Pulsar Caught Stealing a Giant Star's Wind, and Astronomers Watched It Happen

File Zero | Space Desk | September 19, 2026

Researchers led by Roi Rahin at NASA's Goddard Space Flight Center used the XRISM observatory to directly observe a pulsar capturing stellar wind from a companion star on February 1, 2025, revealing for the first time how compact objects generate powerful X-ray flares in the BP Crucis system, NASA said.

What the researchers found

The target is BP Crucis, a two-star system about 13,000 light-years away in the southern constellation Crux, according to NASA. One star is Wray 977, a blue hypergiant that NASA says is roughly 40 times the mass of the Sun and 60 times its size. A star that large and hot constantly sheds ionized gas into space. Astronomers call that outflow a stellar wind.

The other object in the system is GX 301-2, a neutron star, which NASA describes as the crushed core of a star that exploded long ago as a supernova. NASA says it packs more than the Sun's mass into a ball roughly 12 miles (20 kilometers) across. It rotates every 11 minutes, sweeping an X-ray beam toward Earth with each turn. That rotation pattern is what qualifies it as a pulsar.

Rahin, who is affiliated with both the University of Maryland, Baltimore County and NASA Goddard, said the team had never before seen clear indications of wind plasma falling onto a compact object. A paper describing the findings published Friday in the journal Science Advances.

What XRISM saw

The team pointed the XRISM observatory at BP Crucis on February 1, 2025, and observed it for about 16 hours near the end of one of the system's stronger X-ray flares, according to NASA. XRISM is a Japan-led mission operated jointly with NASA and JAXA, the Japan Aerospace Exploration Agency.

The key instrument was Resolve, a spectrometer jointly developed by NASA and JAXA. It captured highly detailed X-ray spectra showing rapidly changing emission and absorption lines. The absorption lines from highly ionized iron were the telling detail: they appeared shifted to lower energies than they would be in a laboratory setting.

That shift is called a redshift, and it indicates the gas is moving away from the observer, which in this geometry means it is falling toward the pulsar. NASA says the team's analysis puts the plasma's infall speed at around 335,000 mph (540,000 kph).

Rahin said when he first saw the spectra, he had not seen anything like them before. He searched the scientific literature for comparable observations and found none.

How the feeding works

NASA describes the process in three stages, based on what the researchers worked out from the XRISM data.

When the pulsar first enters the dense stream of plasma flowing from Wray 977, it sweeps gas into a thick, turbulent disk around itself. That gas spirals inward, heats up, and emits X-rays, powering the flares. The pulsar's 41.5-day orbit brings it through this stream twice per orbit, near its closest and farthest points from the primary star, and the strongest flares happen closer in, where the stream is denser, according to NASA.

As the pulsar moves deeper into the stream, the disk breaks down. NASA says astronomers think the stream no longer carries enough angular momentum, a measure of rotational force, to keep the disk intact. Once the disk falls apart, plasma drops straight onto the neutron star.

Near the end of the transit, a disk briefly rebuilds, this time spinning in the opposite direction from the first one, because of the way the stream is flowing. Then it too disappears as the pulsar exits. NASA says the full transit through the stream takes about four days.

Co-author Nazma Islam, formerly at UMBC and NASA Goddard and now an assistant professor at Manipal Centre for Natural Sciences in India, said the observations showed how the dense stream of plasma behaves very close to the neutron star. She described the analysis as especially detailed, precisely because the observations were unlike anything seen before.

Brian Williams, the XRISM mission's project scientist at NASA Goddard, called BP Crucis an ideal laboratory for studying wind-fed pulsar accretion, and said XRISM's Resolve spectrometer is well suited to advancing understanding of the processes involved.

Why it matters

Neutron stars and black holes are thought to grow by pulling in, or accreting, material from nearby objects. Theoretical models of that process have existed for decades, but direct observation of the plasma in the act of falling onto a compact object had not been achieved before this, according to NASA. Watching it happen in BP Crucis gives researchers a way to test those models against real measurements rather than inferences.

What the team does not yet know is how representative BP Crucis is of other wind-fed binary systems throughout the galaxy. That question is not addressed in the material NASA has published.

NASA's full account of the findings is at nasa.gov/xrism.

Stay curious. Find more at spacedew.com and @boggleriley on X