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

TL;DR

This paper reports the first astronomical detection of a radioactive molecule, $^{26}$AlF, in a stellar remnant, providing new insights into the sources of Galactic $^{26}$Al and stellar evolution.

Contribution

It presents the first direct detection of $^{26}$AlF in space, linking radioactive isotopes to specific stellar remnants and challenging previous assumptions about their origins.

Findings

Detection of $^{26}$AlF toward CK Vul.

Constraints on $^{26}$Al production in stellar mergers.

Implications for the origin of Galactic $^{26}$Al.

Abstract

Decades ago, $\gamma$-ray observatories identified diffuse Galactic emission at 1.809 MeV originating from $\beta^+$ decays of an isotope of aluminium, $^{26}$Al, that has a mean-life time of 1.04 Myr. 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 ($^{26}$AlF). The emission is observed toward CK Vul which is thought to be a remnant of a stellar merger. 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 $^{26}$Al. However, the observation may be a stepping stone for unambiguous identification of other Galactic sources of $^{26}$Al. Moreover, a high content of $^{26}$Al in the remnant indicates that prior to the merger, the CK Vul system contained at least one solar-mass star that evolved to the red giant branch.