Stopping Cooling Flows with Cosmic Ray Feedback
  Multi-Gyr two-dimensional calculations describe the gasdynamical evolution of
hot gas in the Virgo cluster resulting from intermittent cavities formed with
cosmic rays. Without cosmic rays, the gas evolves into a cooling flow,
depositing about 85 solar masses per year of cold gas in the cluster core --
such uninhibited cooling conflicts with X-ray spectra and many other
observations. When cosmic rays are produced or deposited 10 kpc from the
cluster center in bursts of about 10^{59} ergs lasting 20 Myrs and spaced at
intervals of 200 Myrs, the central cooling rate is greatly reduced to 0.1 - 1
solar masses per year, consistent with observations. After cosmic rays diffuse
through the cavity walls, the ambient gas density is reduced and is buoyantly
transported 30-70 kpc out into the cluster. Cosmic rays do not directly heat
the gas and the modest shock heating around young cavities is offset by global
cooling as the cluster gas expands. After several Gyrs the hot gas density and
temperature profiles remain similar to those observed, provided the
time-averaged cosmic ray luminosity is about 10^{43} erg/s, approximately equal
to the bolometric X-ray luminosity within only 56 kpc. If an appreciable
fraction of the relativistic cosmic rays are protons, gamma rays produced by
pion decay following inelastic p-p collisions may be detected with the Fermi
Gamma Ray Telescope.
