The South African Radio Astronomy Observatory has announced that its Chief Scientist, Dr Fernando Camilo, was a member of an international team of 29 scientists from ten countries who have successfully concluded a 16-year experiment to test the renowned physicist Albert Einstein‘s Theory of General Relativity. The team used data from seven radio telescopes in six countries (Australia, France, Germany, the Netherlands, the UK and the US), plus a very long baseline array (composed of ten dishes, all aimed at the same target at the same time) in the US. Yet again, Einstein’s theory held up.

The focus of the experiment was a unique pair of pulsars, discovered in 2003. Pulsar was originally an acronym for pulsating star, the term applied to them when they were first discovered in 1967. However, they are not pulsating; rather, they are magnetised neutron stars that emit rotating beams of radiation. These radiation beams appear to an observer to be periodic because they are detectable only when they sweep across the observer’s line-of-sight (like the beam from a lighthouse). Neutron stars themselves are the collapsed cores of massive stars which, at the end of their lives, exploded into supernovas. Neutron stars are incredibly dense, with a diameter of only about 24 km, yet a mass greater than that of the Sun.

The double pulsar, designated PSR J0737-3039 A/B, is located at a distance of 2 400 light years, in the direction of the constellation Puppis. The two pulsars orbit each other in just 147 minutes. One of them rotates around its axis 44 times every second, while the rotation period of the other is 2.8 seconds. One of the results of this situation is that the radiation emissions of one pulsar are eclipsed by the magnetosphere (the volume dominated by the magnetic field) of the other. Another crucial consequence is the creation and maintenance of very strong gravitational fields.

“We studied a system of compact stars that is an unrivalled laboratory to test gravity theories in the presence of very strong gravitational fields,” explained Max Planck Institute for Radio Astronomy professor, and research team leader, Michael Kramer. “To our delight 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 Nobel Prize-winning Hulse-Taylor pulsar, and 1 000 times better than currently possible with gravitational wave detectors.”

“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,” reported University of British Columbia in Vancouver Prof Ingrid Stairs. “We see for the first time how the light is not only delayed due to a strong curvature of spacetime around  the companion, but also that the light is deflected by a small angle of 0.04 degrees that we can detect. Never before has such an experiment been conducted at such a high spacetime curvature.”

The research team was able to test seven of the predictions in Einstein’s Theory of General Relativity. All seven passed the tests. In fact, Einstein’s predictions agreed with the observations of the double pulsar system at a level of, at a minimum, 99.99%.

“These wonderful results show the value of patient long-term studies carried out with world-leading research facilities,” stressed Camilo. “Much remains to be learned about this remarkable natural laboratory, to which South Africa’s MeerKAT [radio telescope array] is now contributing with its observations of unsurpassed quality.”