The Production of 26Al in Supermassive Stars and the Gamma-Ray Line Flux from the Galactic Center

The evolution through contraction and explosion of a high-metallicity (Z = 0.04) supermassive star of 500,000 solar masses is computed. It is shown that in the inner 20-percent of the star, a significant fraction of the preexisting magnesium is converted into Al-26 leading to the production of about 50 solar masses of Al-26. This amount is sufficient to explain the observed 1.8 MeV gamma-ray line flux from the Galactic center if such a supermassive star exploded there within the last two million years. The ejecta will be enriched in the isotopes C-13 and O-17, but, with the exception of lithium and nitrogen, all elements are produced in roughly solar relative proportions.