Physical Society Colloquium

Turbulent nuclear burning and the exotic formation of heavy elements in stars

Falk Herwig

Department of Physics and Astronomy
University of Victoria

Many aspects of how elements form and how they are mixed through convection in stars, and how these two processes interact is still poorly understood. One example is when proton-rich envelope material is ingested into the C12-rich, convective He-burning shell through turbulent entrainment. New large-scale 3-D simulations of this entrainment process at convective boundaries and the subsequent advection and nuclear reaction of protons with C12 show that the traditional spherically-symmetric modeling approach (stellar evolution) is inapprorpiate here. The coupling of turbulent convective flow and rapid nuclear energy release leads to a previously unknown global oscillation of shell H-ingestion. This is the site of the i process, an intermediate neutron-capture process that can be observed in a nearby pre-white dwarf/post-AGB star (Sakurai's object), in pre-solar meteoritic grains and - we claim - in the abundance patterns of very metal-poor stars. The investigation of the exotic properties of the i process requires presently unknown nuclear physics data of unstable isotopes.