In the binary system 4U 1624-49, a neutron star pulls gas from its companion star. This gas spirals into a glowing disk, like water in a funnel. And from the edge of this funnel, a hot stream tears away — hydrogen and other elements fly off at speeds up to 320 kilometers per second.
The X-ray telescope XRISM watched the system for a full orbit—21 hours. The Resolve spectrometer revealed narrow absorption lines: gas between us and the star absorbs light at specific frequencies. From the shift of these lines, astronomers calculated the wind speed — from 200 to 320 kilometers per second. The closer to the moment when the disk is edge-on and briefly hides the star, the broader the lines. This means the wind becomes more turbulent, like water around a rock.
The wind is launched from the outer edge of the disk, not from the inside, and it does not split into separate jets. This behavior is explained by radiation pressure: photons push the gas outward. It is like a solar sail, but instead of a sail, there is a plasma cloud, and instead of the Sun, a hot disk around a neutron star.
The wind speed in this system is hundreds of times the speed of sound in air, such a flow would travel from Earth to the Moon in 20 minutes.