The world's largest and most powerful gamma-ray observatory looks set to be based in Chile and the Canary Islands, following a decision today by the governing board of the Cherenkov Telescope Array (CTA). Sites in the Atacama Desert and the island of La Palma—already home to major astronomical facilities—were chosen ahead of rival sites in Namibia and Mexico for the northern and southern portions of the CTA, a €297 million facility that will allow astrophysicists to study some of the most energetic and distant objects in the universe.
The decision came during a 2-day meeting of the CTA Resource Board on 15 and 16 July. The board, made of representatives from 14 of the project’s 31 member countries, did not give final approval for the site selection—that is the job of the CTA Council—but it did vote to start formal negotiations with the European Southern Observatory (ESO), which operates the Paranal Observatory in Chile, and Spain.
Chair of CTA Resource Board Beatrix Vierkorn-Rudolph would not tell ScienceInsider how the 14 members voted. But she says it was not an easy decision, since all 4 bidders put forward "very good sites." The selection criteria were many, she explains, including the sites' environmental suitability, scientific potential, and likely cost. But one factor stood out in both cases, she says—how swiftly construction could get underway once the official green light has been given.
The Chilean site is less than 10 kilometers from the ESO’s Paranal Observatory, which has significant infrastructure—like the four, 8.2-meter optical observatories of the Very Large Telescope—already in place. The northern site, which is operated by the Institute of Astrophysics of the Canaries, sits at an altitude of 2200 meters and is already home to the 2 MAGIC gamma-ray telescopes (pictured above).
The CTA, which should be completed by around the end of the decade, would allow scientists to carry out a range of research projects across astrophysics and fundamental physics, from the origin of cosmic rays to particle acceleration around black holes. The array would also look for signs of hypothetical dark matter particles. It would comprise 120 individual telescopes of 3 different diameters (24, 10-12, and 4-6 meters), about 100 of which would be located in the southern hemisphere. Like existing ground-based gamma-ray observatories, the telescopes wouldn't detect gamma rays directly but would instead pick up the flashes of light given off when gamma radiation interacts with atoms in the upper atmosphere.
Rene Ong, an astrophysicist at the University of California Los Angeles and CTA co-spokesperson, says that negotiations with the hosts of the preferred sites should take about 6 months. During that time, he says, CTA member countries will need to establish, among other things, whether money offered as part of the site bids really will be made available. He says that Spain has offered to contribute "upwards of €40 million" in support of the La Palma site, while ESO has not made any financial offer but is interested in partnering on the science and management of CTA. He also notes that the ESO council has still to formally approve its site proposal.
Ong says that a number of member countries have shown a "strong intention" to provide funding for the project. However, the threshold of about 80% funding—at which point construction could be approved—has yet to be reached. He hopes the line can be crossed in the next year. If it isn't, he says, the project scope may need to be “adjusted.”