Recently, the research groups of Feng Yuan and Suoqing Ji from the Department of Physics and the Center for Astronomy and Astrophysics at Fudan University have made a breakthrough in the study of gas evolution in galaxy clusters. The related results have been published in the international academic journal Science Advances.
Galaxy clusters are the largest gravitationally bound systems in the universe, and they are filled with hot gas. Theoretically, this gas continuously radiates energy and gradually cools, forming cold gas and triggering star formation—a process known as a cooling flow. However, observations show that the actual cold gas content and star formation rates are significantly lower than theoretical expectations; this discrepancy is the cooling flow problem.
It is now widely believed that feedback from the supermassive black hole at the center of galaxy clusters (i.e., active galactic nuclei, AGN) plays a key role in suppressing cooling flows. During accretion of matter, the black hole releases energy in the form of radiation, jets, and winds into the surrounding medium, thereby affecting the thermal state of the gas. However, previous AGN feedback models were rather phenomenological, with many free parameters, and some parameters deviated considerably from theoretical or observational constraints. In addition, such models generally did not include AGN winds. As a result, even by tuning various parameters, the models could not fully resolve the cooling flow problem.
In this study, the authors employed the numerical simulation framework MACER (Fig. 1), which has been continuously developed by the group in recent years for studying AGN feedback on galactic scales, to perform hydrodynamic simulations of a Perseus-like galaxy cluster system. Compared with previous models, MACER has a more solid physical foundation: 1) the black hole accretion rate is determined much more accurately; 2) physically self-consistent jets and winds are both included; 3) the physical properties of jets and winds are not determined by free parameters but are based on theoretical studies and observational results of small-scale accretion and jets.
Figure 1: The interaction between jets and winds launched from the central black hole in the galaxy cluster triggers Kelvin–Helmholtz instability, which generates strong turbulence. The dissipation of turbulent energy converts the kinetic energy of jets and winds into thermal energy of the intracluster gas, successfully suppressing the cooling flow in the cluster. Taken from He et al., Sci. Adv., aed6394 (2026), Figure 1.
Simulation results show that when both jets and winds are considered, their interaction can excite strong turbulence in the core region of the cluster, enhancing the efficiency of energy transfer from the AGN to the surrounding gas. Under this mechanism, the model effectively suppresses excessive cooling of the gas, and successfully reproduces the observed cold gas mass, star formation rate, black hole mass evolution (Fig. 2), and gas thermodynamic profiles (Fig. 3), with overall results consistent with observations.
Figure 2: Evolution of key physical quantities over time in three models and comparison with observations. Top panel: star formation rate (SFR). The black dashed line and gray shaded region mark the star formation rate of NGC 1275 and its 68% confidence interval, respectively. Second panel: cold gas mass. The gray band indicates the observed molecular gas mass in Perseus. The observed values of star formation rate and cold gas mass represent upper limits for a Perseus-like cluster. Third panel: AGN thermal luminosity in units of Eddington luminosity. Fourth panel: black hole mass and Eddington luminosity. Bottom panel: mass-flow-weighted outer boundary of the accretion flow. Only the JetWind model successfully reproduces the observed ranges of cold gas mass, star formation rate, and black hole mass. Taken from He et al., Sci. Adv., aed6394 (2026), Figure 2.
Figure 3: Radial distribution of entropy in the intracluster medium and comparison with observations. The shaded regions represent the 10th to 90th percentile distributions of the simulation profiles. The black dashed line and red band denote the median and one-sigma profile from the ACCEPT galaxy cluster sample observations, respectively. The dash-dotted and dotted lines represent different power-law fits for the outer and inner regions of the cluster, respectively. Only the JetWind model reproduces the observed entropy distribution for most of its evolution time. Taken from He et al., Sci. Adv., aed6394 (2026), Figure 3.
This work provides new insights into the thermodynamic evolution of gas in galaxy clusters and the AGN feedback mechanism, and also offers a reference for related numerical simulation studies.
The study was led by the research groups of Yuan Feng and Ji Suoqing at Fudan University. Yuan Feng and Ji Suoqing are co-corresponding authors, and the first author is a graduate student they supervised at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences. Collaborators include Professor Yuan Li from the University of Massachusetts Amherst, Professor Xu Haiguang from Shanghai Jiao Tong University, and the research group of Professor Sun Ming from the University of Alabama. The work was supported by projects including the Major Program of the National Natural Science Foundation of China.
Paper link:
https://www.science.org/doi/10.1126/sciadv.aed6394
MACER project homepage:
https://macer-project.github.io/