Free Astronomy Magazine July-August 2025

17 ASTRO PUBLISHING “Our observations provide direct ev- idence that massive stars can form through disk-mediated accretion up to tens of solar masses,” said Dr. Al- berto Sanna, lead author of the study. “The NSF VLA’s unparalleled radio sensitivity allowed us to re- solve features on scales on the order of 100 AU only, offering unprece- dented insights into this process.” The team also compared their obser- vations with state-of-the-art simu- lations of massive star formation. “The results aligned closely with theoretical predictions, showing that ammonia gas near HW2 is col- lapsing almost at free-fall speeds while rotating at sub-Keplerian ve- locities—a balance dictated by grav- ity and centrifugal forces,” said Prof. André Oliva, who performed the detailed simulations. Interestingly, the study uncovered asymmetries in the disk’s structure and turbulence, suggesting that ex- ternal streams of gas—known as “streamers”—may be delivering fresh material to one side of the disk. Such streamers have been ob- served in other star-forming regions and may play a crucial role in replen- ishing accretion disks around mas- sive stars. This discovery resolves decades of debate over whether HW2, and protostars alike, can form accretion disks able to sustain their rapid growth. It also reinforces the idea that similar physical mecha- nisms govern star formation across a wide range of stellar masses. “HW2 has been known for more than 40 years by now and still in- spires new generations of as- tronomers,” said Prof. José María Torrelles, who conducted some pivotal observations of HW2 in the late ‘90s. The findings were made possible by high-sensitivity NSF VLA observations conducted at centime- ter wavelengths in 2019. The re- searchers targeted specific ammonia transitions that are excited at tem- peratures above 100 Kelvin, en- abling them to trace dense and warm gas near HW2. “These results highlight the power of radio interferometry to probe the hidden processes behind the forma- tion of the most influential objects in our Galaxy, − said Dr. Todd Hunter of the NRAO, , − and, in ten years, the next upgraded version of the VLA will make it possible to study circum-stellar ammonia at scales of our Solar system.” This work not only advances our un- derstanding of how massive stars form but also has implications for broader questions about galaxy evo- lution and chemical enrichment in the universe. Massive stars play piv- otal roles as cosmic engines, driving winds and explosions that seed galaxies with heavy elements. JULY-AUGUST 2025 A mmonia gas infalling into accre- tion disk feeding Cepheus A HW2. [NSF/AUI/NSF NRAO/B. Saxton] !