Joseph Taylor

Today is the birthday of Joseph H. Taylor Jr., born in Philadelphia in 1941. He grew up on his family’s farm in Cinnaminson Township, NJ, building ham-radio antennas with his brother. In high school he built a working radio telescope. By 1974 Taylor was a radio astronomer using the 300-meter Arecibo telescope in Puerto Rico. That’s when he and his graduate student Russell Hulse discovered a pulsar, a rapidly spinning core of a dead star that regularly emits an intense beam of radio waves. Pulsars had been found before, but this one was special because it was orbiting in tandem with another nearby massive stellar object. Two dense objects orbiting so closely (including one that regularly beams a detectable signal) are a great testbed for Einstein’s theory of general relativity. Taylor and Hulse found that, just as Einstein predicted, the two stars are orbiting each other faster and faster—the eight-hour orbital period decreases by about 75 millionths of a second each year. The energy lost as the orbits shrink is carried away by gravitational waves. As a result, the pulsar system provided the first evidence, albeit indirect, of the existence of the waves predicted by Einstein in 1916. Taylor and Hulse shared the 1993 Nobel Prize in Physics. Twenty-three years later, on Feb. 11, 2016, scientists with the LIGO experiment announced the first direct detection of gravitational waves. Although the discovery was a major achievement, it wasn’t a surprise because of the work done by Taylor and Hulse. (Photo credit: AIP Emilio Segrè Visual Archives, Physics Today Collection)

Date in History: 29 March 1941