Pulsar pair ripples spacetime

Duo’s tightening orbits provide even stronger evidence for gravitational waves

PULSAR PAIR  A system of two radio beam–emitting pulsars locked in tight orbits, illustrated here, is an ideal test bed for measuring gravitational waves and other effects of general relativity. 

© MPIfR, M. Kramer

GENEVA — A dancing duo of cosmic beacons has provided scientists with the most precise measurement, albeit an indirect one, of ripples in spacetime called gravitational waves.

The measurement comes from analyzing the only known pair of gravitationally bound pulsars, dense cores of dead stars that emit intense beams of radio waves with the regularity of a nearly perfect clock. Michael Kramer, an astrophysicist at the Max Planck Institute for Radio Astronomy in Bonn, Germany, and colleagues precisely tracked the deterioration of the pulsars’ orbits, presumably due to loss of energy in the form of gravitational waves. The rate of orbital wane matches perfectly with the predictions of general relativity, Kramer reported December 16 at the Texas Symposium on Relativistic Astrophysics.

The double pulsar system J0737-3039, discovered in 2003, is an astrophysicist’s dream. By analyzing the radio beams, researchers can probe the wild things that happen when the small but massive celestial objects circle each other at roughly a million kilometers an hour. Under the rules of general relativity, the pulsars should plow through spacetime and generate ripples that carry away energy, leading the pulsars to gradually fall toward each other.

Using observations from several telescopes over more than a decade, Kramer and his team determined that the pulsars are approaching each other by 7.152 millimeters a day, give or take a micrometer. That’s exactly what theory predicts based on the mass and acceleration of the pulsars.

Though gravitational waves have yet to be detected by observatories on Earth (SN: 10/17/15, p. 24), Kramer’s work adds to the haul of evidence supporting the waves’ existence. The 1993 Nobel Prize went to a pair of physicists who used a binary system with one pulsar to calculate gravitational wave emission.

Editor’s Note: This story was updated Jan. 6, 2016, to correct the name of the pulsar system.

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