Abstract
A solution for cosmological expansion in the presence of dark matter is presented, and observational results from which a conclusion on the present value of the cosmological constant is obtained, are discussed. A solution is obtained for hydrodynamic outflow of polytropic gas from a gravitating center, in the presence of uniform Dark Energy (DE). The antigravity of DE is enlightening the outflow and makes the outflow possible at smaller initial temperature at the same density. The main property of the wind in the presence of DE is its unlimited acceleration after passing the critical point. Applying this solution to winds from galaxy clusters, we suggest that a collision of a strongly accelerated wind with another galaxy cluster, or with another galactic cluster wind, could lead to the formation of highest energy cosmic rays.
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