China’s FAST telescope creates the largest catalog of neutral hydrogen
China’s FAST radio telescope in Guizhou Province has released the second data set of the FASHI survey, containing 156,411 extragalactic sources. It is the world’s largest catalog of neutral hydrogen beyond the Milky Way, the South China Morning Post reports.
Data for galaxy research
The FAST All-Sky H I Survey has been systematically searching for the radio signal of neutral hydrogen since 2020. Atoms of this most abundant element in the Universe emit a signal with a wavelength of 21 centimeters, which can pass through cosmic dust and reveal large gas reserves. Neutral hydrogen is the raw material for star formation.
The new catalog is nearly five times larger than the number of sources detected by the Arecibo telescope in Puerto Rico, which is no longer operational. FASHI data, based on observations through July 2025, are open to researchers worldwide. They can be used to study the formation of the cosmic web, the distribution of ordinary matter in the invisible structure of dark matter, and the evolution of galaxies.
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FAST advantages
Compared with the U.S. ALFALFA survey conducted at Arecibo in 2005–2012, FASHI covered an area of the sky approximately three times larger. The Chinese survey also detected smaller, fainter, and more distant galaxies. The final ALFALFA catalog contained about 31,500 objects, while the first FASHI release in January 2024 already included 41,741 galaxies.
FAST has a 500-meter reflector built in a natural mountain depression in Guizhou. The telescope can observe 19 areas of the sky simultaneously, while Arecibo could cover seven. Researchers from the National Astronomical Observatories noted in an article in the journal Science China Physics, Mechanics & Astronomy that the data set will become an intermediate link between previous surveys and future research involving the Square Kilometre Array in Australia and South Africa.
