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 billion years ago, while neutral hydrogen levels were only about 1.4 times higher. The universe has plenty of hydrogen. So why is star formation collapsing.

Science News from research organizations The universe has plenty of hydrogen. " 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. Star formation has declined sharply, while the amount of neutral atomic hydrogen (HI), an important reservoir of gas within galaxies, has decreased only modestly.