Gravitational instability of thick gas discs: from protoplanetary to galactic scales
Carlo Nipoti (Unibo-DIFA)
Tuesday 07/02/2023 @ 14:00, Sala IV piano Battiferro - Presenza + remoto
Fragmentation of rotating gas systems via gravitational instability is a crucial mechanism in several astrophysical processes, such as formation of planets in protoplanetary discs and of star clusters in galactic discs. Gravitational instability is fairly well understood for infinitesimally thin discs, but the thin-disc approximation is often not justified. I will present new 3D instability criteria, which can be used to determine whether and where a rotating system of given 3D structure is prone to clump formation. For a vertically stratified gas disc of thickness h_z, the instability criterion takes the form Q_3D<1, where Q_3D, depending on h_z and on the local gas properties, is a 3D analogue of the classical 2D Toomre's Q parameter. I will show that, in unstable discs, the conditions for instability are typically met close to the mid-plane, where the perturbations that are expected to grow have characteristic radial extent of a few h_z.