Explaining Common Envelope Evolution and Dynamics in binary stellar systems

A thorough understanding of stellar evolution is key to nearly any branch of astrophysics. The majority of stars evolves in binary or multiple systems and interactions often occur between their components. Such dynamical interaction phases are pivotal for the fate of the system and its constituents, but they elude classical stellar modeling. Common-envelope phases, in which a compact companion spirals into the envelope of a giant primary star, are the glaring gaps in our knowledge and pose one of the last unsolved fundamental problems to stellar astrophysics.The ExCEED project breaks new ground by developing a strategy to reach a comprehensive understanding of common-envelope evolution. It combines leading three-dimensional magnetohydrodynamic moving-mesh simulations with innovative models of physical processes to decipher the dynamical interaction between the stellar cores and the envelope material. On this basis, the post-common envelope evolution is explored by consistently linking to classical one-dimensional models. Predictions for astronomical observables are derived and a faithful effective prescription for representing common-envelope phases in binary stellar evolution and population synthesis calculations is constructed.The new understanding of common-envelope evolution provided by the ExCEED project marks a break- through in stellar astrophysics and has implications beyond this field. ExCEED finally settles the long- standing questions of the mechanism of envelope ejection and the orbital separation of the post-common envelope remnant binary system. This allows to understand the formation of the targets of gravitational- wave astronomy that holds promise to solve problems of fundamental physics, the progenitors of Type Ia supernovae, and many other astrophysical events.