The X-Ray Imaging and Spectroscopy Mission (XRISM) has recorded unusually dense, slow winds from the neutron star system GX13+1, revealing a striking contrast with the ultrafast outflows commonly seen near supermassive black holes operating at similar radiative conditions. The result challenges prevailing models of radiation-driven winds from accretion discs and offers new insight into how compact objects inject energy and momentum into their surroundings.
What XRISM saw
On 25 February 2024, XRISM’s Resolve instrument observed GX13+1, a bright X-ray binary where material spirals onto a neutron star. Just before the observing window, the system brightened to near or above the Eddington limit, a regime where radiation pressure can push infalling matter outward. Resolve’s high spectral resolution captured a wind that was exceptionally thick yet moving at roughly 1 million km/h—fast by terrestrial standards but far slower than the 20–30% of light speed often measured near supermassive black holes under comparable conditions.
In addition to its lower velocity, the outflow from GX13+1 appeared smooth rather than highly clumpy, marking another clear difference from the ultrafast, structured winds previously identified near active galactic nuclei at the Eddington limit.
A temperature and coupling puzzle
The findings point to the role of accretion disc temperature and the type of radiation driving the flow. Accretion discs around supermassive black holes are larger and cooler, emitting primarily ultraviolet light, which couples efficiently to gas and can accelerate winds more effectively. By contrast, the hotter, X-ray–bright discs in stellar-mass systems like GX13+1 may couple less efficiently, producing slower, denser outflows even when radiation pressure is intense.
Why it matters
Radiation-driven winds regulate how black holes and neutron stars grow and how they influence their environments. In galaxies, this feedback can either trigger star formation by compressing gas or suppress it by heating and dispersing clouds. By contrasting wind properties across mass scales, the GX13+1 observation refines how models link disc emission, radiation coupling, and outflow dynamics—key ingredients for simulations of galaxy evolution.
Mission and instrumentation
XRISM, a mission led by JAXA in partnership with NASA and ESA, launched on 7 September 2023. It carries two instruments: Resolve, an X-ray calorimeter that measures the energy of individual photons with unprecedented resolution, and Xtend, a wide-field X-ray CCD imager. The GX13+1 dataset leverages Resolve’s spectral precision to distinguish ion species, measure gas velocities, and quantify column densities across multiple wind phases.
Key takeaways
- GX13+1 produced an unusually dense, slow wind despite operating near the Eddington limit.
- The outflow was smooth rather than clumpy, contrasting with ultrafast winds seen near supermassive black holes.
- Differences likely stem from disc temperature and radiation type (ultraviolet vs X-rays) and their coupling to gas.
- Results sharpen models of radiation-pressure feedback from compact objects and its role in cosmic evolution.
What’s next
The observation demonstrates XRISM’s capability to dissect multi-phase winds in compact systems and sets the stage for deeper surveys of neutron stars and black holes across accretion states. These measurements pave the way for next-generation, high-resolution X-ray observatories to map wind launching zones and quantify feedback with greater fidelity.
Study: “Multi-phase winds from a super-Eddington X-ray binary are slower than expected,” published by the XRISM collaboration in Nature. Source: ESA: XRISM uncovers a mystery in the cosmic winds of change.
