KINEMATICS AND DYNAMICS OF SELF-GRAVITATING PROTOSTELLAR DISCS

Protostellar discs are the link between stars and planets: they form with the star, and they are the environments in which planet formation takes place. The ubiquity of substructures in protoplanetary discs shown by ALMA has opened debate as to how the timescales for planet formation align with the established evolutionary sequence for Young Stellar Objects. Under the hypothesis of the planetary interpretation, a robust conclusion is that a substantial part of the planet formation process must overlap with the time when protostellar discs are likely to be young. These findings completely changed our perspective on the timescale for planet formation. Indeed, ALMA observations have indicated that this process must occur within the first million year of the disc's life, a timescale one order of magnitude earlier than previously believed. This shift in perspective poses a challenge to existing planet formation theories, such as the Core Accretion model. At this stage, most of the mass content of the disc has not yet been accreted by the central object. The disc to star mass ratio can be considerably high, making the role of the disc self-gravity of paramount importance. A key consequence of the self-gravity is the development of gravitational instability, that can lead to the formation of grand designed spiral structures, that deeply influence the structure and the dynamics of the disc, and the physical processes happening within. Historically, gravitational instability has been proposed as a pathway for planetary formation, due to the limitations of the core accretion model. However, it lost favour due to the higher likelihood of forming stellar companions rather than planets. Nevertheless, recently, this scenario has gained new interest, when the synergy between gravitational instability and dust dynamics is considered. The work presented in this thesis fits into this line of research. The question we address in this dissertation is: is gravitational instability a viable way to form planets in young protostellar discs?