DARK-MATTER AND NON-NEWTONIAN GRAVITY FROM GENERAL-RELATIVITY COUPLEDTO A FLUID OF STRINGS

An exact solution of Einstein's field equations for a point mass surro unded by a static, spherically symmetric fluid of strings is presented . The solution is singular at the origin. Near the string cloud limit there is a 1/r correction to Newton's force law. It is noted that at l arge distances and small accelerations, this law coincides with the ph enomenological force law invented by Milgrom in order to explain the f lat rotation curves of galaxies without introducing dark matter. When interpreted in the context of a cosmological model with a string fluid , the new solution naturally explains why the critical acceleration of Milgrom is of the same order of magnitude as the Hubble parameter.