When the universe was merely 700 million years old, equivalent to roughly 5 percent of its current age, the distant galaxy REBELS-25 already contained an enormous reservoir of cold gas that serves as the essential fuel for star formation. A recent investigation achieved the first direct detection of molecular gas at such extreme cosmic distances, providing fresh insight into how early galaxies achieved rapid growth.

Carbon Monoxide from 13 Billion Years Ago

The findings, published in Monthly Notices of the Royal Astronomical Society, were led by Karin Cescon at Leiden University. The team employed the NSF Very Large Array together with ALMA, devoting about 40 hours to the search for faint carbon monoxide signals from REBELS-25 at redshift z=7.31 during the Epoch of Reionization. Their CO(3-2) detection marks the most distant low-energy CO line recorded so far. Integration of VLA and ALMA measurements yielded a molecular gas mass of approximately 100 billion solar masses and a gas fraction near 95 percent.

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Fuel-Loaded Galaxies and the Road Ahead

The 95 percent gas fraction shows that nearly all of REBELS-25 consisted of unprocessed material, confirming that select early galaxies entered peak star-forming periods already rich in fuel. Prior estimates of such supplies relied on indirect methods, yet this direct measurement expands observational capabilities at cosmic dawn. At this distance the cosmic microwave background acts as an intense backdrop that weakens CO signals and heightens detection difficulty. The planned Next-Generation VLA will increase the speed of comparable observations by a factor of ten, allowing detailed mapping of how entire populations of early galaxies sustained their swift development.