Astronomers have taken an important step forward in the quest to solve the mystery of dark energy by using galaxies to magnify the distant Universe.

Normal matter like that making up stars and planets only comprises a tiny proportion of the Universe's mass-energy content; some 72 percent is dominated by dark energy, which is thought to control the expansion of the Universe, and 24 percent is dark matter, which despite being invisible exerts its gravitational influence on matter that we can see.

“We have to tackle the dark energy problem from all sides,” says Eric Jullo of NASA’s Jet Propulsion Laboratory. “It’s important to have several methods, and now we’ve got new, very powerful one.”

Using large galaxy clusters as giant magnifying lenses is a well-established technique for gleaning details of distant galaxies that would otherwise be too faint to study. As the Universe expands, the precise path that the light beams from the distant galaxies follow is bent and projected by the cluster’s massive gravitational pull in a similar way that the lens of a magnifying glass distorts an object’s image. The way in which the images are distorted provides vital information on the the geometry of the space that lies between the Earth, the cluster and the distant galaxies.

“The content, geometry and fate of the Universe are linked, so if you can constrain two of those things, you learn something about the third,” says Yale University cosmologist Priyamvada Natarajan.

Using the Hubble Space Telescope to study one of the most massive galaxy clusters in the Universe, Abell 1689, Natarajan and colleagues analysed 34 distant galaxies to yield clues on the nature of dark energy. Combining the Hubble data with that from the Wilkinson Microwave Anisotropy Probe (WMAP) and with data from supernovae and X-ray galaxies, the team were able to narrow the range of current estimates about dark energy’s effect on the Universe, denoted by the value w, by 30 percent.

“What I like about our new method is that it’s very visual,” says Jullo, “You can literally see gravitation and dark energy bend the images of the background galaxies into arcs.”

The result confirms previous findings that the nature of dark energy likely corresponds to a flat Universe, which suggest that the expansion of the Universe will continue to accelerate and the Universe will expand forever.

The results are reported in the 20 August issue of the journal Science.

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