Rapid Elimination of Small Dust Grains in Molecular Clouds

Abstract

We argue that impact velocities between dust grains with sizes less than $\sim 0.1$ $\mu m$ in molecular cloud cores are dominated by drift arising from ambipolar diffusion. This effect is due to the size dependence of the dust coupling to the magnetic field and the neutral gas. Assuming perfect sticking in collisions up to $\approx 50$ m/s, we show that this effect causes rapid depletion of small grains - consistent with starlight extinction and IR/microwave emission measurements, both in the core center ($n\sim 10^6$ cm${}^{-3}$) and envelope ($n\sim 10^4$ cm${}^{-3}$). The upper end of the size distribution does not change significantly if only velocities arising from this effect are considered. We consider the impact of an evolved dust size distribution on the gas temperature, and argue that if the depletion of small dust grains occurs as would be expected from our model, then the cosmic ray ionization rate must be well below $10^{-16}$ s${}^{-1}$ at a number density of $10^5$ cm${}^{-3}$.

References in corpus (36)

• The chemical composition of the Sun
• Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC
• Systematic Molecular Differentiation in Starless Cores
• Closed-form expressions for particle relative velocities induced by turbulence
• Probing the evolutionary status of starless cores through N2H+ and N2D+ observations
• Molecular ions in L1544. II. The ionization degree
• The stickiness of micrometer-sized water-ice particles
• Observing the gas temperature drop in the high-density nucleus of L 1544
• Dust coagulation and fragmentation in molecular clouds. I. How collisions between dust aggregates alter the dust size distribution
• A Catalogue of Optically Selected Cores
• The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure
• Electric charging of dust aggregates and its effect on dust coagulation in protoplanetary disks
• Abundant H2D+ in the pre-stellar core L1544
• Direct observation of a sharp transition to coherence in Dense Cores
• The Ubiquity of Micrometer-Sized Dust Grains in the Dense Interstellar Medium
• Cosmic-ray ionisation in circumstellar discs
• Dynamics and Depletion in Thermally Supercritical Starless Cores
• Depletion and low gas temperature in the L183 prestellar core : the N2H+ - N2D+ tool
• The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions
• Protostellar Disk Formation Enabled by Removal of Small Dust Grains
• Modeling Porous Dust Grains with Ballistic Aggregates I: Geometry and Optical Properties
• Decoupling of Magnetic Fields in Collapsing Protostellar Envelopes and Disk Formation and Fragmentation
• Interstellar dust charging in dense molecular clouds: cosmic ray effects
• Consistency of Ambipolar Diffusion Models with Infall in the L1544 Protostellar Core
• Ambipolar-Diffusion Timescale, Star-Formation Timescale, and the Ages of Molecular Clouds: Is There a Discrepancy?
• Cohesion of Amorphous Silica Spheres: Toward a Better Understanding of the Coagulation Growth of Silicate Dust Aggregates
• Efficient Monte Carlo methods for continuum radiative transfer
• Cosmic-ray and X-ray Heating of Interstellar Clouds and Protoplanetary Disks
• Collisions of CO${}_2$ Ice Grains in Planet Formation
• Damping of MHD turbulence in partially ionized plasma: implications for cosmic ray propagation
• Effect of Grain Size on Differential Desorption of Volatile Species and on Non-ideal MHD Diffusivity
• Why does ammonia not freeze out in the center of pre-stellar cores?
• Long-term Simulations of Multi-Dimensional Core-collapse Supernovae: Implications for Neutron Star Kicks
• Gas and dust temperature in pre-stellar cores revisited: New limits on cosmic-ray ionization rate
• Hydrodynamics with gas-grain chemistry and radiative transfer: comparing dynamical and static models
• Driven Multifluid MHD Molecular Cloud Turbulence

Cited by in corpus (22)

• An Ice Age JWST inventory of dense molecular cloud ices
• Protostellar collapse simulations in spherical geometry with dust coagulation and fragmentation
• The cosmic-ray ionisation rate in the pre-stellar core L1544
• Influence of grain growth on CO2 ice spectroscopic profiles : Modelling for dense cores and disks
• The Interplay between Ambipolar Diffusion and Hall Effect on Magnetic Field Decoupling and Protostellar Disc Formation
• The young protostellar disk in IRAS16293-2422 B is hot and shows signatures of gravitational instability
• Effect of grain size distribution and size-dependent grain heating on molecular abundances in starless and pre-stellar cores
• Dust grains cannot grow to millimeter sizes in protostellar envelopes
• Modelling methanol and hydride formation in the JWST Ice Age era
• Evolution of dust porosity through coagulation and shattering in the interstellar medium
• Linking the dust and chemical evolution: Taurus and Perseus -- New collisional rates for HCN, HNC, and their C, N, and H isotopologues
• Implementation of dust particles in three-dimensional magnetohydrodynamics simulation: Dust dynamics in a collapsing cloud core
• Ice mantles on dust grains: dramatic variation of thickness with grain size
• Icy molecule desorption in interstellar grain collisions
• Alignment of dense molecular core morphology and velocity gradients with ambient magnetic fields
• Dust evolution during the protostellar collapse: influence on the coupling between the neutral gas and the magnetic field
• The edge-on disk Tau042021: icy grains at high altitudes and a wind containing astronomical PAHs
• On the propagation of Alfvén waves in the dusty interstellar medium. Can we neglect dust inertia in molecular clouds?
• Birth of magnetized low-mass protostars and circumstellar disks
• A multigrain-multilayer astrochemical model with variable desorption energy for surface species
• On the 3D time evolution of the dust size distribution in protostellar envelopes
• Thermal damping of Weak Magnetosonic Turbulence in the Interstellar Medium