Circumbinary disc evolution in multiple stellar systems

Young stars predominantly form within multiple stellar systems. In these multi-star systems, a significant fraction of close binaries are surrounded by circumbinary disks. In such dynamic and highly perturbed environments, planet formation differs substantially from the classical scenario of discs around single stars. The presence of two central stars induces complex structures in the disc, such as inner cavities, spiral arms, and density asymmetries. Moreover, perturbations from external stellar companions affect the structure and relative inclination of the discs. This profoundly modifies the dynamics of gas and dust within these discs, and therefore the process of planet formation.

The objective of this thesis is to study in detail the dynamics and evolution of circumbinary discs in multiple stellar systems. Particular attention will be given to alignment mechanisms and angular momentum transport, as well as to the evolution of dust in these perturbed environments. The central question is to understand how the orbital configuration of a multiple stellar system modifies the planet formation process and to determine the planetary architectures expected in such systems.

Initially, the dynamics of circumbinary discs will be modeled using the 3D hydrodynamical code Phantom. These simulations will allow us to characterise the evolution of disk structures under the influence of the gravitational interactions of all the stars. The results will be coupled with the radiative transfer code MCFOST in order to produce synthetic multi-wavelength observations. This approach will allow a direct link between the simulated physical properties of the disc and the resulting observables. In parallel, high angular resolution observations of circumbinary disks will be analysed, in particular using the millimeter interferometer ALMA. These data will constrain the spatial distribution of dust, identify substructures (rings, cavities, asymmetries), and estimate grain sizes. The comparison between simulations and observations will provide a robust framework for testing the proposed models.
This project thus aims to provide a comprehensive and coherent understanding of planet formation in circumbinary disks by combining advanced numerical simulations and state-of-the-art observations. It will contribute to shedding light on the diversity of observed planetary architectures and to better constraining the conditions required for planet formation in multiple systems.