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 { \dot { M } } \approx 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 L _ { cr } = 2.7 \times 10 ^ { 43 } erg s ^ { -1 } , approximately equal to the bolometric cooling rate L _ { X } within only \sim 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 .