© Wikimedia Commons, Public Domain. Author: M. Haynes et Lorimer, 2001.
The binary system PSR 1913+15 consists of a pulsar and another neutron star orbiting one another. If gravitational waves are emitted by this binary star system, the orbit should "decay," with each orbit taking a little bit longer to complete. Astronomers have monitored the system since 1974, using the timing of radio waves from the pulsar to infer the orbital period. The time between successive periastra (the position in the elliptical orbit when the two stars are closest together) has increased by 40 seconds over the last 30 years. This orbital decay rate is in excellent agreement with the predictions of general relativity (solid curve) for gravitational wave emission. (Unit: 3)