FAST's New Discovery Reshapes Understanding of Early Universe

China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) has detected 156,411 neutral hydrogen sources across nearly half the sky, marking a major breakthrough in radio astronomy. These findings, published in *Science China Physics, Mechanics & Astronomy*, provide new insights into galaxy formation and evolution, dark matter distribution, and large-scale cosmic structures. The data, dubbed FASHI DR2, extends the neutral hydrogen mass function to galaxies of about one million solar masses and provides the most accurate measurement of local neutral hydrogen density to date.