XRISM observations show that winds from a supermassive black hole consist of bullet-like clumps. Astronomers previously assumed that the wind material would be smooth and continuous. The energy carried by the gas bullets is over 1,000 times greater than that of regular galaxy-scale winds, suggesting a much stronger impact on the environment. Publication in Nature by an international team of astronomers including Elisa Costantini, Liyi Gu and Aurora Simionescu from SRON.
co-evolution
It is widely believed that every galaxy harbors a black hole of several millions solar masses at its center. Over cosmic time, these black holes and their host galaxies are thought to have evolved together in a tightly linked process. Yet, because of the vast difference in their size and mass, the exact mechanisms behind this interaction remain unclear.
A crucial clue in solving this puzzle lies in the powerful gas flows—known as “outflows” or “winds”—from the regions around black holes. These winds are believed to influence coevolution in two major ways: by regulating the growth of black holes through feedback that limits the inflow of matter, and by injecting vast amounts of energy into their host galaxies, potentially shutting down star formation.
The impact of these winds depends heavily on the amount of energy they carry. To estimate this energy accurately, researchers must first determine the wind’s structure and shape of the wind in detail—something that has remained beyond the reach of previous telescopes.
Observation Results
In March 2024, the research team observed the supermassive black hole PDS 456, located about 2 billion light-years from Earth, using the X-Ray Imaging and Spectroscopy Mission (XRISM). With XRISM’s onboard soft X-ray spectrometer Resolve—to which SRON contributed the filter wheel, including calibration sources—they obtained X-ray spectra that revealed for the first time complex absorption line structures (Figure 2). With previous telescopes, these features had appeared as a single, broad absorption line.
This detailed absorption spectrum reveals at least five distinct components of gas within the black hole’s outflow, each traveling at 20–30% the speed of light (roughly 200 to 300 million km/h). These findings suggest that the wind is not smooth, as previously assumed, but has a clumpy, bullet-like structure, with many discrete high-velocity components.
In addition to the absorption features, XRISM also detected emission lines (Figure 3) originating from the wind. These X-rays are emitted by gas moving both toward and away from Earth. Due to the Doppler effect, this motion broadens the emission lines. Moreover, the strength of the emission lines reflects the total gas content in the wind. The observed line intensities indicate that the outflow is expanding nearly isotropically—in all directions.
Considering this newly revealed picture of a “bullet-like wind,” the research team estimated the gas amount and kinetic energy involved. Their findings show that the wind ejects material at a rate of 60 to 300 solar masses per year, with an energy output more than 1,000 times greater than that of previously observed galactic-scale winds. Previously, it was thought that high-speed winds near black holes transferred all of their energy to large-scale galactic winds, thereby influencing galaxy growth and star formation. However, the new results suggest otherwise: much of the wind’s energy is not transferred outward but instead may be released in bursts—such as so-called geysers—or escape through gaps in surrounding interstellar gas.
Publication
XRISM collaboration, ‘Structured ionized winds shooting out from a quasar at relativistic speeds‘, Nature