Gravitational Lensing and Cosmic Strings

Abstract

Cosmic strings would be cosmologically interesting if they acted as seeds for rich cluster and galaxy formation. Most comological scenarios require the mean mass density per unit length of the string μ to be ∼ 2 × 10 −6 for cosmic strings to act as seeds. If there is a population of long-lived cosmic strings which are either long loops or infinite strings, then they will gravit ationally lense background sources (Vilenkin 1984). We are undertaking a substantial survey for multiply imaged optical quasars. So far we have examined ∼ 2500 quasars and have no candidate multiply imaged quasars with separations ≳ 13″ (Webster et aJ. 1987). This sample will double over the next year. The survey will detect multiply imaged quasars with the image separations predicted if one has a population of cosmic strings with μ ∼ 2 × 10 −6 acting as gravitational lenses. In due course, this survey will enable us to confirm or rule out the possibility that cosmic strings seed galaxy formation.