Two black holes orbit around each other and generate space-time ripples called gravitational waves in this animation. As the black holes get closer, the waves increase in frequency. Eventually, the event horizons merge into a peanut-shaped object, generating one very high-frequency wave. Within a rotation, the black holes merge completely. One lower-frequency wave, called the ring down, ripples out after the merger.
Credit: NASA's Goddard Space Flight Center Conceptual Image Lab