On the support of neutrals against gravity in solar prominences

TL;DR

This study demonstrates through two-dimensional simulations that neutrals in solar prominences are supported against gravity via strong coupling with ions, with charge exchange playing a significant role in maintaining neutral support.

Contribution

It introduces a multi-fluid model considering collisions and charge exchange, showing neutrals can be dynamically suspended in prominences, a novel insight into prominence support mechanisms.

Findings

Neutrals exhibit very small downflow velocities due to strong coupling.

Charge exchange interactions are about three times more effective than elastic collisions.

The prominence plasma behaves like a single fluid with combined density.

Abstract

Cool and dense prominences found in the solar atmosphere are known to be partially ionized because of their relative low temperature. In this Letter, we address the long-standing problem of how the neutral component of the plasma in prominences is supported against gravity. Using the multiple fluid approach we solve the time-dependent equations in two dimensions considering the frictional coupling between the neutral and ionized components of the magnetized plasma representative of a solar prominence embedded in a hot coronal environment. We demonstrate that given an initial density enhancement in the two fluids, representing the body of the prominence, the system is able to relax in the vicinity of magnetic dips to a stationary state in which both neutrals and ionized species are dynamically suspended above the photosphere. Two different coupling processes are considered in this study, collisions between ions and neutrals and charge exchange interactions. We find that for realistic conditions ions are essentially static while neutrals have a very small downflow velocity. The coupling between ions and neutrals is so strong at the prominence body that the behavior is similar to that of a single fluid with an effective density equal to the sum of the ion and neutral species. We also find that the charge exchange mechanism is about three times more efficient sustaining neutrals than elastic scattering of ions with neutrals.