Free Astronomy Magazine September-October 2026

24 SEPTEMBER-OCTOBER 2026 ASTRO PUBLISHING T his illustration traces the Universe’s evolution from the Big Bang to the present day, highlighting REBELS-25, a very distant galaxy seen during the Epoch of Reionization 13 billion years ago. New deep observations with the NSF VLA and ALMA reveal that REBELS-25 already had an enormous reservoir of cool molecular gas—the direct fuel for star formation—when the Universe was just 700 million years old. [ALMA Observatory] by modeling of both the CO and dust emission. ALMA played a cru- cial role in completing the picture. Its observations detected higher-en- ergy carbon monoxide emission and provided measurements of dust and ionized carbon, together revealing the gas’s physical conditions and confirming that the CO emission lines up spatially with other star-for- mation tracers. The results confirm that REBELS-25 is strongly gas-dom- inated, with a reservoir large enough to sustain vigorous star for- mation. They also suggest that ion- ized carbon emission, one of ALMA’s most powerful tools for studying early galaxies, remains a viable – if imperfect – tracer of molecular gas at these distances. “This NSF VLA detection is an excit- ing sneak peek of what’s to come with the ngVLA,” noted Karin’s PhD advisor, Professor Jacqueline Hodge. “The ngVLA will allow us to find and study cool gas in many more young galaxies, including those at even earlier times. This will be crucial for understanding how the first galaxies formed and grew.” The discovery helps explain how some early galax- ies grew so large, so fast. The direct confirmation of such a massive gas reservoir – assembled when the Uni- verse was still in its infancy – places REBELS-25 among the most inform- ative laboratories for studying how galaxies built up their ordinary mat- ter, formed stars, and enriched the chemical content of their interstellar medium during the first billion years of cosmic history. Together, ALMA and current and future radio facili- ties are opening a new window onto the fuel supply of the earliest galaxies. Expanding the sample of galaxies with these kinds of meas- urements at z>7 will be essential for understanding how efficiently the first galaxies formed stars – and ulti- mately, how the Universe came to look the way it does today. !