A survey of the stars using the Hubble Space Telescope has confirmed the accelerating expansion of the universe and Einstein's ideas about gravity, a team of astronomers said.
Astronomers from North America and Europe, including Ludovic Van Waerbeke of the University of British Columbia, studied more than 446,000 galaxies to create a map of the distribution of matter in the universe.
This 3-D map of the universe includes the distribution of dark matter, material that gives off no light but whose existence is seen in how its gravity interacts with stars, galaxies and even light itself.
The survey, published this week in the journal Astronomy & Astrophysics, confirmed that the universe is expanding at an accelerating rate, propelled by a mysterious force called dark energy.
"Our results confirmed that there is an unknown source of energy in the universe which is causing the cosmic expansion to speed up, stretching the dark matter further apart exactly as predicted by Einstein's theory," said Van Waerbeke in a statement.
The astronomers were able to find where the dark matter is using a technique called weak gravitational lensing, where light from distant galaxies is observed to bend as it travels through space.
The General Theory of Relativity, a manuscript published by Albert Einstein in 1915, holds that gravity arises because matter warps space and time, meaning that light bends near massive objects, such as the core of a galaxy.
Even a less massive object, such as a clump of dark matter, can cause light to bend slightly. Van Waerbeke has used weak gravitational lensing since the late 1990s to map structures of dark matter by measuring the distortions seen in the patterns of light from galaxies.
Einstein's theory also predicted the existence of dark matter, to explain the "missing" matter that doesn't give off light and makes up 80 per cent of the mass of the universe, and dark energy, to explain the universe's accelerating expansion.
"The data from our study are consistent with these predictions and show no deviation from Einstein's theories," said Van Waerbeke.
The survey also used data from the Cosmic Evolution Survey (COSMOS), which used the Hubble telescope to photograph 575 slightly overlapping views of the same patch of sky.
The COSMOS project required nearly 1,000 hours of observations to complete. Like Hubble itself, COSMOS is a joint operation of the European Space Agency and NASA.
Observations from ground-based telescopes were also used to calibrate the distances of the more than 194,000 galaxies mapped during the survey.