Massive stars form within cold, dense molecular clouds. As gas contracts under gravity, it can readily fragment into many smaller cores. A longstanding question in astronomy is thereforehow massive stars avoid excessive fragmentation of their surrounding material and acquire enough “fuel” to continue growing?

Recently, MENG Dezhao, a PhD student in the star formation and evolution group at the Xinjiang Astronomical Observatory of the Chinese Academy of Sciences (CAS), and collaborators from China and other countries investigated how massive protostars heat their surrounding material using data from the ALMA-QUARKS survey. The study found that intense radiation from protostars can suppress further fragmentation of the surrounding hot molecular cores, thereby creating favorable conditions for massive stars to continue accreting material and growing.

The results have been published in The Astrophysical Journal Supplement Series.

The researchers identified 83 hot molecular cores in 58 massive star-forming regions. They used methyl cyanide as a molecular “thermometer” to map the temperature and density distributions within the hot cores.,andapplied radiative-transfer modeling to estimate the luminosities of the central protostars. The results show that these hot cores generally become cooler with increasing distance from their centers (see Figure 1), indicating that their envelopes are being continuously heated by the embedded protostars.

Further analysis revealed that the more luminous a protostar is, the more resistant its surrounding gas is to fragmentation. The researchers used the thermal Jeans mass to characterize the critical mass required for gravitational fragmentation. On average, the thermal Jeans mass in the sample is approximately twice the mass of the hot-core envelope (see Figure 2). This suggests that protostellar heating acts like a “thermal barrier,” raising the threshold for gas fragmentation and allowing material to remain concentrated in a small number of massive cores rather than being dispersed into numerous low-mass objects.

The researchers also found that more massive molecular clumps tend to host more luminous protostars and consequently experience stronger thermal feedback. These results provide new observational constraints on the coevolution of massive protostars, hot molecular cores, and their parental molecular clumps.

This work was supported by the National Science and Technology Major Project of China, and the National Key R&D Program of China, the National Natural Science Foundation of China.

                                                                                 Figure 1. (Figure 2 in paper): an example of temperature, density and abundance distributions.

                                                                              Figure 2. (Figure 8 in paper): The relation between thermal Jeans mass and luminosity, envelope mass.