Astrophysicists have designed a simulation to test and rule out existing theories of gravity
Albert Einstein’s theory on gravity, which he published over a 100 years ago still explains important solar details like planets and their orbits, and the bending of starlight in his thesis general relativity (GR). Physicists are still trying to invent new theories that couldn’t be explained in GR, such as explaining the need for invisible dark matter, whose gravity is believed to bind the galaxies.
After seeing the image of a black hole for the first time last year, proving theories of gravity turned out to be much more harder. “It’s a new hoop to jump through and a fairly narrow one,” says Feryal Özel, an astrophysicist at the University of Arizona, and a member in devising the new test.
The test
In the image we got last year, we see a fiery ring surrounding a black dot, the glow being the hot gas that surrounds the black hole. The dot is the “shadow” cast by the black hole. The scientists sought the help of the Event Horizon Telescope (EHT) and used GR to calculate the size of the shadow, which has been magnified by the black hole’s gravity, and found out that their results agreed with their observation.
Özel stated that this image couldn’t be used to test out other theories of gravity, as they don’t have any easy way to determine the size of the shadow. Özel and team have developed a fairly easy way to get that calculation, as reported in this week’s Physical Review Letters. Inorder to test a new theory, researchers will only need to calculate the value it predicts for the second post-Newtonian parameter, and if the value falls outside a set range, it’s not applicable. Judging by the shadow, the team narrowed the range for the parameter by a factor of 500.
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Researchers are opting for post-Newtonian parameters and if any of those work out, then it can be confirmed that GR is not the final verdict on gravity.
(Cover: NASA)