Gravitational instability in partially ionized plasmas: A two-fluid approach

2026/01/02 by A. P. Misra, V. Krishan
Physics and Astronomy · #physics.plasm-ph #astro-ph.SR

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Abstract

We propose a new two-fluid model for a partially ionized magnetoplasma under gravity, in which electrons and neutrals are treated as a single fluid, while singly charged positive ions are a separate fluid. We observe that the classical result of gravitational instability (also known as Rayleigh-Taylor instability) in fully ionized plasmas becomes significantly modified by the influence of ion-neutral collisions (with frequency ν_\rmin) and transverse wave numbers (k_x and k_y). The instability growth rate can be enhanced or decreased depending on the values of the ratios κ≡ k_x/k_y and f≡ν_\rmin/Ω_\rmci, where Ω_\rmci is the ion-cyclotron frequency. We also estimate the growth rates relevant to the ionospheric E-region and solar atmosphere, noting that such growth rates can have a maximum for κ,~f≪1, or for κ>1 and f∼0.64, and minimized for f≫1 irrespective of the value of κ. Furthermore, the timescale of instability ranges from 1 minute to 2 minutes in the solar atmosphere, while in the E region, it ranges from 1 minute to 80 minutes. The latter can be a satisfactory result for the reported lifetime of solar prominence threads.

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