Binary evolution and angular momentum transport during common envelope post-dynamical spiral-in phase¶

Common envelope evolution is arguably the most crucial major process in binary star evolution, but also the least-well-constrained and more generally one of the most important unsolved challenge in stellar evolution. Despite being numerically challenging and subject to major uncertainties, 3D–hydrodynamic simulations have provided a comprehensive understanding of the dynamical in-spiral of the secondary star. However, because of the wide range of temporal and spatial scales that need to be resolved and the associated high numerical cost, such simulations are often halted soon after the end of the dynamical in-spiral phase. One thus has to revert to 1D models to simulate the entire common envelope evolution, and suffer their associated limitations. I will present results from the first 3D–hydrodynamic simulations focusing on the post-dynamical phase by means of an original setup mimicking the preceding rapid in-spiral, making use of the Athena++ code to solve the hydrodynamics equations in spherical coordinates. We show that the balance between accretion and gravitational torque suggests a contraction of the orbit on a time-scale of the order O(10^3) orbital periods, that is much shorter than the expected thermal time-scale. We discuss the short-term variability of mass and angular momentum accretion and its remarkable similarity with that in circumbinary disks. Finally, we discuss angular momentum transport within the shared envelope, and the relative importance of turbulence contribution