Gravititational potential energy can be released quite quickly during the collision, and it is a very efficient process. Peak output would occur over a brief time period, too, so there would not be a sustained period when tremendous energies are being released.<br /><br /><br />I would assume most (all?) black holes in the universe are still growing (the mini ones still remain theoretical) and will continue to grow for a very long time. The universe will have to expand considerably to get the density of matter low enough for the black holes to finally stop ingesting. Additionally, as Hawking has pointed out, black holes have a characteristic temperature, inversely proportional to their mass. (the really big ones are colder). As long as a black hole is colder than the cosmic background radiation, they will still absorb that, even if totally deprived of matter. Once the CBR dissipates enough that black holes become warmer in comparison, the black holes will start to evaporate. This process takes a <i><b>very</b></i> long time.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>