The impact of astrophysical dust grains on the confinement of cosmic rays

Abstract

We argue that charged dust grains could significantly impact the confinement and transport of galactic cosmic rays. For sub-GeV to ~1000GeV cosmic rays, small-scale parallel Alfvén waves, which isotropize cosmic rays through gyro-resonant interactions, are also gyro-resonant with charged grains. If the dust is nearly stationary, as in the bulk of the interstellar medium, Alfvén waves are damped by dust. This will reduce the amplitude of Alfvén waves produced by the cosmic rays through the streaming instability, thus enhancing cosmic-ray transport. In well-ionized regions, the dust damping rate is larger by a factor of ~10 than other mechanisms that damp parallel Alfvén waves at the scales relevant for ~GeV cosmic rays, suggesting that dust could play a key role in regulating cosmic-ray transport. In astrophysical situations in which the dust moves through the gas with super-Alfvénic velocities, Alfvén waves are rendered unstable, which could directly scatter cosmic rays. This interaction has the potential to create a strong feedback mechanism where dust, driven through the gas by radiation pressure, then strongly enhances the confinement of cosmic rays, increasing their capacity to drive outflows. This mechanism may act in the circumgalactic medium around star-forming galaxies and active galactic nuclei.

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Cited by in corpus (5)

• Towards First-principle Characterization of Cosmic-ray Transport Coefficients from Multi-scale Kinetic Simulations
• Stress-Testing Cosmic Ray Physics: The Impact of Cosmic Rays on the Surviving Disk of Ram Pressure Stripped Galaxies
• Cosmic-ray current-driven instabilities -- revisiting environmental conditions
• Numerical Study of Cosmic Ray Confinement through Dust Resonant Drag Instabilities
• Effect of cosmic rays and ionizing radiation on observational ultraviolet plasma diagnostics in the circumgalactic medium