Three-dimensional Magnetohydrodynamic Simulations of Buoyant Bubbles in Galaxy Clusters

TL;DR

This study uses 3D magnetohydrodynamic simulations to investigate how buoyant bubbles in galaxy clusters evolve, highlighting the influence of magnetic fields on their stability, shape, and dynamics.

Contribution

It extends previous 2D simulations to 3D, demonstrating the effects of magnetic field strength and configuration on bubble evolution in galaxy clusters.

Findings

Bubbles evolve into toroidal shapes, forming vortex rings.

Magnetic fields with beta ~ 10^2 can bifurcate bubbles before they rise a scale height.

Tangling magnetic fields inside bubbles have minimal impact on evolution.

Abstract

We report results of 3D MHD simulations of the dynamics of buoyant bubbles in magnetized galaxy cluster media. The simulations are three dimensional extensions of two dimensional calculations reported by Jones & De Young (2005). Initially spherical bubbles and briefly inflated spherical bubbles all with radii a few times smaller than the intracluster medium (ICM) scale height were followed as they rose through several ICM scale heights. Such bubbles quickly evolve into a toroidal form that, in the absence of magnetic influences, is stable against fragmentation in our simulations. This ring formation results from (commonly used) initial conditions that cause ICM material below the bubbles to drive upwards through the bubble, creating a vortex ring; that is, hydrostatic bubbles develop into "smoke rings", if they are initially not very much smaller or very much larger than the ICM scale height. Even modest ICM magnetic fields with beta = P_gas/P_mag ~ 10^3 can influence the dynamics of the bubbles, provided the fields are not tangled on scales comparable to or smaller than the size of the bubbles. Quasi-uniform, horizontal fields with initial beta ~ 10^2 bifurcated our bubbles before they rose more than about a scale height of the ICM, and substantially weaker fields produced clear distortions. On the other hand, tangled magnetic fields with similar, modest strengths are generally less easily amplified by the bubble motions and are thus less influential in bubble evolution. Inclusion of a comparably strong, tangled magnetic field inside the initial bubbles had little effect on our bubble evolution, since those fields were quickly diminished through expansion of the bubble and reconnection of the initial field.