Strong suppression of heat conduction in a laboratory replica of galaxy-cluster turbulent plasmas

TL;DR

This study demonstrates that in a laboratory plasma replica of galaxy-cluster conditions, heat conduction is strongly suppressed, leading to significant temperature variations similar to those observed in actual galaxy clusters.

Contribution

The paper presents the first laboratory experiment replicating galaxy-cluster plasma conditions, showing that magnetic turbulence can suppress heat conduction by over two orders of magnitude.

Findings

Heat conduction is suppressed by more than 100 times in the experiment.

Significant small-scale temperature variations are observed.

Results support the idea that magnetic turbulence limits heat transfer in galaxy clusters.

Abstract

Galaxy clusters are filled with hot, diffuse X-ray emitting plasma, with a stochastically tangled magnetic field whose energy is close to equipartition with the energy of the turbulent motions \cite{zweibel1997, Vacca}. In the cluster cores, the temperatures remain anomalously high compared to what might be expected considering that the radiative cooling time is short relative to the Hubble time \cite{cowie1977,fabian1994}. While feedback from the central active galactic nuclei (AGN) \cite{fabian2012,birzan2012,churazov2000} is believed to provide most of the heating, there has been a long debate as to whether conduction of heat from the bulk to the core can help the core to reach the observed temperatures \cite{narayan2001,ruszkowski2002,kunz2011}, given the presence of tangled magnetic fields. Interestingly, evidence of very sharp temperature gradients in structures like cold fronts implies a high degree of suppression of thermal conduction \cite{markevitch2007}. To address the problem of thermal conduction in a magnetized and turbulent plasma, we have created a replica of such a system in a laser laboratory experiment. Our data show a reduction of local heat transport by two orders of magnitude or more, leading to strong temperature variations on small spatial scales, as is seen in cluster plasmas \cite{markevitch2003}.