Plasma Instabilities and Magnetic Field Growth in Clusters of Galaxies

By A. Schekochihin, S. Cowley, R. Kulsrud, Gregory W. Hammett, Prateek Sharma. 2005

173 citations recorded by the source corpus.

We show that under very general conditions, cluster plasmas threaded by weak magnetic fields are subject to very fast growing plasma instabilities driven by the anisotropy of the plasma pressure (viscous stress) with respect to the local direction of the magnetic field. Such an anisotropy will naturally arise in any weakly magnetized plasma that has low collisionality and is subject to stirring. The magnetic field must be sufficiently weak for the instabilities to occur, viz., β ≳ Re1/2. The instabilities are captured by the extended MHD model with Braginskii viscosity. However, their growth rates are proportional to the wavenumber down to the ion gyroscale, so MHD equations with Braginskii viscosity are not well posed and a fully kinetic treatment is necessary. The instabilities can lead to magnetic fields in clusters being amplified from seed strength of ~10-18 G to dynamically important strengths of ~10 μG on cosmologically trivial timescales (~108 yr). The fields produced during the amplification stage are at scales much smaller than observed. Predicting the saturated field scale and structure will require a kinetic theory of magnetized cluster turbulence.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/cf685fd344b46534cb9910edff347bae45080451

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Citations in the corpus

Acceleration of primary and secondary particles in galaxy clusters by compressible MHD turbulence: from radio haloes to gamma-rays (2010, background): “It is known that the mean free path of thermal protons arising from Coulomb collisions in the hot IGM may be very large, ten to hundred kpc. Fluids in such a collisionless regime can be very different from their collisional counterparts (Schekochihin et al. 2005; 2010).”
ASTROPHYSICAL GYROKINETICS: KINETIC AND FLUID TURBULENT CASCADES IN MAGNETIZED WEAKLY COLLISIONAL PLASMAS (2007, background): “As was pointed out by Schekochihin et al. (2005), these are, in fact, an inevitable consequence of any large-scal fluid motions that change the strength of the magnetic field.”
Compressible turbulence in galaxy clusters: physics and stochastic particle re-acceleration (2007, background): “…important ingredient in the physics of the ICM as it is necessary to understand the amplification of magnetic fields in clusters (Dolag et al. 2002; Schekochihin et al. 2005; Subramanian et al. 2006), an issue closely related to the non–thermal emission from clusters but that we will not address…”
Evolving turbulence and magnetic fields in galaxy clusters (2005, background): “This prescription can be an oversimplification as it omits plausibly important physical effects arising from the anisotropy of viscosity in magnetized plasma (cf. Schekochihin et al. 2005b).”
Mechanical feedback from active galactic nuclei in galaxies, groups and clusters (2012, background): “Schekochihin et al (2005) argued that when the field is weak, pressure anisotropy due to fluid motions leads to fire hose or mirror instabilities that rapidly strengthen the field until the magnetic pressure is comparable to Re−1/2 p, where Re is the Reynolds number.”
Electron Heating in Hot Accretion Flows (2007, background): “This interplay of pressure anisotropy and microinstabilities is likely to be important in many other weakly collisional plasmas, e.g., the solar wind and X-ray clusters (e.g., Schekochihin et al. 2005).”