The universe has plenty of hydrogen. So why is star formation collapsing?
Astronomers have discovered a mismatch between the sharp decline in star formation over the last 4.5 billion years and the relatively stable supply of neutral atomic hydrogen. This suggests that the depletion of cold gas is not the sole reason for the universe's slowing star production.
Why it matters
This finding challenges existing models of galaxy evolution and forces scientists to rethink the mechanisms behind star formation.
The universe is producing fewer stellar "babies." Over the past 4.5 billion years, the rate at which new stars form has fallen to less than half its previous level. Yet the supply of one of the most important types of "fuel" for star formation has changed surprisingly little.
That finding comes from an international research team led by scientists from the Chinese Academy of Sciences (CAS), working with the Dark Energy Spectroscopic Instrument (DESI) project. Using China's Five hundred meter Aperture Spherical radio Telescope (FAST), the researchers made precise measurements of cosmic neutral atomic hydrogen across the past 4.5 billion years.
Their results show a striking mismatch. Star formation has declined sharply, while the amount of neutral atomic hydrogen (HI), an important reservoir of gas within galaxies, has decreased only modestly.
The findings were published online in Nature Astronomy on Sept. 1.
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