“China’s Tianyan creates the world’s largest neutral hydrogen galaxy database”

On September 8, 2026, the National Astronomical Observatories of the Chinese Academy of Sciences announced the release of the second-phase data from the Neutral Hydrogen Survey project of FAST. During the two-year observation period, the number of extragalactic neutral hydrogen sources detected by this project increased from 40,000 to 156,000, covering a sky area that expanded from 7,600 square degrees to 19,500 square degrees. This achievement surpassed the record held by the ALFALFA project of the Arecibo Telescope in the United States for nearly 20 years. The size of the second-phase dataset is approximately four times that of the first phase, with sensitivity reaching 0.57 milliayers per beam, which is about 0.7 times more sensitive than the ALFALFA project. Using this massive dataset, the research team was able to reliably measure the neutral hydrogen mass function up to 1 million times the mass of the Sun, and improve the measurement accuracy of nearby cosmic neutral hydrogen density to 0.6%. This dataset will provide important references for research on galaxy evolution and large-scale cosmic structures.