Published: Fri, July 06, 2018
Science | By Joan Schultz

Albert Einstein’s gravity theory passes another test yet again

Albert Einstein’s gravity theory passes another test yet again

In a novel test of Einstein's theory of general relativity, an worldwide group of astronomers has demonstrated that the theory holds up, even for a massive three-star system. An global research team led by the Anton Pannekoek Institute of Astronomy at the University of Amsterdam, in the Netherlands, has shown that the equivalence principle, which holds that all bodies in the same gravitational field are equally accelerated, is correct.

Apollo 15 astronaut David Scott dropped a feather and a hammer on the Moon.

This is because Einstein's principle of gravity has just been proven right by yet another major science experiment, making it increasingly hard for alternative gravity theories to demonstrate their case.

To date, Einstein's equations have passed all tests, from careful lab studies to observations of planets in our Solar System. Over time, the researchers found nearly no detectable difference, indicating there is little room for alternative theories of gravity in this model. That difference, these alternate theories predict, would be due to a compact object's so-called gravitational binding energy - the gravitational energy that holds it together.

The proven theory comes after the university studied a three-star system known as PSR J0337+1715, which is located 4,200 light years away and is made up of two white dwarfs and a neutron star.

"This particular system consists of one ultra-dense neutron star and two less-dense white dwarf stars, which makes these stars the dream team for testing relativity", senior lecturer Adam Deller from Swinburne's Center for Astrophysics and Supercomputing, who was involved in the project.

"We know that the theory will ultimately break down when trying to describe the singularities of black hole", Lorimer added.

"Fortunately, 30 meters was still a very stringent test of Einstein's theory", Archibald said.

Lorimer and the team of astronomers followed the neutron star for six years using the Green Bank Telescope in West Virginia, the Westerbork Synthesis Radio Telescope in the Netherlands and the Arecibo Observatory in Puerto Rico. The GBT has spent more than 400 hours observing this system, taking data and calculating how each object moves in relation to the other. It's called the equivalence principle, and scientists just showed it holds firm using a distant triple-star system discovered in 2012.

Astronomers compared the rate of fall of a feather and the dense bodies in the Universe - a neutron star. "As one of the most sensitive radio telescopes in the world, the GBT is primed to pick up these faint pulses of radio waves to study extreme physics", Lynch said. We have used these radio pulses to track the position of the neutron star.

"We can account for every single pulse of the neutron star since we began our observations", said principle author Anne Archibald of the University of Amsterdam and the Netherlands Institute for Radio Astronomy.

While the pulsar was measured with radio observations, the team measured the motion of the inner companion's orbit based on optical observations, measuring the Doppler shifts of the white dwarf's spectrum, the same way some exoplanets are found.

The researchers were able to come to this conclusion by studying the movements of the neutron star.

Any difference between the accelerations of the neutron star and white dwarf is too small to detect.

"If there is a difference, it is no more than three parts in a million", Nina Gusinskaia, co-author of the study, said in another statement.

This triple star system provides a great test bed for the theory of relativity.

This, as the researchers described, not just rules out alternative theories of gravity but is also a 10 times more precise test than the best experiments conducted ever before.

"We're always looking for better measurements in new places, so our quest to learn about new frontiers in our Universe is going to continue", Dr. Ransom said.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under a cooperative agreement by Associated Universities, Inc.

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