Astronomers using the XRISM space telescope have discovered something unexpected: powerful winds blowing from the neutron star system GX13+1 are much slower and denser than those from supermassive black holes.

GX13+1 is the collapsed core of a dead star, surrounded by a hot accretion disk. As matter spirals in, it releases X-rays — and creates winds that shape the surrounding space. Normally, at the so-called Eddington limit, these winds should blast outward at a fraction of light speed.

But XRISM’s ultra-precise Resolve instrument caught GX13+1 during a sudden flare — and the winds clocked in at just 1 million km/h. Sounds fast, but compared to black hole winds, which reach 200 million km/h, it’s sluggish.

Even more surprising, the neutron star’s wind was thick and smooth, unlike the ultrafast, clumpy winds from black holes.

Why the difference? Researchers think it’s due to disk temperature. Supermassive black holes have cooler, UV-emitting disks that push matter more efficiently, while neutron stars and small black holes produce hotter X-ray disks, less effective at driving winds.

This finding reshapes how we understand cosmic winds — the very forces that can spark star formation, halt it, or even regulate galaxy growth.

XRISM has just begun its mission, but it’s already rewriting the rules of extreme astrophysics.