Isotopes of Barium as a Chronometer for Supernova Dust Formation

Abstract

Abstract Ejecta from the explosion of massive stars (core-collapse supernovae) make an important contribution to dust in the interstellar medium. However, dust formation around supernovae is not a simple process, with the formation of several components over time. In particular, the exact timing is a matter of debate. Here, we demonstrate that the isotopic composition of barium in supernova grains that survived in primitive meteorites constitutes a potential chronometer. For a subset of supernova silicon carbide grains (X1 grains), the Ba isotopes indicate that they formed at roughly the same time, and that, at this time, a substantial fraction of the freshly produced unstable 137Cs (half-life 30 yr) had already decayed into 137Ba. Application to the 137Cs/137Ba system of nucleosynthesis models that replicate the abundance patterns of stable neutron capture isotopes in these grains indicates a surprisingly late (∼20 yr) timescale for condensation, a conclusion that naturally rests on the reliability of these models.