Department of Physics & Astronomy

Spring 2009 Colloquia


Eliot Quataert

Eliot Quataert

Department of Astronomy
University of Califronia, Berkeley
New Forms of Convection in Galaxy Cluster Plasmas: How do Galaxy Clusters Boil?
February 23, 2009, 4PM, Thornton 411

Galaxy clusters are among the largest gravitationally bound objects in the universe. The majority of the baryonic mass in clusters resides in a hot, low density plasma that pervades the intracluster medium. The heating and cooling processes in galaxy cluster plasmas must be understood in order to make progress on a number of key problems in galaxy formation, including the formation of the most massive galaxies and black holes in the universe. An understanding of galaxy cluster thermodynamics is also important for the use of clusters as cosmological probes into the nature of dark matter and dark energy. Electron thermal conduction in cluster plasmas transports heat primarily along (but not across) magnetic field lines. Remarkably, convection in the presence of anisotropic heat conduction is fundamentally different from the familiar convection in stellar interiors: for a weak magnetic field, a plasma is convectively unstable regardless of the sign of the temperature gradient. Thus the entire intracluster medium in galaxy clusters is convectively unstable! In this talk, I will describe the physics of these convective instabilities and the results of nonlinear simulations studying their implications for galaxy cluster plasmas. I will also describe the importance of instabilities triggered by relativistic particles (produced by a central AGN) rather than by the thermal plasma.

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