Rethinking about gravitational instability as a planet formation scenario
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. Thanks to ALMA radio telescope, we are collecting plenty of data about these systems, showing a high degree of complexity in their structure, morphology and kinematics. Many discs exhibit substructures that are consistent with - and often interpreted as - the theoretically expected signature of planet-disc interaction. 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 young, likely to be self-gravitating and, possibly, gravitationally unstable. Hence, a natural question to ask is: what is the role of the disc self-gravity in the context of plant formation?
In this seminar, I investigate both gas kinematics and dust dynamics of young protostellar discs. As for the gas kinematics, gravitational instability leaves clear observational signatures, known as “GI wiggles”. Through their characterisation, it is possible to investigate protoplanetary disc mass and cooling. These information shed light on fundamental questions like the amount of mass available for planet formation, and the transport of angular momentum. As for the dust dynamics, it is well known that the spiral perturbations induced by gravitational instability can trap dust very efficiently, possibly making the dust unstable itself. This mechanism could, in principle, solve the conundrum of planetesimal formation, forming planetary cores during the early stages of protostellar disc life. In this context, I present a new analytical framework to characterise the interplay between gravitational instability and the aerodynamical coupling between gas and dust, fundamental to understand planet formation. To conclude, I test this model through numerical simulations, showing that dust collapse inside gas spiral arms is a viable way to form planetary cores in young protostellar systems.