. A single, more massive black hole 2. An extremely powerful burst of gravitational waves There are currently projects like LIGO which will attempt to directly detect the disturbances in space time caused by gravitational waves. They primarily expect to "see" the results of neutron star and black hole binary mergers. There was also a recent discovery of a black hole merger in a distant galaxy though this was discovered by observing the jet streams caused by the black holes. You should note that those results are still preliminary and unconfirmed.

All hell would break loose!

Lesbian sex!

Don't you learn it from school, that will be one big black hole 1+1 = 1 XD

They'd merge together or, if both large enough, would explode half way through the merging process. Though for that to happen is improbable as for them to be close enough to have a gravitational pull on eachother means that any matter that comes their way would get sucked in by the closest blackhole and increase the size of one of them

They don't move so how could they run into each other?

are you trying to pointe towards the LHC?

They would simply merge into one larger black hole.  

They will explode into a lame sci-fi channel show that will be canceled within a year.

1) "The ripples in space-time created when two black holes merge have been modelled to unprecedented accuracy, according to Einstein's equations, by a powerful new computer simulation. The "waveform" signatures produced in the simulation should help researchers identify the ripples in the data from gravitational wave detectors. Powerful gravitational waves are thought to shake the fabric of space-time when two black holes spiral towards each other and eventually merge. The waves have not yet been observed, but researchers have been trying to simulate the process on computers in order to predict the expected signal. That will help the nascent searches now in progress. The signals, called "waveforms", are shaped by factors such as the frequency at which the two black holes orbit each other, their relative masses and their spins. But modelling the merger has proven exceptionally difficult because the process is governed by Einstein's theory of general relativity." "The simulation followed two non-spinning black holes of equal mass that orbited each other between 1.5 and 4.5 times before merging. For black holes about 500,000 times the mass of the Sun, this final death spiral is expected to take just an hour or so, but the simulations required several days of computation time by 2000 individual processors at NASA's Columbia supercomputer in California, US. View an mpeg video of the simulation here." Source and further information: http://www.newscientist.com/article/dn9012-black-holes-collide-in-the-best-simulation-yet.html http://www.nasa.gov/centers/goddard/mpg/146898main_viz_shiftingall_21.320x240.mpg Further information: http://www.newscientist.com/blog/space/2007/05/battle-of-black-holes.html "In 2 billion years when our galaxy runs into Andromeda, the huge black hole that results may go walkabout." http://www.youtube.com/watch?v=C8jyHiLV4Zk Also here: http://www.youtube.com/watch?v=GAwO1okR074 2) Further information: - "A Nice Black Hole Merger Simulation": http://www.sciencebits.com/BlackHoleSimulation - "When Black Holes Merge": http://www.space.com/scienceastronomy/astronomy/blackhole_merges_020208.html - "Pair of Supermassive Black Holes Inhabit Same Galaxy, Destined to Collide": http://www.space.com/scienceastronomy/merging_backhole_021119.html - "Black Hole Merger": http://www.aip.org/png/2006/256.htm http://www.aip.org/mgr/png/images/bhmergermovie.mpg