Gravitational instability in partially ionized plasmas: A two-fluid approach
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| Format: | Preprint |
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2026
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| author | Misra, A. P. Krishan, V. |
| author_facet | Misra, A. P. Krishan, V. |
| contents | We propose a new two-fluid model for a partially ionized magnetoplasma under gravity, where electrons and neutrals are treated as a single fluid, and 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 is significantly modified by the influence of ion-neutral collisions (with frequency $ν_{\rm{in}}$) 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 $κ\equiv k_x/k_y$ and $f\equivν_{\rm{in}}/Ω_{\rm{ci}}$, where $Ω_{\rm{ci}}$ 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 be maximized for $κ,~f\ll1$, or for $κ>1$ and $f\sim0.64$, and minimized for $f\gg1$ 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_00719 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Gravitational instability in partially ionized plasmas: A two-fluid approach Misra, A. P. Krishan, V. Plasma Physics Solar and Stellar Astrophysics We propose a new two-fluid model for a partially ionized magnetoplasma under gravity, where electrons and neutrals are treated as a single fluid, and 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 is significantly modified by the influence of ion-neutral collisions (with frequency $ν_{\rm{in}}$) 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 $κ\equiv k_x/k_y$ and $f\equivν_{\rm{in}}/Ω_{\rm{ci}}$, where $Ω_{\rm{ci}}$ 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 be maximized for $κ,~f\ll1$, or for $κ>1$ and $f\sim0.64$, and minimized for $f\gg1$ 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. |
| title | Gravitational instability in partially ionized plasmas: A two-fluid approach |
| topic | Plasma Physics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2601.00719 |