THE IMPACT OF TRIPLE STELLAR SYSTEMS ON PROTOSTELLAR DISC DYNAMICS

Theoretical challenges in modelling multiple stellar systems are mirrored by observational limitations, with multiplicity often concealed within disc cavities and hidden by surrounding material. Nevertheless, advancements in observational instruments are steadily revealing multiple stellar systems within discs, while astrometry is becoming more sensitive. The present capabilities offer us the opportunity to develop a comprehensive theory for disc and planet formation in multiple stellar systems and prepare our models for forthcoming observational data. Throughout this thesis, I underlined the significance of taking into account multiple stellar systems in models of stellar and planetary formation. Ignoring the influence of multiplicity restricts the range of configurations for which our theories hold. Despite the added complexity, multiple stellar systems provide a unique way for a more profound understanding of the overall stellar and planet formation processes. The broader parameter space and diverse mechanisms inherent to these systems yield an abundance of observables that probe various aspects of ongoing physical processes, from gas hydrodynamics to dust dynamics and evolution. Importantly, these observables are indicative of fundamental hydrodynamical properties governing stellar and planet formation across diverse systems, not just those with two or more stars. In particular, this thesis challenges the oversimplification of reducing the dynamics of multiple stellar systems with more than two stars to two-body system dynamics. It asserts the critical importance of accounting for the secular evolution of these systems and highlights additional phenomena inherent to multiple stellar systems that can elucidate observations, providing otherwise inaccessible insights in stellar formation physics.