On March 26, 2026, the Chinese-European Einstein Probe observatory caught an X-ray flash that lasted a little over a quarter of an hour. A thousand seconds. The onboard WXT telescope registered a sharp rise in radiation, then a smooth decline, as if someone had screamed into silence, and the echo slowly faded. Astrophysicists named the event EP260321a.

That scream belonged to a star. Or rather, to its supernova — the explosion that ends the lives of stars tens of times heavier than the Sun. Back in the 1930s, Fritz Zwicky predicted that a supernova's birth begins with a shock breakout: the shock wave from the core collapse punches through the outer layers and bursts into space, like a voice through a barrier. But capturing that moment has been rare — before EP260321a, the only reliable example was supernova SN 2008D.

The reason for EP260321a's long "scream" lay in an unusually dense environment. Modeling showed that the shock wave traveled through a gas envelope — a powerful stellar wind that the star had shed shortly before its death. The mass loss rate reached 1.2×10⁻³ solar masses per year; had it persisted longer, the star would have wasted away in a thousand years. But the wind blew for only a few days: by estimates, the cocoon's total mass was about 10⁻⁵ M☉, gathered within a radius of ~350 solar radii. That dense gas slowed the shock wave and stretched the flash to a thousand seconds.

When the envelope finally breached the outer edge of the cocoon, roughly 1200 seconds after the start, the luminosity dropped sharply. The light curve, calculated from a semi-analytical model, matched the observed points almost perfectly. The emission spectrum, close to Planck's law with a temperature of 1.6 million kelvin, further indicated non-equilibrium processes: the Stefan–Boltzmann law predicts a higher temperature for such luminosity. So the emitting region cools faster than it can reach equilibrium, and that too points to a dense wind.

Thus the X-ray breakthrough told of the star's final days. Its death cry, carried through the gas veil, brought news: shortly before collapse, perhaps due to wave heating during the silicon-burning stage, it expelled a tiny cloud. It is precisely such clouds — nearly invisible yet capable of spawning the brightest flashes — that become sensitive indicators of the final evolution of massive stars. Each new breakthrough brings us closer to deciphering these signals.