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Ling Xin

China’s FAST telescope has compiled the world’s largest catalogue of neutral hydrogen beyond the Milky Way, replacing a long-dominant US survey as the main reference for mapping the gas that fuels the formation of stars and galaxies.
The FAST All-Sky H I Survey (FASHI), conducted with the 500-metre (1,640-foot) radio dish in southwest China’s Guizhou province, released its second batch of data this week. It contains 156,411 extragalactic sources – nearly five times the number detected by the now-defunct Arecibo Telescope in Puerto Rico.
The publicly available data gives astronomers worldwide an unprecedented pool of galaxies to investigate some of the universe’s biggest questions – from how the vast cosmic web took shape, to why some galaxies thrive while others fade away.
Compared with ALFALFA – the landmark US survey carried out with Arecibo from 2005 to 2012 – FASHI covered about three times as much sky and detected galaxies that were much smaller, fainter and further away, a team led by researchers from the National Astronomical Observatories reported.
The work established “a legacy data set that bridges the gap” between earlier surveys and the coming Square Kilometre Array – a massive international radio telescope now being built in Australia and South Africa, they wrote in a study published in the peer-reviewed journal Science China Physics, Mechanics & Astronomy this month.
For more than half a century, Arecibo’s 305-metre dish was an icon of radio astronomy.
Completed in 1963, it remained the world’s largest single-aperture radio telescope until FAST overtook it in 2016, and was behind a string of major astronomical discoveries before its giant observing platform collapsed in 2020.


Built into a natural depression in the mountains of Guizhou, FAST’s 500-metre reflector gives it greater sensitivity, while its ability to observe 19 patches of sky at once – compared with Arecibo’s seven – allows it to scan large areas much faster.
One of FAST’s key targets is neutral hydrogen, the basic form of the universe’s most abundant element and the raw material for making stars.
Its atoms give off a distinctive radio signal with a wavelength of 21cm (8.2 inches) that can pass through cosmic dust, revealing vast reservoirs of gas otherwise difficult to see.
FASHI began systematically searching for that signal in 2020. Its first data release in January 2024 catalogued 41,741 galaxies – already surpassing ALFALFA’s final tally of roughly 31,500.
The new release, based on observations through July 2025, nearly quadrupled that number. The huge sample could shed light on some of the universe’s least visible mysteries, such as how ordinary matter was distributed within the invisible framework of dark matter.
The first FASHI release quickly gained international attention, with its paper cited more than 100 times since 2024, according to the National Astronomical Observatories.
The full second release is now open to researchers worldwide, allowing teams to mine the data for their own studies. It could also serve as a benchmark for the next generation of radio surveys, including those planned with the Square Kilometre Array.
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China

Survey identifies more than 156,000 extragalactic sources, offering an unprecedented pool for studying the universe’s biggest questions


Survey identifies more than 156,000 extragalactic sources, offering an unprecedented pool for studying the universe’s biggest questions.


United States

China’s FAST telescope maps neutral hydrogen, the cosmic gas for making stars

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}Survey identifies more than 156,000 extragalactic sources, offering an unprecedented pool for studying the universe’s biggest questions

Survey identifies more than 156,000 extragalactic sources, offering an unprecedented pool for studying the universe’s biggest questions