A recent international collaboration led by researchers from Yunnan University, the Shanghai Astronomical Observatory (Chinese Academy of Sciences), and the National Astronomical Observatory of Japan has unveiled new insights into the fragmentation mechanisms of high-mass star-forming regions. Using the Atacama Large Millimeter/submillimeter Array (ALMA), the team conducted high-resolution observations of an S-shaped massive star-forming region, revealing a multi-scale fragmentation process driven by feedback from ionized regions. The findings provide new observational support for the "clump-fed" model of massive star formation, offering crucial evidence for understanding the dynamic processes of stellar birth. The study has been published in the journal Astronomy & Astrophysics.

The research team focused on IRAS 19074+0752 (I19074), conducting detailed ALMA observations at 1.3 mm with a spatial resolution of approximately 6,000 astronomical units (au). They discovered an elongated S-shaped filament spanning 2.8 parsecs, which resembles a dancing Chinese Loong, composed of a northern segment (Fn) and a southern segment (Fs). Fn is closely associated with a bright infrared HII region, while Fs resides in a relatively quiescent, infrared-dark environment. The team proposed that the S-shaped morphology likely results from the compression and bending of an originally linear filament by the expanding HII region, shedding new light on filament formation and its interaction with the interstellar medium.

The study further revealed a hierarchical fragmentation pattern in I19074, following a "filament → clump → core" sequence. However, Fn and Fs exhibited distinct fragmentation mechanisms. Fn, influenced by the HII region, displayed a "shell-fragmentation" pattern, forming three clumps spaced roughly 1 parsec apart—consistent with the "collect-and-collapse" model driven by ionized gas expansion. In contrast, Fs showed only one clump at the filament's end, aligning with the "end-dominated collapse" mechanism, where gravitational instability triggers localized fragmentation. Notably, within both Fn and Fs, the average spacing between cores was about 0.17 parsecs, explainable by near-spherical Jeans fragmentation, suggesting that small-scale core formation within clumps is largely independent of the large-scale environment. This finding highlights that while filament fragmentation is strongly influenced by external feedback, clump-to-core fragmentation follows universal physical laws—a key insight for future studies.

Additionally, the team identified 26 dense cores in I19074, with masses ranging from 1 to 23 solar masses. Of these, 92% were gravitationally bound, and no clear candidate for a massive starless core was detected. These results support the "clump-fed" model, where cores grow into massive stars by continuously accreting material from their surrounding clumps, providing new observational constraints on high-mass star formation theories.

Figure: Left: The S-shaped structure in the target region I19074, with gray ellipses marking dense cores and green symbols indicating protostars. Scale bars and resolution indicators are shown in the upper-right and lower-right corners. Right: Distribution of core spacings within the S-shaped structure, where green ellipses represent clumps and blue dots denote cores.

The study’s first authors are Guo Yongqi, a Master’s student at Yunnan University’s School of Physics and Astronomy, and Dr. Liu Hongli (corresponding author), an associated professor at the same institution. Dr. Lü Xing from Shanghai Astronomical Observatory and Dr. Cheng Yu from the National Astronomical Observatory of Japan served as co-corresponding authors. The collaboration included researchers from mainland China, Taiwan (China), Japan, Mexico, the United States, Germany, and Chile.

Publication Link: https://doi.org/10.1051/0004-6361/202556572

Scientific Contacts:

Liu Hongli (Yunnan University): hongliliu2012@gmail.com

Lü Xing (Shanghai Astronomical Observatory): xinglv.nju@gmail.com

Cheng Yu (National Astronomical Observatory of Japan): ycheng.astro@gmail.com