Radiation, winds, and jets from the active nucleus of a massive galaxy can interact with its interstellar medium, and this can lead to ejection or heating of the gas. This terminates star formation in the galaxy and stifles accretion onto the black hole. Such active galactic nuclei (AGN) feedback can account for the observed proportionality between the central black hole and the host galaxy mass. Direct observational evidence for the radiative or quasar mode of feedback, which occurs when AGN are very luminous, has been difficult to obtain but is accumulating from a few exceptional objects. Feedback from the kinetic or radio mode, which uses the mechanical energy of radio-emitting jets often seen when AGN are operating at a lower level, is common in massive elliptical galaxies. This mode is well observed directly through X-ray observations of the central galaxies of cool core clusters in the form of bubbles in the hot surrounding medium. The energy flow, which is roughly continuous, heats the hot intraclu...

Observational Evidence of Active Galactic Nuclei Feedback

A comprehensive review of zonal flow phenomena in plasmas is presented. While the emphasis is on zonal flows in laboratory plasmas, planetary zonal flows are discussed as well. The review presents the status of theory, numerical simulation and experiments relevant to zonal flows. The emphasis is on developing an integrated understanding of the dynamics of drift wave–zonal flow turbulence by combining detailed studies of the generation of zonal flows by drift waves, the back-interaction of zonal flows on the drift waves, and the various feedback loops by which the system regulates and organizes itself. The implications of zonal flow phenomena for confinement in, and the phenomena of fusion devices are discussed. Special attention is given to the comparison of experiment with theory and to identifying directions for progress in future research.

/pdf/zonal-flows-in-plasma-a-review-3byloag115.pdf

Zonal flows in plasma—a review

Astrophysical magnetic fields and nonlinear dynamo theory

Advanced Mathematical Methods for Scientists and Engineers

▪ Abstract Turbulence affects the structure and motions of nearly all temperature and density regimes in the interstellar gas. This two-part review summarizes the observations, theory, and simulations of interstellar turbulence and their implications for many fields of astrophysics. The first part begins with diagnostics for turbulence that have been applied to the cool interstellar medium and highlights their main results. The energy sources for interstellar turbulence are then summarized along with numerical estimates for their power input. Supernovae and superbubbles dominate the total power, but many other sources spanning a large range of scales, from swing-amplified gravitational instabilities to cosmic ray streaming, all contribute in some way. Turbulence theory is considered in detail, including the basic fluid equations, solenoidal and compressible modes, global inviscid quadratic invariants, scaling arguments for the power spectrum, phenomenological models for the scaling of higher-order structu...

http://www.ifa.hawaii.edu/%7Ereipurth/reviews/elmegreen1_araa.pdf

Interstellar Turbulence I: Observations and Processes

This is a brief account of our numerical study of the tearing mode reconnection. We demonstrate two main points. First, we show that, given sufficiently small resistivity, the Rutherford regime always exists; larger values of Delta' require smaller values of resistivity. Rutherford's negligible-inertia assumption is validated and the asymptotically linear dependence of the time derivative of the island width on the resistivity and Delta' is confirmed. Second, we find that, at large Delta', the Rutherford regime is followed by a nonlinear stage of fast growth linked to X-point collapse and formation of a current sheet. This causes the reconnection to become Sweet-Parke (SP) like. The signature resistivity^{1/2} scaling of the effective island growth rate is, indeed, found in this nonlinear stage. The SP stage culminates in the saturation of the mode, which can, thus, be achieved much faster than via Rutherford regime.

Fast and Slow Nonlinear Tearing Mode Reconnection

Introduction Magnetic reconnection is a plasma physics phenomenon whereupon magnetic field lines which are being convected with the flows in the plasma suddenly break and reconnect in a different configuration. Magnetic energy is released in this process, giving rise to high velocity plasma flows, energetic particles and plasma heating. Reconnection is widely believed to be the cause of solar flares; it is also manifest in the interaction between the solar wind and the Earth’s magnetic field in the magnetopause and magnetotail. In fusion devices it plays a crucial role in the development of the sawtooth instability, which has potentially disastrous consequences to the plasma confinement. In many plasmas of interest it has long been suspected that an MHD description is too simple to fully explain the complexity of the observations. The discrepancy is obvious in the observed and calculated reconnection rates which, in the MHD framework, differ by several orders of magnitude. Interest has diverged to non-MHD effects which might cause a speed-up of this process. The potential candidates differ depending on the specific geometry and plasma parameters. For example, in most present fusion plasmas, the ion Larmor radius should exceed, or at least be comparable to, the width of the dissipation region. Thus, ion finite Larmor radius (FLR) effects cannot be neglected and are, in fact, known to produce a speed up of the reconnection rate [1]. From the numerical point of view, the FLR terms bring about one further complication: they introduce the Kinetic Alfven wave (KAW) into the system, which has a dispersive character, i.e., ω ∼ k ⊥ (the counterpart to this in the absence of a strong magnetic field is the Hall term in Ohm’s law, which also introduces a dispersive wave, the whistler). Explicit numerical integration schemes show great difficulties in coping with this wave, the time step being thus set to an impractically low value. Building on previous work [2, 3] we present a new semi-implicit method that stabilizes the KAW and the Alfven wave (AW), while remaining accurate in the linear and nonlinear regimes. Timestep enhancements over the CFL condition of ∼ 100 are obtained. Comparison with a fully explicit calculation is presented and preliminary linear and nonlinear results are briefly discussed.

Steven Cowley

Papers

Fast and Slow Nonlinear Tearing Mode Reconnection

FLR effects in nonlinear tearing mode reconnection