Recently, a research team led by the Tianma group, utilizing the Shanghai Tianma 65-meter telescope and Yebes 40-meter telescope, discovered that the turbulence caused by shear-motionof molecular clouds may be the dominant heating mechanism for molecular gas in the Galactic Center. This research was published in the Astrophysical Journal in January 14, 2026, providing new observational and theoretical evidence for studying energy transfer mechanisms in the extreme environments of galactic centers.

The Central Molecular Zone (CMZ) of the Milky Wayis a special region surrounding the supermassive black hole at the galactic center, spanning a radius of approximately 200 to 300 parsecs. It harbors about 5% of the galaxy's molecular gas. Compared to molecular clouds in the galactic disk (typically at temperatures of 10–20 K), the CMZ molecular clouds exhibit significantly higher average temperatures and complex temperature structures. Dominant components include warm gas (50–150 K) and a small fraction of hot molecular gas exceeding 400 K. Notably, the cooling time of hot molecular gas is extremely short(on the order of years), indicating the presence of a continuous and stable heating mechanism in the Galactic Center. However, the nature of this heating mechanism has remained unresolved.

The research team emplyed the Shanghai Tianma 65-meter telescope and the Yebes 40-meter telescopeto observe multiple transition lines of ammonia (NH₃) in the molecular cloud G0.66-0.13 within the CMZ (see Figure 1 (I)). For the first time, the team detected the emission line of the high-energy transition (18, 18) of NH₃ in interstellar space, with an energy level temperature as high as 3100 K. Analysis showed that the high-energy transition lines originate from hot molecular gas exceeding 400 K, and their spatial distribution differs significantly from that of thewarm gas (50~150 K) (see Figure 1 (II)). By comparing the velocity field of warm gas with the spatial distribution of hot gas (see Figure 2), the team found that hot gas is predominantly concentrated at the interfaces between different cloud components.

Figure 1 (I), The spectra of NH₃ (13, 13) - (18, 18) toward positions (a) and (b) in G0.66-0.13. The black lines represent the observations, while the red lines represent the Gaussian fitting result. These spectra were observed with the Yebes 40m telescope. (II), The spatial distribution of NH₃ (13, 13) (contours) overlayed on that of NH₃ (6,6) (color-scale) toward G0.66-0.13. NH₃ (13,13) was mapped with the Yebes 40 m telescope, while the NH₃ (6,6) is mapped with TMRT. The white crosses denote the positions toward which long integration time observations were carried out and rotation diagrams were constructed. The green and red circles in the left corner denote the beamsizes for observations of NH₃ (6, 6) and (13, 13), respectively.

Figure 2 The distribution of integrated intensity of NH₃ (13, 13) (contours) overlayed on intensity-weighted mean velocity map of NH₃ (6, 6) in color scale. The blue line represents the orbit of stream around the gravitational potential center of the Galaxy. The pink curves mark the boundaries of different gas components. The green and red circles in the left corner denote the beamsizes for observations of NH₃ (6, 6) and (13, 13), respectively.

Calculations showed that the intermittent turbulent dissipation model predicted that localized extreme heating due to turbulent dissipation can directly producegas components with temperatures exceeding 400 K (see Figure 3 (a)), thereby explaining the complex temperature stratification of CMZ molecular clouds. This finding indicates that the shear motions between molecular clouds rotate under the gravitational potential of the nuclear star cluster and supermassive black hole may induce turbulence, thereby heating some gas to high temperatures (see Figure 3(b)). This mechanism may be universally applicable to other extreme physical environments in galactic cores.

Figure 3 (a), The cumulative probability of temperature smaller than T in a molecular cloud with different line widths. The results are derived by assuming that the dissipation rate follows log-Poisson distribution, which is consistent with the intermittency turbulence model. The cloud size was assumed to be 5 pc. A pink box is used to highlight the high-temperature fraction predicted by the model. (b), A schematic picture of the proposed scenario on how hot molecular gas was generated in the Galactic center. Cloud A and Cloud B rotate around the Galactic center under the gravitational potential of the nuclear stellar clusters (NSCs) and the supper massive black hole.

The research was conducted jointly by Shanghai Astronomical Observatory, Guangxi University, Tsinghua University, Sun Yat-sen University, Purple Mountain Observatory, Nanjing University, and research institutions from Spain and South Korea. The study was supported by the National Key Research and Development Program of China, the Oriental Talent Plan, and the State Key Laboratory of Radio Astronomy and Technology.