When the primary star evolves into a giant in a close binary system, it can engulf its companion. The core of the giant star and the companion star then orbit each other in a common stellar envelope and transfer their energy to it. The distance between the two stars shrinks and the envelope is eventually ejected. What remains is a close binary of two stellar cores - the precursor of many fascinating astrophysical phenomena, such as supernovae and the mergers of compact objects that emit gravitational waves. Despite their importance to astrophysics and astronomy, the physical mechanism of this common envelope evolution remains poorly understood, leading to large uncertainties in the modeling of binary stars. Filling this fundamental knowledge gap in the theory of binary star evolution is the goal of the ExCEED project.
Fritz Röpke is a group leader at the Heidelberg Institute for Theoretical Studies (HITS) and Professor at the Department of Physics and Astronomy.