NASA-JAXA XRISM Mission Sees Pulsar Gathering Companion’s ‘Wind’

NASA's XRISM mission has captured unprecedented evidence of a massive star's stellar wind being captured by its neutron star companion and fueling powerful X-ray flares, according to a study published in Science Advances. The researchers examined data from the Japan-led XRISM observatory, which directly observed the process in the BP Crucis system, a high-mass X-ray binary located about 13,000 light-years away in the southern constellation Crux.

BP Crucis consists of a blue hypergiant star, Wray 977, and a neutron star called GX 301-2. The massive star continuously emits a powerful stellar wind, while the neutron star, rotating every 11 minutes, sweeps an X-ray beam toward Earth and classifies as a pulsar. The researchers found that when the pulsar passes through the dense stream of plasma from the stellar wind, strong X-ray flares occur for several days, with the strongest eruptions happening closer to the star where the stream is denser.

The observations, made using XRISM's Resolve instrument on February 1, 2025, revealed highly detailed X-ray spectra with rapid changes in emission and absorption lines. The iron absorption lines observed were displaced to lower energies than in a laboratory, indicating the gas was flowing toward the pulsar at about 335,000 mph (540,000 kph).

This is the first time clear indications of wind plasma falling onto a compact object have been observed, providing a unique opportunity to test understanding of these processes in great detail.