A runaway Wolf-Rayet star as the origin of 26-Al in the early solar system

Establishing the origin of the short-lived radionuclide (SLR) Al-26, which was present in refractory inclusions in primitive meteorites, has profound implications for the astrophysical context of solar system formation. Recent observations that Al-26 was homogeneously distributed in the inner solar system prove that this SLR has a stellar origin. In this Letter, we address the issue of the incorporation of hot Al-26-rich stellar ejecta into the cold protosolar nebula. We first show that the Al-26 atoms produced by a population of massive stars in an OB association cannot be injected into protostellar cores with enough efficiency. We then show that this SLR likely originated in a Wolf-Rayet star that escaped from its parent cluster and interacted with a neighboring molecular cloud. The explosion of this runaway star as a supernova probably triggered the formation of the solar system. This scenario also accounts for the meteoritic abundance of Ca-41.