When a massive star dies, its core collapses and then explodes as a supernova. The very first light of this explosion, the shock breakout, usually lasts only seconds. But the flash EP260321a stretched out to a thousand seconds. The cause turned out to be a dense gas cloud that the star itself had ejected just days before its death. The Einstein Probe telescope detected it in March 2026, and astrophysicists built a model: the shock wave traveled through this obstacle.
This cloud is the result of a powerful stellar wind: the star was losing mass at a rate that would have completely vaporized it in a thousand years. But the wind blew only briefly, and the cloud's mass was just 10⁻⁵ solar masses — a drop by stellar standards. Yet that drop was enough to slow the wave and stretch the "cry" to a quarter of an hour.
When the wave broke through the cloud, the glow sharply subsided. Thus, the shape of the X-ray curve revealed the star's final days: its death cry through a gaseous veil told how much mass it lost before collapse. Now astrophysicists know that even tiny ejected shells can make breakouts long, and such events are key to the final evolution of massive stars.
If the same mass-loss rate had persisted throughout the progenitor star’s life, it would have shed several solar masses — meaning the enhanced wind blew only briefly, likely due to wave heating during the silicon-burning stage.
The X-ray 'scream' of a dying star recalls the final signal transmission in Stanisław Lem’s novel Solaris, where the ocean sends mysterious bursts carrying information about its structure.