  The level of random motions in the intracluster gas lying between 20 and 60
kpc radius in the core of the Perseus cluster has been measured by the Hitomi
Soft X-ray Spectrometer at 164 +/- 10 km/s. The maximum energy density in
turbulent motions on that scale is therefore low. If dissipated as heat the
turbulent energy will be radiated away in less than 80 Myr and cannot spread
across the core. A higher velocity is needed to prevent a cooling collapse.
Gravity waves are shown to travel too slowly in a radial direction. Here we
investigate propagation of energy by sound waves. The energy travels at about
1000 km/s and can cross the core in a cooling time. We show that the
displacement velocity amplitude of the gas required to carry the power is
consistent with the Hitomi result and that the inferred density and temperature
variations are consistent with Chandra observations.
