Black Hole Pair Sets Proximity Record - Yahoo! News: "Scientists think that when black holes collide, they generate enormous amounts of energy—more than all the stars in the universe combined according to one recent model—and send out gravitational waves rippling through space-time in every direction.
Such gravitational waves could be detected with the ground based Laser Interferometer Gravitational-Wave Observatory (LIGO) or the proposed Laser Interferometer Space Antenna (LISA) space mission."