Astronomers using ALMA and NOEMA have made the first definitive detection of a radioactive molecule in interstellar space. The radioactive part of the molecule is an isotope of aluminium. The observations reveal that the isotope was dispersed into space after the collision of two stars, that left behind a remnant known as CK Vulpeculae. This is the first time that a direct observation has been made of this element from a known source. Previous identifications of this isotope have come from the detection of gamma rays, but their precise origin had been unknown.