For astronomers it’s clear that galaxies get bigger through galactic mergers. But they have always wondered what happens with the supermassive black holes that seem to always lurk at the heart of galaxies. What happens when two compact objects with millions of times the mass of our sun collide? An international team of physicists has developed a computer simulation designed to answer this question. It turns out that the interaction depends a lot on the amount of hot gas surrounding each black hole. As the black holes start to interact, this gas exerts a frictional force on the black holes, slowing down their spin rate. Once they get within the width of our solar system, they start emitting gravitational waves, which continues to extract energy from the system. This causes them to continue coming together, and eventually merge. These mergers should be so energetic, they’ll generate gravitational waves detectable across space.

http://news.stanford.edu/pr/2007/pr-hole-061307.html

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