Astronomers have captured a striking image of a cold stream of molecular gas flowing outside a distant galaxy cluster. The finding, reported in Science, adds a crucial piece to the long-standing question of how galaxies sustain star formation by drawing in material from their surroundings. For years, researchers believed that cool gas streams drift through intergalactic space and occasionally plunge into galaxies, feeding new stars. Yet proving this idea proved difficult because the gas is so cold that its energy output is faint and falls outside the most observable wavelengths.
In a recent study led by Bjorn Emonts and colleagues, the presence of a feeding stream toward the galaxy known as 4C 41.17 has been detected. The team used the Atacama Large Millimeter/submillimeter Array, commonly called ALMA, positioned in the high desert of Chile. The detected stream is predominantly made up of carbon-rich material and stretches over more than half a million light-years. While the discovery confirms a gas supply channel, scientists caution that estimates of the stream’s exact composition remain uncertain, and there is not yet a clear picture of the gas origin or its precise path toward the galaxy.
Looking ahead, the researchers plan further observations with the Very Large Array, a radio telescope facility that could, in theory, reveal traces of carbon monoxide within the predicted flow. The team also aims to identify the telltale features that would allow future detections of similar streams, with the objective of building a comprehensive model for how such gas accumulates and fuels star formation in galaxies over cosmic time. In addition to refining measurements, the work seeks to map the conditions under which cold gas can survive the journey through intergalactic space and reach galactic disks, a step toward understanding how massive galaxies grow and evolve.