A committee of the National Science Foundation (NSF) has recommended closing six major astronomy facilities in favour of building and supporting new telescopes. The observatories under threat include two leading radio telescopes – the Green Bank Telescope (GBT) in West Virginia and the Very Large Base Array (VLBA), which comprises 10 radio-dish antennas spread across the US from Hawaii to the US Virgin Islands. They are joined by four others based at Kitt Peak in Arizona – the Mayall Telescope, the Wisconsin-Indiana-Yale-National Optical Astronomy Observatory, a 2.1 m telescope and the McMath-Pierce Solar Telescope. US astronomers fear that if the telescopes close it will jeopardize the country's position as a world leader in astronomy.

The NSF's astronomy portfolio review, chaired by astronomer Daniel Eisenstein from Harvard University, calls for the NSF to stop supporting the six facilities within the next five years. Given tougher budget conditions for the NSF, the money saved from such closures would go towards supporting newer facilities such as Atacama Large Millimeter/submillimeter Array (ALMA), the Advanced Technology Solar Telescope and eventually the Large Synoptic Survey Telescope.

The VLBA, with a "baseline" of more than 5000 miles, makes it the largest in the world, with the GBT sporting the largest steerable radio dish at 100 m across. However, the 17-person NSF committee believes that other radio telescopes could take on the workload of the GBT and that the capabilities of the VLBA to precisely measure the position and movements of stars has not been deemed a priority in the recent Astrophysics Decadal Survey. "We were charged to recommend the best possible overall portfolio in light of the budget constraints and the Decadal Survey science priorities," says Einsenstein. "Hard choices have to be made."

"A huge surprise"

Many astronomers, however, are not satisfied with the committee's recommendations. "The loss of the GBT and the VLBA will be a blow to astronomers within the US and around the world," says GBT site director Karen O'Neil. "Implementation of the recommendations will have a serious impact on the accessibility of major astronomy facilities to US observers as competition for those facilities becomes extremely high."

Michael Kramer of the Max Planck Institute for Radio Astronomy in Bonn, which operates the German-based Effelsberg 100-m Radio Telescope, says that the GBT is one of the most important radio telescopes in the world, as its location in a radio quiet zone in the northern hemisphere is unique. "The report has come as a huge and unpleasant surprise," says Kramer. "I cannot follow the arguments of the report and find it particularly difficult to accept the report's conclusions."

That view is shared by Tony Beasley who is director of the National Radio Astronomy Observatory, which operates the GBT and the VLBA. "We are pleased that ALMA and the Very Large Array were highly ranked, but the loss of the GBT and VLBA would break up the quartet of the best radio facilities in the world, which cover nearly the entire range of resolution, wavelength coverage and imaging capability," he adds.

However, there may still be a lifeline for the VLBA and GBT as well as the other four telescopes affected in the committee's report. Although the recommendation calls for the NSF to cease funding of the observatories, other funding sources could be found to keep them running in the long-term, such as private investment. "The report recommends divestment, which need not be the same as closure," says Eisenstein. "We are recommending an end to NSF funding but there are many possible implementations of that."