Objects orbiting under the influence of their own gravity are another important source of gravitational waves. For the waves to be strong enough to be detectable here on Earth, the ideal sources are very copact objects, such as black holes, orbiting at high speed. Such systems lose substantial amounts of energy by radiating gravitational waves; in consequence, the orbit shrinks and the orbital speed of the two objects increases. In the end, the two objects must collide and merge. The images above show a computer simulation of gravitational waves that are generated after the merger of two black holes.