October 9, 2008
Relativity Passes Latest Test
A study of two unequal mass stars in close orbits has produced results in keeping with Einstein's theory of general relativity. "Einstein's theory predicts that stars in such a system will come closer and closer to each other as they lose energy due to gravitational radiation," says Dr Rhamesh Bhat of Swinburne University's Centre for Astrophysics and Supercomputing. "Previous research has supported Einstein's theory in this context."Such tests are applied quite frequently (AS, Nov/Dec 2006, p.42), and general relativity keeps passing, but some alternative theories so far remain viable as well. Bhat's test differed from past trials in that the two stars were of significantly different masses and densities. Some alternatives to general relativity offer different predictions on what should occur when a stellar pair has uneven densities.
In this case the system is made up of a neutron star that has a mass greater than the Sun but is the size of a city, and a white dwarf with a mass similar to the Sun's and a diameter more like that of the Earth.
"Einstein's theory predicts that the pair's orbit should shrink at a rate of approximately 2 mm/day," says PhD student Joris Verbiest. Some other theories predict slightly different rates of shrinkage, but 7 years of observations have measured shrinkage at just the rate Einstein expected.
Bhat says that observations taken over a longer timeline will increase the accuracy of the measurements, providing even more certainty that general relativity is correct.
The study was published in Physical Review.
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