FAST and DESI: Falling Star Formation Is Not a Simple Fuel Crisis

An international team led by Hong Guo of the Chinese Academy of Sciences used FAST and DESI to measure cosmic neutral hydrogen across about 2.5 million galaxies over the past 4.5 billion years. Star formation fell roughly 2.5-fold while neutral hydrogen density dropped only about 1.4-fold, so the decline is not explained by a lack of fuel.

• Sample covered about 2.5 million galaxies and nearly a third of the sky
• 4.5 billion years ago stars formed about 2.5 times faster than today
• Neutral atomic hydrogen density fell only about 1.4 times
• Researchers point to the baryon cycle, not a simple fuel shortage