Using observations from the X-ray Imaging and Spectroscopy Mission, astronomers have tracked stellar wind from a forty-solar-mass blue supergiant as it falls onto a neutron star, powering intense X-ray flares in the BP Crucis system located thirteen thousand light-years away.
High-Resolution Spectrometry With Resolve
The space observatory captured detailed spectra of the binary system BP Crucis on Feb. 1, 2025, operating for roughly 16 hours.
These high-resolution readings showed how highly ionized iron atoms lost specific numbers of electrons.
Inside the Blue Supergiant and Pulsar Binary
The primary star, Wray 977, is a blue supergiant roughly sixty times larger than our sun. It continuously expels massive amounts of ionized gas via stellar wind.
Orbiting this behemoth is GX 301-2, a collapsed neutron star measuring just 20 kilometers across despite holding more mass than our sun. This pulsar spins every 11 minutes, sweeping X-ray beams across Earth while completing a 41.5-day orbital journey around Wray 977.
Mapping the Acceleration of Accretion Plasma
Intense X-ray flares erupt for several days near the closest and furthest points of the pulsar’s orbit. Gravitational pull from the neutron star generates dense streams of plasma from the primary star. When the pulsar cuts across this gas stream, it captures stellar material and triggers a flare. Iron absorption lines captured by the Resolve instrument revealed a redshift indicating that gas rushes toward the pulsar at roughly 540,000 kilometers per hour.
Brian Williams, a project scientist at NASA’s Goddard Space Flight Center, noted that the BP Crucis system acts as an ideal laboratory for studying how stellar winds feed energy to pulsars.
When the neutron star enters the thick gas stream, it drags heavy, chaotic accretion material into a spiral before it heats up and releases X-rays. Once the pulsar plunges deeper into the dense flow, lack of angular momentum causes the accretion disk to break apart, sending plasma straight onto the neutron star. XRISM caught the final act of this violent feeding process.
