The data from the NASA and ESA X-ray Imaging and Spectroscopy Mission (XRISM) has discovered unexpected disparities between two different types of cosmic winds, challenging how scientists believed them to form and change.
Wind originating in the disk surrounding the neutron star GX13+1 was significantly denser than that generated from material around a supermassive black hole. The resulting hypothesis proposed in the new research may have significant ramifications for how we understand the forces shaping galaxies.
Observing Cosmic Wind
The observation comes from XRISM’s Resolve instrument viewing GX13+1’s bright X-rays emitting out of the star’s accretion disk during a February 25, 2024, event. Composed of hot matter, the accretion disc is spiraling toward the star’s surface, eventually making direct contact. Events such as these generate power outflows, affecting the surrounding environments, but the exact mechanism of how this occurs remains a mystery.
That mystery is why XRISM was targeting GX13+1 with its Resolve instrument. Researchers hoped to discover new details about incoming X-ray photons, which may shed some light on the outflows.
“When we first saw the wealth of details in the data, we felt we were witnessing a game-changing result,” said co-author Matteo Guainazzi, ESA XRISM project scientist. “For many of us, it was the realisation of a dream that we had chased for decades.”
Effects on Star Formation
Cosmic winds can have tremendous effects on the universe around them, such as collapsing giant molecular clouds into stars, or having the opposite effect, and halting star formation by blowing those clouds into dispersal. Like their multiplicity of effects, cosmic winds are also generated from more than one source, including supermassive black holes.
Despite a lack of understanding of how these winds form, researchers suspected that black hole and star-born varieties would similarly be produced. GX13+1 made a perfect study subject as it was much closer than any supermassive black hole, allowing for a clearer view. While being so close made the star extremely bright, its luminosity unexpectedly peaked—possibly even beyond the Eddington limit—just days before the observation was scheduled to take place.
The Eddington limit describes the theoretical maximum of how bright a neutron star or black hole can become from energy released by infalling matter, before reaching a point where the energy is so intense that it would transform all of the infalling matter into cosmic wind.
“We could not have scheduled this if we had tried,” said co-author Chris Done of Durham University. “The system went from about half its maximum radiation output to something much more intense, creating a wind that was thicker than we’d ever seen before.”
The NASA and ESA collaboration, XRISM, collected the unexpected data. Credit: ESA
An Unexpected Result
Despite the immense power of the event occurring around GX13+1, the wind generated by it was only traveling at one million kilometers per hour. This made the wind’s speed far slower than the more than 200 million kilometers per hour that cosmic winds from supermassive black holes near the Eddington limit can travel.
“It is still a surprise to me how ‘slow’ this wind is,” Done said, “as well as how thick it is. It’s like looking at the Sun through a bank of fog rolling towards us. Everything goes dimmer when the fog is thick.”
Beyond the speed, prior XRISM readings of a supermassive black hole-generated wind were much more choppy than the smooth breeze coming off of GX13+1.
“The winds were utterly different, but they’re from systems which are about the same in terms of the Eddington limit,” Done said. “So if these winds really are just powered by radiation pressure, why are they different?”
Exploring Cosmic Wind
Currently, the team is eying a possible explanation for the difference between supermassive black hole accretion disks and those around neutron stars. Supermassive black holes have lower temperature disks; despite being more luminous, their enormous size spreads their energy thin. As a result, supermassive black hole disks typically project weaker ultraviolet light, rather than more powerful X-rays. While it may be weaker than X-rays, ultraviolet light still interacts with matter much more easily, which may be leading to the faster winds.
“The unprecedented resolution of XRISM allows us to investigate these objects – and many more –in far greater detail, paving the way for the next-generation, high-resolution X-ray telescope such as NewAthena,” said Camille Diez, an ESA Research Fellow with the XRISM collaboration study team who produced the new research.
If eventually proven, the disparity between ultraviolet and X-ray-induced cosmic winds may lead to a dramatic reappraisal of how energy and matter interact in the universe, which drives some of the most powerful galaxy-shaping mechanisms known to astrophysicists.
The paper, “Stratified Wind from a Super-Eddington X-ray Binary is Slower than Expected,” appeared in Nature on September 17, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.