Astronomers have found evidence that massive stars can form via a classic accretion disk, even in the most extreme environment of our galaxy—the Central Molecular Zone (CMZ)— demonstrating that the disk-driven process works no matter how hostile the surroundings are.

This finding was published in The Astrophysical Journal by researchers from the Shanghai Astronomical Observatory of the Chinese Academy of Sciences.

The CMZ, located approximately 8.3 kiloparsecs from Earth, represents the most extreme environment in the Milky Way. In the study, researchers conducted high-resolution observations of the Galactic Center region using the Atacama Large Millimeter/submillimeter Array, focusing on the early O-type massive protostar G359.44-0.102 and its surrounding Keplerian accretion disk in the Sagittarius C molecular cloud within the CMZ.

The research team analyzed the emission features and spatial distribution of complex organic molecules in this system, revealing the intricate dynamical structure among the inner accretion disk, outer envelope, and gravitationally collapsing accretion flows.

The results reveal a clear chemical differentiation in the molecular emission surrounding this star: nitrogen-bearing molecules are predominantly concentrated in a compact inner region, while oxygen-bearing molecules exhibit a more extended and diffuse distribution.

Meanwhile, by constructing a three-dimensional dynamical model incorporating an inner Keplerian disk and an outer free-fall envelope, the researchers precisely constrained the mass of the central protostar and the structure of the accretion disk. The study further analyzed the efficiency of material transport toward the central star.

In addition, the team identified spiral structures and velocity gradients in both the dust continuum and the molecular line-of-sight velocity field of the disk. Particle trajectory modeling confirmed that these spiral structures are, in fact, accretion streams undergoing gravitational collapse and spiraling inward toward the central protostar.

In the CMZ —a region where the overall star formation efficiency is significantly suppressed due to factors such as extremely high turbulence— massive protostars can still rapidly accumulate mass through the combined action of the accretion disk, envelope, and accretion flows.

This indicates that, at the gravity-dominated accretion disk scale, star formation activity is insensitive to macroscopic large-scale environmental conditions, demonstrating the universality of disk-mediated accretion across different environments in the Milky Way.

According to the researchers, this study enhances our understanding of the accretion mechanisms of massive protostars in extreme environments by providing observational evidence for the mass accumulation process of early O-type stars.

An artist's impression of the accretion disk, envelopen, and streamers surrounding the massive protostar G359.44-0.102. (Image by SHAO)