Tuesday

Clusters of galaxies are filled with weakly-collisional, high-beta plasma. Such plasma is prone to kinetic gyroscale instabilities. These instabilities induce microfluctuations of the electromagnetic field that scatter off particles, effectively increasing their collision rate and suppressing viscosity in the bulk intergalactic gas. Using deep Chandra observations of the Coma cluster, we measure a power spectrum of fluctuations down to spatial scales comparable to the Coulomb mean free path. We find that the slope of the spectrum is significantly shallower than the expected one in a Coulomb-collision-dominated plasma. This implies that the effective isotropic viscosity in the bulk intergalactic plasma is suppressed by at least an order of magnitude, allowing turbulence to develop and transport energy from large to small scales. These observational results are consistent with the picture of plasma instabilities interacting with particles and/or with the establishment of a new type of turbulence that is immune to the local anisotropic viscosity.