When a massive star reaches the end of its lifecycle, it typically ends in a supernova that shines for several months. A subset of these explosions, however, remains luminous for years, puzzling astronomers.
What drives the extended emission?
New investigations point to a companion star in a close binary as the key factor. In the final stages before core collapse, the primary star ejects a substantial amount of material, creating a dense shell of circumstellar medium around the system.
The ensuing supernova shock wave collides with this shell, producing a sustained interaction that keeps the event bright far longer than a standard explosion. Without such surrounding gas, the energy would dissipate more quickly, and the light curve would decline sharply.
The conclusions stem from observations of several long‑lasting supernovae and from detailed numerical simulations that model the dynamics of the explosion within a pre‑existing envelope. The study suggests that isolated single stars cannot generate this type of prolonged interaction.