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.