Einstein's General Relativity Proven to Work in 'Extreme Gravity'

The pulsar and the inner white dwarf are in a 1.6-day orbit. This pair is in a 327-day orbit with the outer white dwarf, much further away. SKA organization

An international team of astronomers has conducted a new test of Albert Einstein's famous theory of general relativity (GR), finding that it works even in extreme gravitational environments, according to a study published in the journal Nature.

Since the great German physicist published his groundbreaking theory in 1915—which describes the nature of gravity—it has been tested numerous times by scientists around the world.

However, while GR has passed most of these tests, some researchers hypothesize that there are certain situations where alternative theories of gravity could be at play. Such situations could include instances of extreme gravity, for example.

So, to test GR in extreme gravity, the researchers conducted observations of a massive three-star system known as PSR J0337+1715, located 4,200 light-years from Earth, which was discovered by the same astronomers in 2014.

PSR J0337+1715 consists of two white dwarfs and a neutron star. White dwarfs are small, dense stars comparable in size to the Earth, but with a mass closer to the Sun. Neutron stars, on the other hand are even smaller and denser. They form after a massive star explodes as a supernova when it comes to the end of its life, a process which sees the core collapse.

The neutron star in PSR J0337+1715 is what's known as a pulsar—a highly magnetized, rapidly rotating neutron star which emits beams of electromagnetic radiation through space like a lighthouse. These beams can be detected on Earth.

The researchers tracked the star system for six years using the Green Bank Telescope in West Virginia, the Arecibo Observatory in Puerto Rico and the Westerbork Synthesis Radio Telescope in the Netherlands.

In the system, the neutron star is in orbit with one of the white dwarfs, while the second white dwarf orbits both of these stars. By tracking the trio, the scientists wanted to find out whether the neutron star and inner white dwarf were affected differently by the gravity of the outer white dwarf.

However, the scientists found practically no detectable difference, indicating that general relativity describes this scenario accurately, meaning alternative theories of gravity are not required.

"If there is a difference, it is no more than three parts in a million," Nina Gusinskaia, a co-author of the study from the University of Amsterdam, said in a statement. "Now, anyone with an alternative theory of gravity has an even narrower range of possibilities that their theory has to fit into, in order to match what we have seen."

According to Ingrid Stairs, another co-author of the study from the University of British Columbia, it is important for scientists to keep testing general relativity.

"Every single time we've tested Einstein's theory of relativity so far, the results have been consistent," she said. "But we keep looking for departures from relativity because that might help us understand how to describe gravity and quantum mechanics with the same mathematical language."

Einstein's theories have been receiving significant attention lately among researchers.

A recent study, published in the journal Science, also tested GR, confirming that it works even in a distant galaxy—something that has never been demonstrated before.

Meanwhile, findings from another Science study have bolstered another theory first proposed by the physicist in 1911, which describes how heat moves through solids.