An international team of astronomers has confirmed that the expansion of the universe is accelerating after looking at new data from the largest-ever survey conducted by the Hubble Space Telescope. The results of the research will appear in Astronomy and Astrophysics.

Researchers studied more than 446,000 galaxies to map the matter distribution and the expansion history of the universe. They were able to observe precisely how dark matter evolved in the universe and to reconstruct a three-dimensional map of the dark matter and use this to test Albert Einstein's theory of general relativity.

An international team of astronomers has confirmed that the expansion of the universe is accelerating after looking at new data from the largest-ever survey conducted by the Hubble Space Telescope. The results of the research will appear in Astronomy and Astrophysics.

Researchers studied more than 446,000 galaxies to map the matter distribution and the expansion history of the universe. They were able to observe precisely how dark matter evolved in the universe and to reconstruct a three-dimensional map of the dark matter and use this to test Albert Einstein's theory of general relativity.

A smoothed reconstruction of the total (mostly dark) matter distribution in the COSMOS field, created from data taken by the NASA/ESA Hubble Space Telescope and ground-based telescopes. It was inferred from the weak gravitational lensing distortions that are imprinted onto the shapes of background galaxies.

The color coding indicates the distance of the foreground mass concentrations as gathered from the weak lensing effect. Structures shown in white, cyan and green are typically closer to us than those indicated in orange and red.

(Photo Credit: NASA, ESA, P. Simon (University of Bonn) and T. Schrabback (Leiden Observatory))

"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," says University of British Columbia astronomer Ludovic Van Waerbeke.

Einstein's theory of general relativity predicts that space and time is a soft geometrical structure of which the shape and evolution are entirely determined by the matter within it. Scientists posit that the universe is composed of dark matter and normal matter with a third constituent called "dark energy," which over the past two billion years has been the force behind the accelerated expansion of the universe.

"The data from our study are consistent with these predictions and show no deviation from Einstein's theories," says Van Waerbeke.

The discovery was made using weak gravitational lensing, a technique that measures the invisible web of dark matter that makes up 80 per cent of the mass of the universe. This technique is similar to taking an X-ray of the body to reveal the underlying skeleton. It allows astronomers to observe how light from distant galaxies is bent and distorted by the web of invisible dark matter as it travels toward Earth. By measuring the distortions seen in these galaxy light patterns, astronomers can then map dark matter structures.

Researchers also relied on data from the Cosmic Evolution Survey (COSMOS), one of the most ambitious undertakings by the Hubble Space Telescope. COSMOS is a joint project of the European Space Agency (ESA) and NASA involving more than 100 scientists from a dozen countries.

To generate the COSMOS survey, a camera aboard the Hubble photographed 575 slightly overlapping views of the same part of the universe. This required nearly 1,000 hours of observations, during which Hubble circled the Earth almost 600 times.

Citation: Schrabback et al., 'Evidence for the accelerated expansion of the Universe from weak lensing tomography with COSMOS', Astronomy and Astrophysics, March 2010,