XRISM recorded plasma falling towards the X-ray pulsar GX 301\u22122 at least 540,000 kilometres per hour while the neutron star passed through a dense stream in the wind of the blue hypergiant Wray 977.<\/p>\n
The Japan-led observatory began observing BP Crucis on 1 February 2025, collecting about 16 hours of usable data near the end of a strong flare. Resolve measured the gas\u2019s motion and spectral changes that constrain its changing arrangement around the pulsar.<\/p>\n
This is one observation of one flare. The direct result is spectroscopic evidence for inflow. Disk breakup and reversal are interpretations drawn from XRISM spectra, long-term Fermi timing and flow modelling, not frames from a resolved image.<\/p>\n
Iron lines measured gas falling in<\/p>\n
Roi Rahin and 12 colleagues report in Science Advances<\/a> that Resolve detected redshifted lines from highly ionised iron and transitions from less ionised states.<\/p>\n The absorption lines appeared at lower energies than the same atomic transitions measured in a laboratory. That redshift shows that the plasma was moving away from Earth. Establishing motion towards GX 301\u22122 requires the orbital corrections and physical consistency checks that follow.<\/p>\n The two strongest lines were redshifted by 419 and 443 kilometres per second in the observer\u2019s frame, with statistical uncertainties near 25 kilometres per second. Correcting for Earth, BP Crucis and the neutron star\u2019s uncertain orbital velocity gives inflow faster than 150 kilometres per second under all three ephemerides tested.<\/p>\n Under the team\u2019s adopted ephemeris, the range is 150 to 180 kilometres per second. The widely quoted 540,000 kilometres per hour is therefore a lower bound, not an exact speed.<\/p>\n The lines changed from absorption, through mixed intervals, to emission. Absorption marks gas in front of the bright X-ray source; emission can arrive from a wider volume. The transition gave evidence that the flow geometry was rearranging while matter accreted.<\/p>\n \u201cDirect\u201d needs a precise meaning here. XRISM did not photograph a stream touching the neutron star. It measured the motion and changing location of the plasma through its effect on X-ray photons.<\/p>\n A hypergiant feeding a city-sized remnant<\/p>\n BP Crucis lies about 13,000 light-years away in Crux. Wray 977 has roughly 40 solar masses and 60 solar radii. Its companion packs more than a solar mass into a neutron star about 20 kilometres across. GX 301\u22122 rotates every 11 minutes and orbits in 41.5 days.<\/p>\n \t\t\t\t\t\tWhat changed in the universe since you were born?<\/p>\n Six sourced measurements. No predictions. No astrology.<\/p>\n Wray 977 constantly loses ionised gas. Several-day X-ray flares occur near the pulsar\u2019s closest and farthest orbital points. Astronomers think GX 301\u22122\u2019s gravity helps create a denser stream within the wind; the pulsar brightens when it crosses and captures some of that material. The passage lasts about four days.<\/p>\n XRISM has already used Resolve to disentangle fast, Doppler-shifted gas in the stellar wind around Cygnus X-3<\/a>, another compact object embedded in a massive companion\u2019s outflow. The BP Crucis observation adds a time sequence close to a neutron star while a flare is under way.<\/p>\n Where the broken, reversed disk enters the story<\/p>\n The detailed disk sequence comes from the researchers\u2019 interpretation, set out in NASA\u2019s account<\/a>. On entry, captured gas may have enough sideways motion to form a turbulent disk and spiral inward.<\/p>\n Farther in, the pulsar moves more directly against the flow. Incoming material then lacks the angular momentum to sustain a disk. The structure breaks apart and plasma falls more radially. XRISM observed near the end of this proposed phase.<\/p>\n Near the far edge of the stream, the relative flow changes once more. A messy disk can briefly re-form, now rotating in the opposite direction, before disappearing as the pulsar exits.<\/p>\n XRISM caught only the end of the stronger pre-periastron flare. It did not observe the initial disk, its breakup and the later reversed disk from start to finish. The peer-reviewed paper phrases the measured geometry more cautiously as an evolution from predominantly radial inflow to a transverse, potentially disk-like configuration. The spectrum does not independently resolve a disk or measure its rotation on the sky.<\/p>\n A different kind of disk-reversal evidence<\/p>\n