Astronomers debunk hydrogen shortage theory for declining star formation

A new study published in Nature Astronomy has challenged long-held astrophysical models regarding why the rate of star formation in the universe has declined by approximately 60 percent over billions of years. Previously, scientists assumed that galaxies were slowing their stellar production because they were exhausting their reservoirs of cold gas.

However, research conducted by the Chinese Academy of Sciences in collaboration with the Dark Energy Spectroscopic Instrument (DESI) project reveals a mismatch between gas supply and star birth. By analyzing data from the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) and DESI, researchers found that while the star formation rate was roughly 2.5 times higher 4.5 billion years ago, the density of neutral atomic hydrogen—the primary fuel for stars—had only declined by a factor of 1.4.

This suggests that the slowdown in star formation is not caused by a simple shortage of hydrogen fuel. The team utilized a technique called HI spectral stacking to combine faint radio signals from millions of galaxies, allowing them to survey roughly one-third of the sky and overcome the difficulty of detecting weak 21-centimeter emissions from individual distant galaxies.