Construction has begun on a massive new 500 m diameter radio telescope in Guizhou province, China, that will allow astronomers to detect galaxies and pulsars at unprecedented distances. The $102m facility, known as the Five-hundred-meter Aperture Spherical Telescope (FAST), will boast a collecting area equal to 30 football fields — more than twice as big as the 305 m diameter radio telescope at Arecibo Observatory in Puerto Rico, which has been the world’s largest since it opened in 1964.

The geography and remoteness of FAST’s site — located some 170 km by road from the provincial capital Guiyang, near the village of Dawodang — make it unusually radio-quiet, says Nan Rendong, FAST chief scientist and a researcher from the National Astronomical Observatories at the Chinese Academy of Sciences. Like Arecibo, the new telescope will sit in a natural karst depression that mimics the shape of the collecting surface, simplifying the support structure and shielding the telescope from stray human-generated radio waves.

The site’s potential for long, uninterrupted observations — coupled with the telescope’s huge size, which will give it twice the sensitivity of Arecibo — means that researchers there will be able to detect objects like weak, fast-period pulsars that are too faint to be measured accurately by smaller instruments. The team also expects to discover the first pulsar outside the Milky Way, according to Nan.

'Extraordinary' impact on astronomy

“The FAST science impact on astronomy will be extraordinary,” Nan told physicsworld.com, adding that although the telescope is located in China, once it is completed in 2014 it will be open to astronomers from around the world.

In addition to being big, FAST is designed to be flexible: a system of motors attached to its 4600 panels will allow astronomers to change its shape from a sphere to a paraboloid, making it easier to move the position of the telescope’s focus. This will allow the south-pointing telescope to cover a broad swathe of the sky — up to 40 degrees from its zenith, compared to the 20-degree-wide strip covered by Arecibo.

“Arecibo points straight up, and it’s a real chore to move more than 20 degrees,” says Murray Lewis, head of the radio astronomy group at Arecibo. “In that respect, they definitely have an advantage.” However, he notes that in its initial phase, FAST will only be sensitive to low-frequency (less than 3 GHz) radio waves. This range includes the commonly observed 1.4 GHz hyperfine transition in atomic hydrogen, the universe’s most abundant element and an important marker for a variety of stellar objects. Arecibo’s bandwidth, by contrast, stretches up to 10 GHz, allowing astronomers to collect data on molecular transitions in this region of the spectrum.

A planned second phase of construction will extend FAST’s range to 5 GHz, but a date for the upgrade has not yet been set.