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Probing and proving gravity theory

Artist's impression of the J0348+0432 system.
[Image courtesy of European Southern Observatory / J. Antoniadis (MPIfR)]

Scientists have identified a neutron star, the densest kind of a star in the universe, which has helped them prove Einstein's theory of relativity in a place it's never been tested, a new study in Science reports.

General relativity (GR) was proposed by Einstein roughly a century ago and remains the best theory we have about how gravity works. Most scientists believe this theory holds true around Earth (where the pull of gravity is relatively weak) but they have not had the opportunity test it in places where the gravitational field is much stronger. Whether it holds up in such extreme environments remains unclear.

Now John Antoniadis at the Max Planck Institute for Radio Astronomy in Bonn, Germany, has tested this theory in a setting where the pull of gravity is very strong (much stronger than Earth).

Using spectroscopy—a method for identifying objects by studying how they interact with light—he and his colleagues identified a massive neutron star twice as heavy as the sun. The surfaces of neutron stars exhibit an extremely strong gravitational pull and thus create a perfect "laboratory" for testing Einstein's theory under strong gravity conditions.

This star had a special property that made it ideal for Antoniadis to study. Unlike other massive neutron stars known today, it was in a very tight orbit, requiring less than three hours to circle objects nearby it. This has made it possible to measure the way its orbit decays, or changes, because it fully orbits a star nearby it so often.

Since 2011, the researchers have been observing changes in this star's orbital decay. Thus far, they have found these changes to be consistent with the rate of decay predicted by Einstein's general relativity theory.

This observation provides support for the truth of Einstein's theory, even in the extreme conditions present in a system with a very strong gravitational pull.