Division of Science, NAOJ

ALMA High-Resolution Observations Reveal New Evidence for Bimodal Fragmentation and Multi-Scale Dynamical Mass Accretion in High-Mass Star Formation

For decades, formation of high-mass stars exceeding 8 solar masses has remained one of astronomy’s greatest mysteries. In a recent study published in Astronomy & Astrophysics, a global team of astronomers, including researchers from Yunnan University, Shanghai Astronomical Observatory and Division of Science of NAOJ, has carried out cutting-edge observations toward a “hub-filament system” (HFS) molecular cloud—a cradle of high-mass star formation, and has uncovered stunning new evidence that challenges current theories and illuminates the multi-scale, dynamical  nature of high-mass stellar birth.

Using the world’s most advanced (sub)millimeter interferometer, ALMA, the research team conducted ~3000AU resolution observations at the 1.3mm wavelength toward the HFS I18308 cloud, a high star-forming region with a textbook example of HFS morphologies (left panel, Figure 1).  The team revealed dual fragmentation modes. Two hub-composing filaments (F1 and F2) exhibit a cylinder-like fragmentation mode, with the quasi-periodic core spacings regulated by the turbulence-dominated fragmentation mechanism. In contrast, the central hub clump shows a spherical-like fragmentation mode, with the core spacings regulated by gravity-dominated Jeans fragmentation mechanism. These findings challenge models predicting a single fragmentation mode across all density scales within molecular clouds (e.g., the global gravitational collapse model).

Moreover, the team did not find high-mass prestellar cores surpassing 30 solar masses; and instead all relatively low-mass cores show a systematic increase in mass and density with evolution. These observed facts support a multi-scale accretion scenario: low-mass prestellar cores form via Jeans fragmentation in the hub, collapse into intermediate-mass protostars, and grow into high-mass stars through hierarchical mass accretion from the filaments, hub clump, and cores (right panel, Figure 1).

Article Information

L. M. Zhen, H-L. Liu, X. Lu, Y. Cheng, R. Galván-Madrid, H. B. Liu, P. Sanhueza, T. Liu, D. T. Yang, F. Nakamura, S. H. Jiao, L. Chen, Y. Q. Guo, S. Y. Feng, Q. Zhang, X. C. Liu, K. Wang, Q. L. Gu, Q. Y. Luo, Y. Lin, P. S. Li, S. H. Li, K. Tanaka , A. E. Guzmán, “Hierarchical fragmentation in HFS I18308 observed as part of the INFANT survey”, Astronomy & Astrophysics, 2025, 70, A47.
https://doi.org/10.1051/0004-6361/202554634

Corresponding Authors: Y. Cheng, H-L. Liu, X. Lu