Einstein is proven right yet again — this time on a galactic scale

Once again, Albert Einstein's general theory of relativity has held up — this time in another galaxy.

Using data from NASA's Hubble Space Telescope and the European Southern Observatory's Very Large Telescope, an international team of researchers found that gravity in a galaxy millions of light-years away behaves how the renowned physicist's theory predicted.

"It is so satisfying to use the best telescopes in the world to challenge Einstein, only to find out how right he was," said researcher Bob Nichol of England's University of Portsmouth.

The team's findings were published this week in the journal Science.

One property of gravity described by Einstein is that objects with considerable mass can bend the light of distant objects. This was first proven in the Milky Way during an eclipse in 1919, when astronomer Arthur Eddington witnessed deflected light from a star that appeared near the sun.

This phenomenon, called "gravitational lensing," can be quite dramatic when massive galaxies bend the light of galaxies that lie behind them. This is known as "strong gravitational lensing."

Most of these strong gravitational lenses are too distant for astronomers to measure the mass of the galaxy responsible for bending the light. But Nichol and the team decided to test the theory on one of the nearest galaxies, ESO 325-G004, which lies 500 million light-years from Earth.

They measured how fast the stars were moving within the galaxy, which in turn allowed them to calculate how much mass ESO 325-G004 had in order to keep them in orbit (rather than flinging outward into space). They then compared the mass to the lensing observed by the Hubble Telescope. 

Thomas Collett, an astronomer at England's University of Portsmouth and lead author of the study, explains the findings.

The researchers found the galaxy's mass was within nine per cent of what the general theory of relativity predicted.

"The universe is an amazing place providing such lenses," Nichol said, "which we can use as our laboratories."