Joint Astrophysical Colloquium
The Turbulent Support (TS) and Global Hierarchical Collapse (GHC) models for molecular clouds compared. Differences, convergence, and myths.
Enrique Vázquez-Semadeni (Instituto de Radioastronomía y Astrofísica (IRyA), UNAM)
Thursday 11/09/2025 @ 11:30, Sala Antonio Sollima (IV piano Battiferro)
I will present a detailed comparison between the "turbulent support" (TS) and "global hierarchical collapse" (GHC) theoretical models for molecular clouds and star formation, as frameworks for the interpretation of observations and simulations. After a brief recap of the origins of both models, I will discuss their fundamental premises and interpretation of molecular cloud properties, scaling relations, energy balance, and star formation activity. The fundamental distinction is that TS assumes that giant molecular clouds (GMCs), on scales 10-100 pc are supported against collapse by turbulent motions, and interprets the widths of molecular lines exclusively as turbulence that opposes gravity. Instead, GHC incorporates a description of GMC-scale infall motions and accretion at all scales onto and inside the clouds, making specific predictions for the evolution of the clouds and their substructures, which increase their masses, sizes, and star formation rates (SFRs). Also, it explicitly considers that the total velocity dispersion and the kinetic energy Ek include compressive motions (of either gravitational or inertial origin) that do not oppose gravity, but rather work together with it. In consequence, values of the virial parameter (av = 2 Ek/Eg) up to ~3 can be considered as indicative of significant gravitational binding. In relation to the SFR, in TS it is determined by parameters of the turbulence, which is considered as an external agent, and therefore the SFR is not subject to secular evolution. Under GHC, instead, the main parameter regulating the evolution of the SFR is the accretion rate onto the cloud and the gravitational contraction, causing the SFR to first increase over time, until feedback begins to reduce it, by destruction of the local collapse flow. Finally, under TS, hub-filament systems (HFSs) are a consequence of turbulent compressions, while under GHC they are the result of anisotropic gravitational contraction from the cloud scale. A few strat