From non-ideal magnetohydrodynamics to the structure and evolution of protoplanetary discs

ended

Circumstellar discs are the birthplaces of planets. They form around young protostars and dissipate in a few million years. Modern submillimeter and optical telescopes such as ALMA and VLT/SPHERE are now able to resolve thin structures in the bulk of these objects, such as rings, crescents, spirals and winds, probing the very origin of planetary systems similar to our own. Our current understanding of these discs relies on a very crude modelling of a hypothetic magneto-hydrodynamic (MHD) turbulence thought to play an essential role in the evolution and structure of these systems. However, there is now compelling theoretical and observational evidence that these discs are weakly turbulent, if not laminar, because of their low ionisation fraction and thus poor coupling to the magnetic field. This suggests that subtle MHD processes are driving the dynamics of these objects. Moreover, my recent theoretical breakthroughs demonstrate that these gaseous discs are subject to self-organisation and magneto-thermal winds. These processes play a key role for the disc as they can control its radial structure and evolution. I propose that computing global non-ideal MHD models from massively parallel numerical simulations will shed a new light on these processes, connecting the long-term evolution of these discs to the formation of large scale structures seen by ALMA and SPHERE. We expect MHDiscs to provide reliable global evolution models by coupling gas dynamics to dust and irradiation. These models will be used to predict discriminant observables of the processes I propose, setting the stage for a deeper understanding of the formation of planetary systems.