Astronomers have recorded explosions that smash two forming massive stars together in tight interstellar cradles. The energy of such a blast is comparable to a full-fledged exploding dying star and can briefly outshine an entire galaxy.

The matter expands in a miniature Big Bang: the farther the gas from the center, the faster it flies away. This motion, revealed by the color shift of light, mirrors the galaxy recession discovered by Edwin Hubble and Georges Lemaître. The collision solves a growth paradox: a young star's radiation should blow away infalling matter, but a forceful merger helps bypass the limit. The culprits themselves often get flung from the epicenter, leaving behind a void. Computer models, accounting for gas surroundings, magnetic field interplay, and streams of energetic particles, back up this picture. Radio telescopes and spectral analysis have for the first time allowed us to reconstruct it.