50 years ago this summer, astronomers Russell Hulse and Joseph Taylor went pulsar hunting. And they bagged a real trophy – a binary system that contained a pulsar and another dead star. The discovery, and their later analysis of the system, earned Hulse and Taylor the 1993 Nobel Prize in Physics.

Both members of the binary are neutron stars – the crushed cores of once-mighty stars. Each is about 1.4 times the mass of the Sun, but only about as big as Earth. One of the stars rotates rapidly, sending out “pulses” of energy at each turn like a cosmic lighthouse. That makes the star a pulsar.

It spins about 17 times per second. But the timing changes ever so slightly as the stars orbit each other. The changes have revealed that the stars are spiraling closer together – by about three millimeters per orbit.

The stars are getting closer because they’re losing energy – by producing ripples in space and time known as gravitational waves. They were predicted by Albert Einstein’s theory of gravity. But the binary star system provided the first evidence that the waves actually exist.

The two stars should slam together in a few hundred million years, producing a torrent of gravitational waves. In August of 2017, in fact, a gravitational-wave observatory “heard” the merger of another pair of neutron stars – more confirmation that Einstein’s theory of gravity was right.

Script by Damond Benningfield