Astronomical detection of radioactive molecule 26AlF in the remnant of an ancient explosion

Decades ago, gamma-ray observatories identified diffuse Galactic emission at 1.809 MeV1-3 originating from beta(+) decays of an isotope of aluminium, Al-26, that has a mean lifetime of 1.04 million years(4). Objects responsible for the production of this radioactive isotope have never been directly identified owing to insufficient angular resolutions and sensitivities of the gamma-ray observatories. Here, we report observations of millimetre-wave rotational lines of the isotopologue of aluminium monofluoride that contains the radioactive isotope ((AlF)-Al-26). The emission is observed towards CK Vul, which is thought to be a remnant of a stellar mergers(5-)(7). Our constraints on the production of( 26)Al, combined with the estimates on the merger rate, make it unlikely that objects similar to CK Vul are major producers of Galactic Al-26. However, the observation may be a stepping stone for unambiguous identification of other Galactic sources of Al-26. Moreover, a high content of Al-26 in the remnant indicates that, before the merger, the CK Vul system contained at least one solar-mass star that evolved to the red giant branch.