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Cosmic string - Definition and Overview |
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A cosmic string is a hypothetical 1-dimensional topological defect in the fabric of spacetime. Cosmic strings are hypothesized to form when different regions of spacetime undergo phase changes, resulting in domain boundaries between the two regions when they meet. This is somewhat analogous to the boundaries that form between crystal grains in solidifying liquids, or the cracks that form when water freezes into ice.
Cosmic strings, if they exist, would be extremely thin with diameters on the same order as a proton. They would have immense density, however, and so would represent significant gravitational sources. A cosmic string 1.6 kilometers in length would exert more gravity than the Earth. Cosmic strings would form a network of loops in the early universe, and their gravity could have been responsible for the original clumping of matter into galactic superclusters.
A cosmic string's vibrations, which are thought to oscillate near the speed of light, can cause part of the string to pinch off into an isolated loop. These loops have a finite lifespan due to decay via gravitational radiation. Today precison observations of the large sclae structure of the universe, directly using sky survey, or indirectly from observing the cosmic microwave background tend to rule out a significant rôle of cosmic strings.
Other types of topological defects in spacetime are domain walls, monopoles, and textures.
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