In the galaxy NGC 4151, located approximately 50 million light-years away, the XRISM X-ray telescope has achieved a major breakthrough by successfully isolating the powerful winds from a supermassive black hole into distinct velocity components for the first time. These winds drive gas out of the galactic center and suppress star formation, providing an explanation for a long-standing mystery: why the most massive galaxies contain far fewer stars than current models predict.
A research team led by Xin Xiang of the University of Michigan analyzed five sets of observations conducted between 2023 and 2024. Spectra captured by XRISM's instruments revealed that these winds are composed of three distinct layers: slow "warm absorbers" traveling at 100–1,000 km/s, high-speed streams reaching 1,000–10,000 km/s, and ultra-fast outflows accelerating up to 100,000 km/s—nearly one-third the speed of light. In total, the spectra identified up to six layers of absorbing gas, highlighting the highly structured nature of these celestial flows.
These outflows transport significant amounts of the gas necessary for the birth of new stars. In giant galaxies, this mechanism results in a noticeable stellar deficit relative to theoretical predictions. Furthermore, the energy carried by these gas clumps exceeds the threshold required to physically sweep star-forming material out of the galaxy's central regions.
XRISM's observations have enabled scientists to link hard X-ray flares to wind acceleration for the first time, confirming a magnetocentrifugal launch mechanism. With a resolution of approximately 5 electron-volts, XRISM is roughly ten times more powerful than its predecessors, Chandra and XMM-Newton, allowing it to resolve fine spectral details in the critical iron K-edge range where fast-wind signatures are found. These findings were published in the Astrophysical Journal Letters in July 2025 and featured in a presentation at the 248th meeting of the American Astronomical Society in Pasadena in June 2026.
The results illustrate how energy from black hole accretion regulates the evolution of an entire galaxy by limiting the growth of stellar populations in its core, ultimately explaining the scarcity of stars in the universe's largest galaxies.
