[DSRP Evidence](https://dsrpevidence.org/)

# Weak evolution of cosmic atomic hydrogen over the past 4.5 billion years

## Details

**Authors** Zhang et al.

**Year** 2026

**Publisher** Nature Astronomy

**Discipline** Astronomy

[Read it at the publisher](https://doi.org/10.1038/s41550-026-02965-9) 
10.1038/s41550-026-02965-9

## In authors' words

### What they found (results)

Analyzing about 2.5 million galaxies using FAST and DESI data, the team found star formation was roughly 2.5 times higher 4.5 billion years ago while atomic hydrogen reservoirs were only about 1.4 times larger, pointing to declining conversion efficiency from atomic to molecular hydrogen rather than a shrinking gas supply.

## Commentary

### In short

A whole system's output (galaxy-wide star formation) is governed by an intervening relationship — the efficiency of converting one part (atomic gas) into the form actually usable (molecular gas) — rather than following directly from that part's abundance.

**Patterns it shows** S, R

**Added** 2026-09-07

**How to cite this** Zhang et al. (2026). Weak evolution of cosmic atomic hydrogen over the past 4.5 billion years. Nature Astronomy.