NASA's XRISM telescope watched a city-sized dead star swallow gas from a giant neighbor — and clocked it falling at 335,000 mph.
Gas is pouring onto the dead star at about 335,000 mph (540,000 kph). It is the first time anyone has directly watched a stellar wind land on one.
The eater is a neutron star called GX 301-2. It packs more than the Sun's mass into a ball roughly 12 miles wide, and spins once every 11 minutes.
The gas comes from Wray 977, a blue hypergiant about 40 times the Sun's mass and 60 times its size. Stars that big shed material constantly.
A hypergiant's outer layers stream away as a hot wind. Whatever drifts close to the neutron star is caught by its gravity and dragged down.
Neutron stars are what big stars leave behind. The Crab Nebula, seen here, hides one at its heart, born in a supernova people watched in 1054.
Massive stars often come in pairs. This one laps its partner every 41.5 days, and twice an orbit it hits thicker gas and blazes in X-rays.
XRISM watched the pair on Feb. 1, 2025, for about 16 hours, catching the tail end of one of those flares with its Resolve instrument.
Nested foil mirrors funnel X-rays onto the detector. Iron lines in the spectrum shifted red — the fingerprint of gas racing away from us.
The system lies about 13,000 light-years away in Crux, the Southern Cross — far too faint and far too distant to pick out with the naked eye.
Watching wind turn into X-rays shows how the densest objects in the universe grow. The results were published Sept. 18 in Science Advances.