China’s massive FAST radio telescope has created the world’s largest catalogue of neutral hydrogen beyond the Milky Way, giving astronomers an unprecedented map of the gas that provides the raw material for stars and galaxies.
The second release from the FAST All-Sky H I Survey, or FASHI, contains 156,411 extragalactic sources. That is nearly five times the number identified by the former Arecibo Observatory in Puerto Rico, whose surveys had long been a major reference for studies of neutral hydrogen.
Neutral hydrogen is particularly important to astronomers because it serves as a reservoir of material from which stars can eventually form. By mapping where this gas is located across distant galaxies, scientists can investigate how galaxies grow, evolve and sometimes stop producing new stars.
FAST, formally known as the Five-hundred-meter Aperture Spherical Radio Telescope, is located in a natural depression in Guizhou province in southwestern China. Its 500-metre dish became the world’s largest single-dish radio telescope when it overtook Puerto Rico’s 305-metre Arecibo telescope in 2016.
The new FASHI survey covers roughly three times more sky than the landmark ALFALFA survey conducted with Arecibo between 2005 and 2012. FAST has also been able to detect galaxies that are smaller, fainter and farther away, expanding the range of objects available for detailed study.
The newly released catalogue could help scientists investigate some of astronomy’s biggest questions, including how the universe’s vast cosmic web developed and why some galaxies continue forming stars while others gradually become inactive.
Researchers describe the dataset as an important bridge between earlier neutral-hydrogen surveys and the next generation of radio astronomy facilities, including the international Square Kilometre Array being built in Australia and South Africa.
FAST’s work is also significant because neutral hydrogen emits radio signals at a wavelength of about 21 centimetres. Those signals can travel across enormous distances, allowing radio telescopes to trace the distribution and movement of hydrogen even when galaxies are difficult to observe using visible light.
The survey data is being made available to astronomers, creating a large resource for researchers around the world. With more than 156,000 extragalactic sources now catalogued, scientists have a much larger sample with which to compare galaxies and examine how their gas supplies are connected to their evolution.
For astronomy, the achievement is less about producing a single dramatic discovery than creating a vast new map of the universe. By charting the cosmic gas that ultimately feeds star formation, FAST is giving researchers a clearer way to study how galaxies emerge, change and develop across cosmic history.
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