In recent years, ALMA observations have shown that massive dense clumps are often composed of many lower-mass dense cores. These dense cores are located in close proximity to one another, but they differ in mass and evolutionary stage, and they also exhibit different physicochemical properties. In the past, low-resolution observations could only obtain the overall properties of massive dense clumps and could not resolve the dense cores within them, their physicochemical properties, or their evolutionary states.

Recently, A. G. TEGEGNE from Ethiopia(CAS–ANSO Fellowship winner), a doctoral student of the star formation and evolution group at the Xinjiang Astronomical Observatory of the Chinese Academy of Sciences, under the supervision of Professor Jarken Esimbek and Andrey M. Sobolev, used ALMA telescope data to study the massive star-forming region G40.282−0.219 and identified three dense corescowithin it, analyzing their physicochemical properties and relative evolutionary states from multiple aspects. The related results have been published in The Astrophysical Journal(1011:33,2026).

G40.282−0.219 is located at a distance of about 3.4 kpc from Earth, and previous low-resolution observations showed that it is a massive young stellar object. Using ALMA data observed at 1.3 mm band, the team resolved it into three dense cores located within the same parental clump: MM1, MM2, and MM3 (see Figure 1).

The study found that MM1 has the largest mass, about 24.6 M_⊙, but has the fewest detected molecular spectral lines, and no associated outflows or masers were detected. MM2 has a mass of about 8.4 M_⊙ and drives a powerful outflow, with its silicon monoxide (SiO) jet having a velocity of about 25 km/s (see Figure 2). MM3 has the smallest mass, about 5.2 M_⊙, yet has the highest dust temperature and the richest variety of molecules, and hosts a 6.7 GHz Class II methanol maser. Therefore, an evolutionary sequence exists within G40.282−0.219, from the youngest MM1 to the most evolved MM3.

The results demonstrate that only by comprehensively considering multiple factors—such as mass, density, temperature and other physical properties, the presence or absence of outflows and jets, the richness of molecular spectral lines, and the types of detected masers—can the evolutionary stages of dense cores in massive star-forming regions be determined more accurately.

This research was supported by the National Key R&D Program, the National Natural Science Foundation of China, and other projects.

Figure 1. (Figure 1 in paper): The G40.282−0.219 region seen by Spitzer (a), the three compact cores resolved by ALMA at 1.3 mm (b), and the methanol masers concentrated around MM3 (c).

Figure 2. (Figure 7 in paper): Molecular gas in G40.282−0.219, traced by SiO, SO, H₂CO, and CH₃OH. Blue and red contours mark the bipolar SiO outflow driven by MM2, and yellow markers show the positions of the three cores.