Physics – Plasma Physics
Scientific paper
Oct 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aps..dppli2005c&link_type=abstract
American Physical Society, 43rd Annual Meeting of the APS Division of Plasma Physics October 29 - November 2, 2001 Long Beach, C
Physics
Plasma Physics
Scientific paper
Galaxy clusters are the largest gravitationally bound structures in the universe. A typical cluster contains around 1000 galaxies and an enormous amount of diffuse hot plasma filling the space between galaxies. Over the last two decades, observations have led to a controversy in the astronomical community over the evolution of galaxy-cluster plasmas. On the one hand, x-ray observations have led many astronomers to embrace the ``cooling-flow'' model in which vast quantities of plasma cool and flow inwards towards a cluster's center, presumably forming stars and possibly smaller compact objects. On the other hand, radio, optical, and ultraviolet observations have placed strict upper limits on the numbers of ordinary-sized stars forming at the centers of galaxy clusters, thereby leading many astronomers to suspect that intracluster plasmas do not cool and flow inwards at anywhere near the rates predicted by the cooling-flow model. One of the biggest obstacles to the resolution of this controversy is the uncertainty in the heating rate in a cluster's core where most of the radiative cooling is taking place. The most important potential heat source is conduction of heat into the relatively cooler central region from the hotter surrounding plasma. If the thermal conductivity κT is comparable to the Spitzer value κS for a non-magnetized gas, then conductive heating overwhelms radiative cooling and the cooling-flow model is invalid. In order for the cooling-flow model to work, κT must be less than approximately 10-2κ_S. The best candidate for suppressing κT is the tangled magnetic-field structure observed in intracluster plasmas. In this talk I will review the phenomenology of heat conduction in a tangled magnetic field and what it tells us about the cooling-flow model.
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