Positive Feedback II: How Dust Coagulation inside Vortices Can Form Planetesimals at Low Metallicity

Abstract

The origin of planetesimals ($\sim$100 km planet building blocks) has confounded astronomers for decades, as numerous growth barriers appear to impede their formation. In a recent paper we proposed a novel interaction where the streaming instability (SI) and dust coagulation work in tandem, with each one changing the environment in a way that benefits the other. This mechanism proved effective at forming planetesimals in the fragmentation-limited inner disk, but much less effective in the drift-limited outer disk, concluding that dust traps may be key to forming planets at wide orbital separations. Here we explore a different hypothesis: That vortices host a feedback loop in which a vortex traps dust, boosting dust coagulation, which in turn boosts vortex trapping. We combine an analytic model of vortex trapping with an analytic model of fragmentation limited grain growth that accounts for how dust concentration dampens gas turbulence. We find a powerful synergy between vortex trapping and dust growth. For $\alpha \le 10^{-3}$ and solar-like metallicity this feedback loop consistently takes the grain size and dust density into the planetesimal formation region of the streaming instability (SI). Only in the regime of strong turbulence ($\alpha \ge 3\times 10^{-3}$) does the system often converge to a steady state below the SI criterion. The combination of vortex trapping with dust coagulation is an even more powerful mechanism than the one involving the SI. It is effective at lower metallicity and across the whole disk -- anywhere that vortices form.

4 pages, 2 figures, submitted to A&A Letters

References in corpus (24)

• Rapid planetesimal formation in turbulent circumstellar discs
• Streaming Instabilities in Protoplanetary Disks
• A simple model for the evolution of the dust population in protoplanetary disks
• Particle Stirring in Turbulent Gas Disks: Including Orbital Oscillations
• The outcome of protoplanetary dust growth: pebbles, boulders, or planetesimals? II. Introducing the bouncing barrier
• The outcome of protoplanetary dust growth: pebbles, boulders, or planetesimals? I. Mapping the zoo of laboratory collision experiments
• Closed-form expressions for particle relative velocities induced by turbulence
• Forming Planetesimals in Solar and Extrasolar Nebulae
• Particle Clumping and Planetesimal Formation Depend Strongly on Metallicity
• How to form planetesimals from mm-sized chondrules and chondrule aggregates
• The subcritical baroclinic instability in local accretion disc models
• Steady state of dust distributions in disk vortices: Observational predictions and applications to transitional disks
• Dusty gas with one fluid
• Embryos grown in the dead zone: Assembling the first protoplanetary cores in low mass self-gravitating circumstellar disks of gas and solids
• Particle Trapping and Streaming Instability in Vortices
• The baroclinic instability in the context of layered accretion. Self-sustained vortices and their magnetic stability in local compressible unstratified models of protoplanetary disks
• A thermodynamic view of dusty protoplanetary disks
• How dust fragmentation may be beneficial to planetary growth by pebble accretion
• From Dust to Planetesimals: Criteria for Gravitational Instability of Small Particles in Gas
• On the Stability of Dust-Laden Protoplanetary Vortices
• Dusty disc-planet interaction with dust-free simulations
• Morphological signatures induced by dust back reaction in discs with an embedded planet
• Observation of bottom-up formation for charged grain aggregates related to pre-planetary evolution beyond the bouncing barrier
• Positive Feedback: How a Synergy Between the Streaming Instability and Dust Coagulation Forms Planetesimals

Cited by in corpus (1)

• Gas dynamics around dust asymmetries in turbulent disks