Astronomers Detect Star-Forming Fuel in a Galaxy 13 Billion Light-Years Away

When the universe was barely 700 million years old—like 5% of its current age— a distant galaxy called REBELS-25 was already holding this colossal kind of reservoir of cold gas, the basic fuel for making stars, you know? A fresh study straight up detected gas for the first time at those cosmic distances, and it gives a real clue to astronomy’s most persistent question: how did early galaxies grow so fast, in the first place?

Carbon Monoxide from 13 Billion Years Ago

Published in Monthly Notices of the Royal Astronomical Society, the study was led by Karin Cescon at Leiden University. Her team used the NSF Very Large Array and ALMA, spending roughly 40 hours hunting faint carbon monoxide signals in REBELS-25, a galaxy at redshift z=7.31 in the Epoch of Reionization. Their CO(3-2) detection is the most distant low-energy CO line ever recorded. Combining VLA and ALMA data, they estimated the galaxy’s molecular gas mass at approximately 100 billion solar masses and a gas fraction of ~95%.

Fuel-Loaded Galaxies and the Road Ahead

A gas fraction of ~95% means nearly all of REBELS-25’s mass was still unprocessed gas, confirming that some early galaxies entered their star-forming prime already loaded with material. Until now, astronomers could only infer such gas supplies indirectly; this direct detection changes what is measurable at cosmic dawn. At this distance, the cosmic microwave background — relic radiation from the Big Bang — acts as a bright backdrop suppressing CO signals, making detection especially challenging. The planned Next-Generation VLA (ngVLA) will make such measurements ten times faster, letting scientists map how entire populations of early galaxies fueled their rapid growth.