The universe has plenty of hydrogen. So why is star formation collapsing?
Star formation across the universe has fallen dramatically over the past 4.5 billion years, but astronomers have uncovered a surprising twist: the supply of neutral hydrogen, a key ingredient for making stars, has barely declined. Using China’s FAST radio telescope and data from roughly 2.5 million galaxies observed by DESI, researchers found that star formation was about 2.5 times higher 4.5…
The universe is producing fewer stars. Over the past 4.5 billion years, the rate of new star formation has dropped to less than half its previous level. Yet, the amount of neutral atomic hydrogen—a crucial fuel for star formation—has changed very little. This discrepancy, discovered by an international team led by scientists from the Chinese Academy of Sciences and the Dark Energy Spectroscopic Instrument project, raises new questions about the process of star formation.
Using the Five hundred meter Aperture Spherical radio Telescope (FAST) and DESI's large optical spectroscopy data set, the researchers measured cosmic neutral hydrogen across billions of years. They found that while star formation has fallen sharply, the overall amount of neutral hydrogen has only slightly increased. This suggests that the depletion of gas is not the main reason for the decline in star formation.
Instead, the challenge lies in understanding why it is becoming increasingly difficult to form stars despite the abundance of neutral hydrogen. The researchers propose that changes in how gas moves through the galaxy, rather than the overall quantity of hydrogen, may be the key factor. This discovery could provide new insights into the long-term decline of star formation in the universe.
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