"Ash-fall" induced by molecular outflow in protostar evolution

Abstract

Dust growth and its associated dynamics play key roles in the first phase of planet formation in young stellar objects (YSOs). Observations have detected signs of dust growth in very young protoplanetary disks. Furthermore, signs of planet formation, gaps in the disk at a distance of several 10 astronomical units (AU) from the central protostar are also reported. From a theoretical point of view, however, it is not clear how planet form at the outer region of a disk despite the difficulty due to rapid inward drift of dust so called radial drift barrier. Here, on the basis of three-dimensional magneto-hydrodynamical simulations of disk evolution with the dust growth, we propose a mechanism named "ash-fall" phenomenon induced by powerful molecular outflow driven by magnetic field which may circumvent the radial drift barrier. We found that the large dust which grows to a size of $\sim \cm$ in the inner region of a disk is entrained by an outflow from the disk. Then large dust decoupled from gas is ejected from the outflow due to centrifugal force, enriching the grown dust in the envelope and is eventually fall onto the outer edge of the disk. The overall process is similar to behaviour of ash-fall from volcanic eruptions. In the ash-fall phenomenon, the Stokes number of dust increases by reaccreting to the less dense disk outer edge. This may make the dust grains overcome the radial drift barrier. Consequently, the ash-fall phenomenon can provide a crucial assist for making the formation of the planetesimals in outer region of the disk possible, and hence the formation of wide-orbit planets and the formation of the gaps.

9 pages, 5 figures, accepted for publication in ApJL, typos in Appendix A are fixed

References in corpus (13)

• Closed-form expressions for particle relative velocities induced by turbulence
• Mass Estimates of a Giant Planet in a Protoplanetary Disk from the Gap Structures
• Dust settling in local simulations of turbulent protoplanetary disks
• The Radial Distribution of Dust Particles in the HL Tau Disk from ALMA and VLA Observations
• Signs of Early-Stage Disk Growth Revealed with ALMA
• Grain growth in the envelopes and disks of Class I protostars
• Particle dynamics in discs with turbulence generated by the vertical shear instability
• Low dust emissivities and radial variations in the envelopes of Class 0 protostars: a signature of early grain growth?
• Probing the Protosolar Disk Using Dust Filtering at Gaps in the Early Solar System
• Protostellar collapse: the conditions to form dust rich protoplanetary disks
• Non-linear Development of Secular Gravitational Instability in Protoplanetary Disks
• Early evolution of disk, outflow, and magnetic field of young stellar objects: Impact of dust model
• Conditions for justifying single-fluid approximation for charged and neutral dust fluids and a smoothed particle magnetohydrodynamics method for dust-gas mixture