CAPE CANAVERAL, Fla. - With just hours left in the countdown, NASA (news - web sites) called off the launch Wednesday of a spacecraft that will hunt for emerging black holes. The launch was postponed for at least a day because of trouble with an electronic box aboard the unmanned Delta rocket, part of the safety system for destroying the vehicle if it flies off course. Once in orbit, NASA's Swift spacecraft will swivel quickly to detect gamma ray bursts in the universe, which scientists believe represent the creation of black holes. Black holes are believed to be the invisible...