The Non-Linear Growth of the Magnetic Rayleigh-Taylor Instability

TL;DR

This study investigates how magnetic field strength affects the non-linear development of the Rayleigh-Taylor Instability in astrophysical plasmas, revealing that stronger fields reduce bubble growth but enhance spike growth, creating asymmetry.

Contribution

It provides the first detailed numerical analysis of the non-linear magnetic RTI considering realistic astrophysical magnetic field ratios and reveals complex asymmetrical effects.

Findings

Stronger magnetic fields reduce bubble growth in RTI.

Increased magnetic fields enhance spike growth, creating asymmetry.

Greater asymmetry correlates with less efficient gravitational energy release.

Abstract

This work examines the effect of the embedded magnetic field strength on the non-linear development of the magnetic Rayleigh-Taylor Instability (RTI) (with a field-aligned interface) in an ideal gas close to the incompressible limit in three dimensions. Numerical experiments are conducted in a domain sufficiently large so as to allow the predicted critical modes to develop in a physically realistic manner. The ratio between gravity, which drives the instability in this case (as well as in several of the corresponding observations), and magnetic field strength is taken up to a ratio which accurately reflects that of observed astrophysical plasma, in order to allow comparison between the results of the simulations and the observational data which served as inspiration for this work. This study finds reduced non-linear growth of the rising bubbles of the RTI for stronger magnetic fields, and that this is directly due to the change in magnetic field strength, rather than the indirect effect of altering characteristic length scales with respect to domain size. By examining the growth of the falling spikes, the growth rate appears to be enhanced for the strongest magnetic field strengths, suggesting that rather than affecting the development of the system as a whole, increased magnetic field strengths in fact introduce an asymmetry to the system. Further investigation of this effect also revealed that the greater this asymmetry, the less efficiently the gravitational energy is released. By better understanding the under-studied regime of such a major phenomenon in astrophysics, deeper explanations for observations may be sought, and this work illustrates that the strength of magnetic fields in astrophysical plasmas influences observed RTI in subtle and complex ways.