Pulsars are small and extremely dense stellar objects left behind after massive stars explode.

They spin at staggering speeds, generating huge gravity fields and emitting strong beams of radio waves from their magnetic poles, much as lighthouses emit beams of light, which can be picked up by radio-telescopes on Earth.

Scientists know of more than 1,700 pulsars in our galaxy but of only one binary-pulsar system, discovered in 2003. It comprises two pulsars locked into close orbit around each other, so close they could fit within the Sun.

Because of its strong gravitational field, this system is the best place to test Einstein’s 93-year-old theory, the international team of astrophysicists reported in the July 3 edition of the journal ‘science’.

“Einstein’s theory predicted that, in such a field, an object’s spin axis should slowly change direction as the pulsar orbits around its companion,” said Victoria Kaspi, Lorne Trottier Chair in Astrophysics and Cosmology at McGill University in Montreal, Canada.

“Imagine a spinning top when it’s slightly non-vertical, the spin axis slowly changes direction, an elegant motion called ‘precession’.”

Using the beams of radio waves to determine the pulsars’ movements, the researchers found that one of the two pulsars was indeed precessing, as Einstein predicted in 1915.