Free Astronomy Magazine September-October 2026

41 T he Orion Nebula is perhaps the best known nebula, yet new dis- coveries continue to emerge from observations across all wavelengths of the electromagnetic spectrum. Long known to be a region of active star for- mation, astronomers using the U.S. Na- tional Science Foundation Very Large Array (NSF VLA) have resolved the emis- sion from neutral atomic hydrogen that elucidates how the young stars in Orion are shaping their surrounding neigh- borhood. A team of astronomers led by Juan D. Soler of the University of Vienna used the NSF VLA, operated by the U.S. Na- tional Science Foundation’s National Radio Astronomy Observatories (NSF NRAO), to obtain high-resolution obser- vations of the emission of neutral hy- drogen (HI) atoms, which is detected by a faint radio emission at a wavelength of 21 centimeters. Mapping that emis- sion at high angular resolution is chal- lenging, but the NSF VLA’s interfero- metric design makes it possible to re- solve the structure of nearby star-form- ing regions.The NSF VLA, therefore, proved to be the best possible instru- ment for the task, Soler explains. “The NSF VLA is a very unique instrument. It is fundamental, offering the best reso- lution that we can get in HI from the northern hemisphere. We cannot do this with any other instrument.” When Soler and his team looked deep within the Orion Nebula, they focused on a previously identified expanding bubble formed by young stars. These past observations used tracers such as CII as a proxy for the hydrogen and of- fered an estimate of the mass associ- ated with star formation. Because Soler’s team was able to ob- serve the HI directly, their data provided a more direct estimate of the bubble’s mass,improving measurements by a fac- tor of ten. “Measuring mass is funda- mental, − Soler says − because it tells us how efficiently these newly formed stars shape their environment with wind and radiation.” Furthermore, the data obtained by Soler’s team also map the neutral atomic hydrogen in the vast molecular clouds within the Orion Nebula. Soler describes this interrelationship: “Talk- ing about molecular clouds without talking about HI, is like talking about is- lands without ever mentioning the sea. It turns out that as we’re resolving the sea, we’re finding phenomena like this bubble that are shaping and connecting those molecular clouds. We imagine them as separate objects, not as if they were islands, completely isolated; in fairness, they’re more like archipela- gos.” These results, published in Astronomy & Astrophysics , are the first within a larger project called Neutral Atomic Hydrogen in the Solar Neighborhood (NeAtHood), which aims to continue observing other nearby molecular clouds within star- forming regions visible from the north- ern hemisphere to produce arcminute- resolution HI maps. Soler looks to the possibility of future observations both within this program and beyond, say- ing, “[The bubble] is the kind of thing that should be there, but we were not expecting to see this so clearly. So now I wonder, what other surprises are hid- ing in the data? And in the future, the Next-Generation VLA (ngVLA) is going to target even more distant regions in the Milky Way.” R adio emission from neutral hydrogen atoms in the direction of the Orion Nebula, the most nearby regions of high- mass star formation. The red colors show the 21-cm emission from hydrogen, re- solved for the first time at this level of detail by observations from the Neutral Atomic Hydrogen in the Solar Neighbor- hood (NeAtHood) project, led by Juan Diego Soler from the University of Vi- enna. The cyan colors show the emission from warm interstellar dust in near-in- frared light. [Juan D. Soler, University of Vienna, with data from the NSF NRAO NSF VLA and NASA’s Wide-field Infrared Survey Explorer (WISE)] !