GX 301-2 flares have been linked to a dense plume of stellar wind from its massive companion star, according to new space telescope observations that illuminate how an extreme neutron star feeds on nearby material and brightens in X-rays.
The binary system, known as BP Crucis and located about 13,000 light-years away, pairs a blue hypergiant called Wray 977, estimated to be about 60 times the mass of the sun, with a neutron star designated GX 301-2. The neutron star is a pulsar, packing roughly the sun’s mass into a sphere about 20 kilometers across, with an intense magnetic field and rapid spin that produce a sweeping beam of electromagnetic radiation. When that beam points toward Earth, telescopes record a pulse roughly every 11 minutes.
Unlike typical pulsars, GX 301-2 also produces frequent X-ray outbursts that temporarily boost its brightness, a pattern that had lacked a confirmed cause until now.
In a study published Sept. 18 in Science Advances, researchers used the X-ray Imaging and Spectroscopy Mission, or XRISM, operated by NASA and the Japan Aerospace Exploration Agency, to probe BP Crucis in detail. The team found that the neutron star’s outbursts occur when it passes through a concentrated plume of stellar wind plasma emitted by Wray 977.
This marks the first direct detection of this kind of stellar wind material interacting with a neutron star or similar compact remnant, opening new avenues to investigate accretion in extreme environments.
“We’ve never before seen clear indications of wind plasma falling onto a compact object,” said first author Roi Rahin of the University of Maryland, Baltimore County, and NASA’s Goddard Space Flight Center. “We can now test our understanding of these processes in much greater detail.”
GX 301-2 flares mapped to a stellar wind plume
All fusion-powered stars shed radiation and charged particles as stellar wind. The sun’s outflow, the solar wind, can drive auroras at Earth. Far more massive stars such as Wray 977 produce much stronger winds. In this case, the hypergiant appears to vent a single, dense stream of ionized gas moving at about 540,000 kilometers per hour. Researchers suggest the neutron star’s gravity sculpts the outflow into a focused plume.
GX 301-2 orbits Wray 977 every 41.5 days and shows X-ray flares near both its closest and farthest approach, with the brightest at closest approach. This pattern had long hinted that the neutron star was plunging through the wind plume, but confirmation required high-resolution spectroscopy.
During a 16-hour window that coincided with one of the outbursts, XRISM captured detailed X-ray spectra from the system. NASA officials said the data showed rapidly changing emission and absorption features that tracked how the plume ebbed and flowed around the neutron star.
“We could see how the dense stream of plasma acts very close to the neutron star,” said co-author Nazma Islam of the Manipal Centre for Natural Sciences in India, formerly with UMBC and NASA Goddard. “It was clear that these observations were groundbreaking, but at the same time this meant the analysis had to be especially detailed.”
Using the spectra, the team simulated how the plasma falls onto and circulates around the neutron star. When enough material builds up on the surface, it triggers an explosive release that produces the bright X-ray flashes detected from Earth.
Researchers plan to monitor future outbursts with XRISM to further characterize the interaction between GX 301-2 and Wray 977’s wind stream.
“The BP Crucis system is an ideal laboratory for studying wind-fed pulsar accretion,” said Brian Williams, XRISM project scientist at NASA Goddard, adding that XRISM is well suited to advance understanding of these processes.
Citation: Rahin, R., Ballhausen, R., Islam, N., Leutenegger, M. A., Behar, E., Zamora, D., Coley, J., Hell, N., Kallman, T., Lorenz, M., Pradhan, P., Wilms, J., & Zainab, A. (2026). Direct spectroscopic observation of matter falling onto a compact stellar object. Science Advances, 12(38), eaef6686. https://doi.org/10.1126/sciadv.aef6686
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