LISA will be able to detect the most powerful outflows of energy in the Universe, generated when two massive black holes orbit, collide, and merge. These mergers will produce gravitational waves, sometimes called "ripples in space-time." Additionally, LISA will test Einstein's prediction——that gravitational waves and light waves should travel at the same speed——by comparing the arrival times of light and gravitational waves emitted by a source.

Artist's concept of gravitational wave action.