FAST will enable highly sensitive measurements of astronomical phenomenon.Credit: Ou Dongqu/Xinhua/ZUMA

The world’s largest single-dish radio observatory is preparing to open to astronomers around the world, ushering in an era of exquisitely sensitive observations that could help in the hunt for gravitational waves and probe the mysterious fleeting blasts of radiation known as fast radio bursts.

The Five-hundred-meter Aperture Spherical Radio Telescope (FAST) in southern China has just passed a series of technical and performance assessments, and the Chinese government is expected to give the observatory the final green light to begin full operations at a review meeting scheduled for next month. “We do not see any roadblocks for the remaining transition,” says Di Li, the chief scientist of FAST. “I feel both excited and relieved.”

The complex project has not been without challenges — it has a radical design and initially struggled to attract staff, in part because of its remote location. But the pay-off for science will be immense. FAST will collect radio waves from an area twice the size of the next-largest single-dish telescope, the Arecibo Observatory in Puerto Rico.

The Chinese observatory’s massive size means that it can detect extremely faint radio-wave whispers from an array of sources across the Universe, such as the spinning cores of dead stars, known as pulsars, and hydrogen in distant galaxies. It will also explore a frontier in radioastronomy — using radio waves to locate exoplanets, which may harbour extraterrestrial life.

Since testing began in 2016, only Chinese scientists have been able to lead projects studying the telescope’s preliminary data. But now, observation time will be accessible to researchers from around the world, says Zhiqiang Shen, director of the Shanghai Astronomical Observatory and co-chair of the Chinese Academy of Sciences’ FAST supervisory committee.

“I’m super excited to be able to use the telescope,” says Maura McLaughlin, a radioastronomer at West Virginia University in Morgantown, who wants to use FAST to study pulsars, including hunting for them in galaxies outside the Milky Way, that are too faint to see with current telescopes.

During the testing phase, the telescope discovered more than 100 pulsars.

Eye in the sky

The 1.2-billion-yuan (US$171-million) telescope, also known as Tianyan or ‘Eye of Heaven’, took half a decade to build in the remote Dawodang depression in the Guizhou province of southwest China. Its 500-metre-wide dish is made up of around 4,400 individual aluminium panels that more than 2,000 mechanical winches tilt and manoeuvre to focus on different areas of the sky. Although it sees less of the sky than some other cutting-edge radio telescopes, and has lower resolution than multidish arrays, FAST’s size makes it uniquely sensitive, says Li.

In August and September, the instrument detected hundreds of bursts from a repeating fast radio burst (FRB) source known as 121102. Many of these bursts were too faint to be perceived by other telescopes, says Li. “This is very exciting news,” says Yunfan Gerry Zhang, who studies FRBs at the University of California, Berkeley. No one knows what causes the mysterious bursts, but “the more pulses we have, the more we can learn about them”, he says.

FAST examines only a tiny fraction of the sky at any one time, making it unlikely to discover many new FRBs, which are fleeting and occur in seemingly random locations. But the telescope’s “impressive sensitivity” will be useful for following up on sources in detail, says Laura Spitler, an astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany. Repeat observations could allow scientists to learn about the environment from which an FRB emerged, and to determine whether the blasts vary in energy or recur with any set pattern.

FAST will also boost the efforts of an international collaboration that is trying to spot ripples in space-time as they sweep through the Galaxy, says McLaughlin. The International Pulsar Timing Array is using radio telescopes around the world to monitor the regular emissions from pulsars, looking for distortions that would reveal the passing of these low-frequency gravitational waves. By the 2030s, FAST should have racked up enough sensitive measurements to study individual sources of such waves, such as collisions of supermassive black holes, says McLaughlin. “That’s where FAST is really going to shine,” she says.

Li says that he is particularly excited about the study of planets outside the Solar System. No exoplanets have yet been conclusively detected by their radio emissions, but FAST’s ability to spot faint, polarized waves might allow it to find the first examples, says Li. Polarized radio signals might come from planets with magnetic fields that, if similar to the one on Earth, could protect potential sources of life against radiation and keep the planets’ atmospheres attached.

Identifying a planet in FAST’s wide beam is a challenge, because they are so faint and small. But Li’s team wants to boost the telescope’s performance by adding 36 dishes, each 5 metres wide. Although the dishes are relatively cheap, off-the-shelf products, together they will improve FAST’s spatial resolution by 100 times, he says.

Li hopes that FAST’s telescope operations will soon move from near the remote site to a $23-million data-processing centre being built in the city of Guiyang. He expects that the move to a major city will help attract more technical and engineering staff.

Now the team’s biggest hurdle is working out how to store and process the enormous amount of data that the telescope will churn out. The team are negotiating with the Chinese government to get additional funding for more data storage. “A successful review will definitely help,” he says.