Runaway cosmic strings

Abstract

Cosmic strings are now established as a possible mechanism for forming galaxies and clusters in the Universe (refs 1–4; H. Sato, preprint HUNS 827, Kyoto University, 1986). Much recent work has been devoted to calculating the behaviour of strings and their interaction with matter in an effort to understand better the special features of the string model. Here, I examine two effects which have been neglected in many treatments but which could, it appears, alter certain details of our picture of string-induced galaxy formation. First, loops of cosmic string behave like relativistic gyroscopes, and undergo only a very slow precession under the influence of newtonian gravitational torques. They thus impose a 'stiff time-averaged quadrupolar gravitational potential on matter in their vicinity. Second, the gravitational radiation beamed by an oscillating loop probably has a significant component of dipole asymmetry when averaged over the loop decay time. Recoil reaction on the loop causes a coherent acceleration over time and eventually leads to a high peculiar velocity when loops decay. String loops today would then not generally be found in the centres of galaxies and clusters, but flying freely through intergalactic space.