The Square Kilometre Array (SKA) project will be hosted by South Africa and Australia, following a decision made by the SKA organization today.

SKA will be a €1.5bn ground-based radio-astronomy telescope used to probe the early universe for clues on galaxy evolution, dark matter and dark energy by looking as far back into time as the first 100 million years after the Big Bang. South Africa has been competing to host the array, with a rival bid from Australia.

Decision made

SKA organization members who did not bid to host the telescope (Canada, China, Italy, the Netherlands and the UK) voted to pick the host site in a meeting held in Amsterdam today. A majority of them voted for the dual-site solution. "This hugely important step for the project allows us to progress the design and prepare for the construction phase of the telescope," says Michiel van Haarlem, general director of the SKA organization.

The decision follows a report from the SKA Site Advisory Committee submitted in February, which suggested that both sites were well suited to hosting the project. Although the report identified South Africa as the preferred site, the SKA members also received advice from a separate working group that was set up to consider the dual-site option.

The initial plan was for a single large array to consist of 2000 to 3000 linked antennas spread from a central 5 km "core" that would contain about 50% of the collecting area, out to stations as far as 3000 km away. The array would then work as one telescope that would have the same collecting area as a steerable dish 1 km in diameter.

Global venture

Now, with two locations in mind, the array will be spread across South Africa and Australia (the array will extend into New Zealand too), with the precursor test dishes – the MeerKAT array in South Africa and the Australian Square Kilometre Array Pathfinder (ASKAP) in Australia – being included into the phase I of SKA.

The majority of SKA dishes in phase I will be built in South Africa, along with all the dishes and the mid-frequency aperture arrays for phase II. The antennas for the low-frequency aperture array for phases I and II will be built in Australia.

Stephen Serjeant, from the Open University in the UK, points out that the "split-site decision will involve some increased complication and cost". He says that both bids had built "tremendous national and international momentum and support, so any single-site decision would have been a very bitter blow to one community". "I'm confident that the SKA split-site decision will be to the lasting benefit of astronomy as a whole, as well as to the industrial bases in all the hosting countries," he says.

As well as the physical characteristics of the site, many other factors were taken into consideration while trying to pick a feasible location for SKA. These included having an area with very low levels of radio-frequency interference and the long-term sustainability of a radio-quiet zone. Long-distance data-network connectivity, the costs for operation and infrastructure, and even the political and working environments were taken into consideration.

"Today, we are a stage closer to achieving our goal of building SKA. This decision was reached after very careful consideration of information gathered from extensive investigations at both candidate sites," says John Womersley, chair of the SKA board of directors.