Cosmological accretion wakes

In an expanding universe, a rapidly moving cosmic string or point mass causes matter to accrete into a wake behind the perturber. Analytic solutions for the structure and evolution of these wakes are derived using the Zel'dovich approximation. At early times the wakes are narrow and their evolution is self-similar. It is found that the amount of mass accreted into the wake of a point mass or small loop of cosmic string is approximately independent of the peculiar velocity of the perturber, so that the spherical accretion model correctly gives the mass that has become nonlinear. Initially the accretion wake of a moving point mass is a thin cylinder, but it becomes increasingly spherical as matter is accreted from larger comoving volumes. The accretion wakes of long strings have the form of thin sheets. Less matter is swept up in the sheets than in the wakes of small loops, but the long strings may be important for large-scale structure. The cosmic string scenario of structure formation predicts that galaxy halos should be nearly round, while Abell clusters should be prolate. 22 references.