Einstein's theory of general relativity has once again been vindicated by two pulsars locked in close binaries.
The timing of the pulsar pair's pulse can be measured, just as predicted and expected, after 16 years of observing them. This is the first time these effects have been observed.
The system of compact stars was studied to test gravity theories in the presence of strong gravitational fields.
We were able to test a cornerstone of Einstein's theory, the energy carried by gravitational waves, with a precision that is 25 times better than with the prize winning Hulse-Taylor pulsar, and 1,000 times better than currently possible with the detectors.
The most useful stars in the sky are s Pulsars. They are a type of star that is very small and dense, and can be up to 12 miles across.
The fact that they pulse is what makes them pulsars. They have beams of radiation shooting from their poles that flash like a lighthouse beam when the star rotates at up to millisecond speeds.
The flashes are incredibly timed, which means that they are the most useful stars in the Universe. Variations in their timing can be used for a variety of purposes.
The only double pulsar discovered to date, located around 2,400 light-years away, presented a new opportunity for study, and the researchers called it an "unrivalled laboratory" for testing gravity theories.
The two pulsars are very close together. One rotates at a rate of 44 times per second. The younger one rotates once every 2.8 seconds. The timing and angle of each other's pulse can be affected by the strong gravitational fields of these objects.
Over the course of 16 years, the researchers used seven powerful telescopes around the world.
"We follow the propagation of radio photons emitted from a Cosmic Lighthouse, a pulsar, and track their motion in the strong gravitational field of a companion pulsar," says astrophysicist Ingrid Stairs of the University of British Columbia in Canada.
The light is delayed due to a strong curvature of spacetime around the companion, but also that the light is diverted by a small angle of 0.04 degrees that we can detect. This is the first time that an experiment has been conducted at such a high spacetime curve.
The researchers performed seven tests of general relativity, including the way the orientation of the binaries's orbit changes, known as apsidal precession, and the way the pulsars drag space-time around with them as they spin. This allowed for accurate tracking of the timing.
"Our precision allows us to measure the effect of time dilation that makes clocks run slower in gravitational fields, which is one of the reasons why we study the phenomenon," says Dick Manchester from the CSIRO in Australia.
Einstein's famous equation E = mc2 needs to be taken into account when considering the effect of the radiation on the motion of the pulsar. This radiation has a mass loss of 8 million tonnes per second. It is only a tiny fraction of the mass of the pulsar per second.
The results join a growing body of high precision measurements of Einstein's predictions. The space-time around a black hole is consistent with general relativity, as is the timing of atomic clocks, a triple-star system and 14 years' worth of observations of a wobbly pulsar.
As more powerful telescopes emerge, we are likely to see even more precise tests of gravity, as scientists continue to look for holes.
General relativity is not compatible with quantum mechanics. Robert Ferdman is an astronomer at the University of East Anglia in the UK.
Any deviation from general relativity would be a major discovery that would open a window on new physics. It may help us discover a unified theory of nature.
The research has been published.
