Free Astronomy Magazine November-December 2025

17 NOVEMBER-DECEMBER 2025 ASTRO PUBLISHING W ebb’s image of the enormous stellar jet in Sh2-284 provides evidence that protostellar jets scale with the mass of their parent stars—the more mas- sive the stellar engine driving the plasma, the larger the resulting jet. [Image: NASA, ESA, CSA, STScI, Yu Cheng (NAOJ); Image Processing: J. DePasquale (STScI)] away in the outer reaches of our galaxy. The Webb discovery was serendipitous. “We didn’t really know there was a massive star with this kind of super-jet out there be- fore the observation. Such a spec- tacular outflow of molecular hy- drogen from a massive star is rare in other regions of our galaxy,” said lead author Yu Cheng of the Na- tional Astronomical Observatory of Japan. This unique class of stellar fireworks are highly collimated jets of plasma shooting out from newly forming stars. Such jetted outflows are a star’s spectacular “birth an- nouncement” to the universe. Some of the infalling gas building up around the central star is blasted along the star’s spin axis, likely under the influence of magnetic fields. Today, while hundreds of pro- tostellar jets have been observed, these are mainly from low-mass stars. These spindle-like jets offer clues into the nature of newly form- ing stars. The energetics, narrow- ness, and evolutionary time scales of protostellar jets all serve to con- strain models of the environment and physical properties of the young star powering the outflow. “I was really surprised at the order, symmetry, and size of the jet when we first looked at it,” said co-author Jonathan Tan of the University of Virginia in Charlottesville and Chalmers University of Technology in Gothenburg, Sweden. Its detec- tion offers evidence that protostel- lar jets must scale up with the mass of the star powering them. The more massive the stellar engine propelling the plasma, the larger the gusher’s size. The jet’s detailed filamentary structure, captured by Webb’s crisp resolution in infrared light, is evidence the jet is plowing into interstellar dust and gas. This creates separate knots, bow shocks, and linear chains. The tips of the jet, lying in opposite directions, encap- sulate the history of the star’s for- mation. “Originally the material was close into the star, but over 100,000 years the tips were propagating out, and then the stuff behind is a younger outflow,” said Tan. At nearly twice the distance from the galactic center as our Sun, the host proto-cluster that’s home to the vo- racious jet is on the periphery of our Milky Way galaxy. Within the clus- ter, a few hundred stars are still forming. Being in the galactic hin- terlands means the stars are defi- cient in heavier elements beyond hydrogen and helium. This is meas- ured as metallicity, which gradually increases over cosmic time as each passing stellar generation expels end products of nuclear fusion through winds and supernovae. The low metallicity of Sh2-284 is a reflec- tion of its relatively pristine nature, making it a local analog for the en- vironments in the early universe that were also deficient in heavier elements. “Massive stars, like the one found inside this cluster, have very important influences on the evolution of galaxies. Our discovery is shedding light on the formation mechanism of massive stars in low metallicity environments, so we can use this massive star as a laboratory to study what was going on in ear- lier cosmic history,” said Cheng. Stellar jets, which are powered by the gravitational energy released as a star grows in mass, encode the formation history of the protostar. “Webb’s new images are telling us that the formation of massive stars