Suppressed effective viscosity in the bulk intergalactic plasma. (arXiv:1906.06346v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zhuravleva_I/0/1/0/all/0/1">I. Zhuravleva</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Churazov_E/0/1/0/all/0/1">E. Churazov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schekochihin_A/0/1/0/all/0/1">A. A. Schekochihin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Allen_S/0/1/0/all/0/1">S. W. Allen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vikhlinin_A/0/1/0/all/0/1">A. Vikhlinin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Werner_N/0/1/0/all/0/1">N. Werner</a>
Transport properties, such as viscosity and thermal conduction, of the hot
intergalactic plasma in clusters of galaxies, are largely unknown. While for
laboratory plasmas these characteristics are derived from the gas density and
temperature, such recipes can be fundamentally different for the intergalactic
plasma due to a low rate of particle collisions and a weak magnetic field. In
numerical simulations, one often cuts through these unknowns by modeling these
plasmas as hydrodynamic fluids, even though local, non-hydrodynamic features
observed in clusters contradict this assumption. Using deep Chandra
observations of the Coma Cluster, we probe gas fluctuations in intergalactic
medium down to spatial scales where the transport processes should prominently
manifest themselves – at least if hydrodynamic models with pure Coulomb
collision rates were indeed adequate. We find that they do not, implying that
the effective isotropic viscosity is orders of magnitude smaller than naively
expected. This indicates an enhanced collision rate in the plasma due to
particle scattering off microfluctuations caused by plasma instabilities, or
that the transport processes are anisotropic with respect to local magnetic
field. For that reason, numerical models with high Reynolds number appear more
consistent with observations. Our results also demonstrate that observations of
turbulence in clusters are becoming a branch of astrophysics that can sharpen
theoretical views on such plasmas.
Transport properties, such as viscosity and thermal conduction, of the hot
intergalactic plasma in clusters of galaxies, are largely unknown. While for
laboratory plasmas these characteristics are derived from the gas density and
temperature, such recipes can be fundamentally different for the intergalactic
plasma due to a low rate of particle collisions and a weak magnetic field. In
numerical simulations, one often cuts through these unknowns by modeling these
plasmas as hydrodynamic fluids, even though local, non-hydrodynamic features
observed in clusters contradict this assumption. Using deep Chandra
observations of the Coma Cluster, we probe gas fluctuations in intergalactic
medium down to spatial scales where the transport processes should prominently
manifest themselves – at least if hydrodynamic models with pure Coulomb
collision rates were indeed adequate. We find that they do not, implying that
the effective isotropic viscosity is orders of magnitude smaller than naively
expected. This indicates an enhanced collision rate in the plasma due to
particle scattering off microfluctuations caused by plasma instabilities, or
that the transport processes are anisotropic with respect to local magnetic
field. For that reason, numerical models with high Reynolds number appear more
consistent with observations. Our results also demonstrate that observations of
turbulence in clusters are becoming a branch of astrophysics that can sharpen
theoretical views on such plasmas.
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