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A powerful plume of ionized gas from a blue hypergiant is repeatedly lighting up a nearby neutron star, producing bright X-ray outbursts that reach Earth, researchers report. New observations with the XRISM X-ray telescope reveal how the two stars in the BP Crucis system interact and why the compact object flares so often.
What BP Crucis is
BP Crucis is a binary system about 13,000 light-years away. Its primary is the blue hypergiant Wray 977, estimated to be roughly 60 times the mass of the Sun. Its companion is a tiny, ultradense neutron star known as GX 301-2.
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The neutron star packs roughly the Sun’s mass into a sphere only about 12 miles (20 kilometers) across and behaves as a pulsar, spinning and sweeping a beam of electromagnetic radiation — including X-rays — across space. When that beam crosses Earth, telescopes register a pulse roughly every 11 minutes.
Strange, repeated flares
Beyond its regular pulses, GX 301-2 also produces separate, bright X-ray flares at repeated intervals. The neutron star completes an orbit around Wray 977 every 41.5 days, and astronomers had long suspected the flares relate to the star moving through its partner’s wind. Until now, they lacked direct spectroscopic proof.
XRISM caught the culprit
Using the joint NASA–JAXA XRISM mission, scientists observed BP Crucis during a 16-hour window that included one of the neutron star’s flares. The telescope recorded detailed X-ray spectra that showed rapidly changing emission and absorption lines as material flowed past and around GX 301-2.
Those spectral signatures matched a model in which the hypergiant ejects a concentrated plume of ionized gas — a stellar wind moving at roughly 335,000 miles per hour (540,000 km/h) — and the neutron star disturbs and accretes that material as it passes through. When enough plasma accumulates on the compact object’s surface, it triggers the bright X-ray flashes visible from Earth.
First direct detection of wind plasma accretion
According to the study, this is the first time researchers have directly observed stellar wind plasma interacting with a neutron star or a similar compact remnant. “We’ve never before seen clear indications of wind plasma falling onto a compact object,” said study lead 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.”
Co-author Nazma Islam added that the observations were “groundbreaking” and required especially careful analysis to interpret the rapidly changing spectral features.
What comes next
With XRISM’s sensitivity, the team was able to simulate how the plume wraps around the pulsar and how material collects and ignites the flares. The researchers plan additional observations of future flaring events to refine their models of wind-fed accretion in systems like BP Crucis.
“The BP Crucis system is an ideal laboratory for studying wind-fed pulsar accretion,” said XRISM project scientist Brian Williams at NASA Goddard. He described XRISM as “an ideal instrument for advancing our understanding of the processes involved.”
Broader context
All nuclear-burning stars shed particles and radiation in stellar winds; the Sun’s solar wind, for example, helps produce auroras on Earth. But winds from very massive stars can be far stronger and, as XRISM has shown in this case, can form dense, concentrated plumes that dramatically affect nearby compact objects.
Study details
The findings were published Sept. 18 in the journal Science Advances (Rahin et al., 2026) and are based on XRISM X-ray spectroscopy that captured the dynamic interaction between Wray 977’s plume and GX 301-2. Researchers say the result opens a new window onto how extreme stellar winds feed and light up compact remnants.
