Anisotropic Infall and Substructure Formation in Embedded Disks

Abstract

The filamentary nature of accretion streams found around embedded sources suggests that protostellar disks experience heterogenous infall from the star-forming environment, consistent with the accretion behavior onto star-forming cores in top-down star-cluster formation simulations. This may produce disk substructures in the form of rings, gaps, and spirals that continue to be identified by high-resolution imaging surveys in both embedded Class 0/I and later Class II sources. We present a parameter study of anisotropic infall, informed by the properties of accretion flows onto protostellar cores in numerical simulations, and varying the relative specific angular momentum of incoming flows as well as their flow geometry. Our results show that anisotropic infall perturbs the disk and readily launches the Rossby wave instability. It forms vortices at the inner and outer edges of the infall zone where material is deposited. These vortices drive spiral waves and angular momentum transport, with some models able to drive stresses corresponding to a viscosity parameter on the order of α ∼ 10−2. The resulting azimuthal shear forms robust pressure bumps that act as barriers to radial drift of dust grains, as demonstrated by postprocessing calculations of drift-dominated dust evolution. We discuss how a self-consistent model of anisotropic infall can account for the formation of millimeter rings in the outer disk as well as producing compact dust disks, consistent with observations of embedded sources.

Efficient planet formation by pebble accretion in ALMA rings

“…This leaves the open question of how the first-generation rings form. Due to the great variety in discs properties, it is likely that rings observed in ALMA originate from different mechanisms, e.g., sintering (Okuzumi et al 2016), secular gravitational instability (Tominaga et al 2019), coagulation front of pebbles (Ohashi et al 2021), anisotropic infall (Kuznetsova et al 2022). Such a primordial ring can be the birthplace of the first-generation planet, which can later sculpt the disc to possibly generate new rings.…”

Recent progress with observations and models to characterize the magnetic fields from star-forming cores to protostellar disks

“…The current disk radii estimates from the literature are shown in Figure 4. Such compact disks are difficult to produce in large fractions with purely hydrodynamical analytical models of disk formation conserving angular momentum, but could be a natural outcome of magnetized models of disk formation and models of anisotropic collapse (Hennebelle et al, 2020;Kuznetsova et al, 2022). Obtaining self-consistent disk populations from numerical simulations is quite challenging because it requires being able to treat simultaneously spatial scales sufficiently small to resolve the protostellar disks while in the same time sufficiently advance clump scales allow the formation of a statistically significant number of disks.…”

Direct Formation of Planetary Embryos in Self-gravitating Disks

“…Considering the simulations have an equilibrium gas stability parameter of Q ∼ 1.2-1.4, suggesting that dust particles can become gravitationally unstable and collapse even when the gas disk is marginally stable. If the disk becomes more unstable with time through the accretion of envelope material (Küffmeier et al 2018;Kuznetsova et al 2022), structure in massive/gravitoturbulent disks may be determined not only by the instability of the gas but the dense solid concentrations that form first. On the contrary, due to higher radial dust diffusion, the simulation with the largest dust particles straddles the stability threshold and the particles in the simulation do not collapse into dense clumps.…”