For five years, cosmologists and theoretical physicists have been wrestling with the bombshell discovery that a mysterious entity called 'dark energy' may be responsible for two-thirds of the energy and matter in the Universe.

Researchers are today no closer to defining dark energy, although they rely on it to explain the 1998 discovery that the Universe's expansion is accelerating, rather than slowing down under the influence of gravity, as had been widely assumed.

But they are at least closer to forging a plan to track it down. Last week, cosmologists met at the University of Chicago to hammer out a strategy to perform surveys of distant space that should glean more information about dark energy.

The plan involves constructing as many as 15 telescopes, including one in Antarctica, to work with existing ones in a bid to track thousands of clusters of galaxies. By looking at the distances between them, cosmologists hope to learn more about dark energy, which seems to make itself felt only between massive objects on a huge, intergalactic scale.

The survey will start by observing thousands of galaxy clusters up to 8 billion light years way. These clusters are observed now as they really were billions of years ago. If researchers compare the distances between these ancient clusters with those between clusters near our own galaxy — which can be observed pretty well as they are now — they may be able to establish how the clusters have been pushed apart, over time, by dark energy.

Finding and studying so many galactic clusters will be no small task, says John Carlstrom, a cosmologist at the University of Chicago who helped to organize the conference. Researchers will need to pick out clusters from the jumble of stars and galaxies in the night sky, and make precise measurements of the microwave radiation emitted by each cluster. Microwave radiation from space can easily be distorted by atmospheric water vapour, so much of the observation will be done by telescopes in very dry locations such as Antarctica.

Previous surveys of single galaxy clusters have taken several months using existing instruments, says Carlstrom. “My group has measured about 60 clusters in a decade,” he says. But with more powerful telescopes and faster data processing, the time needed should fall sharply. A 3.5-metre-diameter microwave telescope due to start observations later this year in Owen's Valley, California, will do in months what used to take years, he says.

In the long term, Carlstrom's group is also planning an $18-million, 8-metre-diameter microwave telescope at the South Pole, which will be able to do the same survey in a few hours when it starts operations in about four years' time. Other groups are planning similar projects in the Atacama Desert in Chile and on the mountaintops of Hawaii.

But questions remain about the effectiveness of the approach. For one thing, clusters of galaxies are unwieldy and awkward to define. “A cluster isn't like a star — it doesn't have a well-defined edge,” says August Evrard, a theoretical cosmologist at the University of Michigan in Ann Arbor.

Even so, Saul Perlmutter, an astronomer at the Lawrence Berkeley National Laboratory in California who led one of the groups that discovered dark energy, says the survey will represent an important step forward.