Simulation of Magnetic Draping

High-resolution X-ray observations have revealed cavities and `cold fronts' with sharp edges in temperature, density, and metallicity within galaxy clusters. Their presence poses a puzzle since these features are not expected to be hydrodynamically stable, or to remain sharp in the presence of diffusion. However, a moving core or bubble in even a very weakly magnetized plasma necessarily sweeps up enough magnetic field to build up a dynamically important sheath around the object; the layer's strength is set by a competition between `plowing up' of field and field lines slipping around the core, and to first order depends only on the ram pressure seen by the moving object.

[ Papers | Movies and Images | Talks ]

“Draping of Cluster Magnetic Fields over Bullets and Bubbles -- Morphology and Dynamic Effects”, Dursi & Pfrommer, ApJ 677:993, 2008. At this link is a PDF version of the paper (8Mb) which contains 3D interactive renderings of several of our simulation results which can be viewed from all angles and zoomed in/out on if you are using a recent version of Adobe Acrobat Reader. A 5Mb version with full-resolution figures but without the 3D interactive renderings is available here. The arXiv version, arXiv:0711.0213, omits the 3D renderings and has lower resolution figures.

“Bubble-Wrap for Bullets: The Stability Imparted by a Thin Magnetic Layer”, Dursi, ApJ 670:221, 207. PDF manuscript available here or at arXiv. In this work, we showed that even a thin draped magnetic field layer can maintain itself and provide some protection against instabilities, at least against those modes in the direction of the magnetic field.

Here is a Quicktime movie of a 3d rendering of the draping process, for the simulation referred to as run F in Dursi & Pfrommer. The movie is also available in avi, mpeg, or windows media.

High resolution still images of the three dimensional renderings of the draping are available for run E, run F, and run G.

A quicktime movie of magnetic draping `bouncing' a massive projectile in 2D is available here. Also available is an avi version and an mpeg version.

Quicktime movies of a thin magnetic layer experiencing a strong shear are available here for the disrupted case where the layer isn't strong enough to supress the instability (Alfvén speed approximately 0.2 times the shear speed) and here for the stabilized case where the Alfvén speed is about 1.25 the shear speed.

Uncovering the cloak of invincibility - The draping of cluster magnetic fields over bullets
Invited colloquium, MPA High Energy Seminar, Oct 12 2007
[PDF]
An invited talk on this work given by Christoph Pfrommer in Oct 2007 at the Max-Planck Instituit für Astrophysik in Garching Germany.

Sweeping up a Magnetic Sheath: Magnetic Draping over Moving Cores and Bubbles in Galaxy Clusters
Accretion and Explosion: the Astrophysics of Degenerate Stars, KITP, May 17 2007
[PDF] [Keynote]
A talk given by Jonathan Dursi while in residence at the KITP program on supernovae in May 2007 during an early stage of this work. Video and audio, as well as the slides, are available at the KITP website.