  The hot, X-ray-emitting intracluster medium (ICM) is the dominant baryonic
constituent of clusters of galaxies. In the cores of many clusters, radiative
energy losses from the ICM occur on timescales significantly shorter than the
age of the system. Unchecked, this cooling would lead to massive accumulations
of cold gas and vigorous star formation, in contradiction to observations.
Various sources of energy capable of compensating these cooling losses have
been proposed, the most promising being heating by the supermassive black holes
in the central galaxies through inflation of bubbles of relativistic plasma.
Regardless of the original source of energy, the question of how this energy is
transferred to the ICM has remained open. Here we present a plausible solution
to this question based on deep Chandra X-ray observatory data and a new
data-analysis method that enables us to evaluate directly the ICM heating rate
due to the dissipation of turbulence. We find that turbulent heating is
sufficient to offset radiative cooling and indeed appears to balance it locally
at each radius - it might therefore be the key element in resolving the gas
cooling problem in cluster cores and, more universally, in atmospheres of X-ray
gas-rich systems.
