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How did observations of the binary pulsar PSR 1913+16 support the existence of gravitational waves?

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gravitational lens — gravity A galactic cluster, about five billion light-years away, produces a tremendous gravitational field that “bends” light around it. This lens produces multiple copies of a blue galaxy about twice as distant. Four images are visible in a circle surrounding the lens; a fifth is visible near the center of the picture, which was taken by the Hubble Space Telescope.

Observations of the binary pulsar PSR 1913+16 provided the first experimental evidence for the existence of gravitational waves, supporting Albert Einstein’s general theory of relativity.12

Discovered in 1974 by Russell Hulse and Joseph Taylor, Jr., the system consists of two neutron stars in a tight orbit. According to general relativity, such a system should emit gravitational waves, causing the stars to lose orbital energy and spiral closer together.12

By precisely timing the pulsar's radio emissions over several years, researchers observed a gradual decrease in the orbital period—approximately 75 millionths of a second per year—that matched the predictions of general relativity to within 0.5 percent accuracy. Because gravitational radiation is the only known physical mechanism that could account for this energy loss and the resulting orbital decay, these observations offered compelling indirect proof of gravitational waves long before their direct detection by LIGO in 2015.123