New Simulations Reveal How Supermassive Black Holes Grew Rapidly in the Early Universe
Using the NSF Very Large Array and ALMA, astronomers have directly detected roughly 100 billion solar masses of cool molecular gas in REBELS-25, a massive star-forming galaxy observed just 700 million years after the Big Bang. The detection, led by Leiden University PhD student Karin Cescon, marks the most distant low-energy carbon monoxide detection ever recorded and provides the first direct measurement of star-forming fuel in such an early galaxy. The finding helps explain how some galaxies grew so large so quickly in the universe's first billion years, and previews the science potential of the planned Next-Generation VLA.
REBELS-25, located at redshift z = 7.31 during the Epoch of Reionization, has been found to harbor an enormous reservoir of cool molecular gas — approximately 100 billion solar masses — confirming long-held suspicions that some early massive galaxies were already primed for intense star formation. The research team, led by Karin Cescon of Leiden University, used deep VLA observations to detect faint radio emission from a low-energy carbon monoxide transition, the most distant such detection ever reported, while ALMA contributed higher-energy CO data, dust measurements, and ionized carbon observations that together constrained the gas's physical conditions and confirmed spatial alignment with other star-formation tracers. A key observational challenge was the cosmic microwave background (CMB), which is significantly warmer and brighter at high redshift, reducing the contrast of cold gas emission and making detection increasingly difficult; the team accounted for this effect to derive the gas mass. The results confirm REBELS-25 is strongly gas-dominated and suggest that ionized carbon emission, one of ALMA's primary tools for studying early galaxies, remains a viable but imperfect tracer of molecular gas at these distances. The study, published in Monthly Notices of the Royal Astronomical Society, provides a direct measurement of the fuel driving rapid mass assembly in the early universe rather than relying on indirect inference. The authors note that REBELS-25 may represent only the tip of the iceberg, and that the planned Next-Generation VLA will be capable of making such measurements ten times faster, enabling surveys of fainter and more distant systems to build a comprehensive picture of how the first galaxies gathered their fuel.
What's missing
The study is based on a single galaxy (REBELS-25), so it is unclear how representative this system is of the broader early-galaxy population. Additionally, the derived gas mass depends on assumptions about CO excitation conditions and the CO-to-H₂ conversion factor, both of which carry significant uncertainties at high redshift and are not fully constrained by current data.
What different sources said
- arXiv astro-phCenter
From nuclear star clusters to Little Red Dots: black hole growth, mergers, and tidal disruptions
- Phys.orgCenter
Cosmic dawn fuel discovery unlocks early galaxy growth secrets
- ALMA ObservatoryCenter
ALMA and VLA Reveal a Vast Reservoir of Star-Forming Fuel in a Galaxy Near Cosmic Dawn
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