Astronomers have discovered a huge reservoir of cold molecular gas, the direct fuel for star formation, in REBELS-25, a massive, star-forming galaxy. The team, led from Leiden University, focused on REBELS-25, seen when the universe was only about 700 million years old, around 5% of its current age. The research is published in the journal Monthly Notices of the Royal Astronomical Society.

Astronomers use “redshift” to describe this distance, which measures how much the universe’s expansion has stretched a galaxy’s light to redder wavelengths. The higher the redshift, the farther back in time we look. REBELS-25 sits at redshift z = 7.3, deep in the Epoch of Reionization, a key era in which the first stars and galaxies transformed the dark, neutral universe into the universe we see around us today.

Galaxies grow by turning gas into stars, and cold molecular gas is the primary fuel. Until now, astronomers suspected early bright, massive galaxies had huge gas supplies, but no one had directly detected them at these distances.