Tuning in on radio string.

Tuning in on radio string

A group of theoretical physicists and astronomers proposes using radio astronomy to look for defects in the geometry and topology of the universe that are left over from a previous cosmological epoch. The defects are known as cosmic strings (SN: 5/12/84, p. 294). This group of theorizers--E. M. Chudnovsky of Kharkov in the USSR, George B. Field and David N. Spergel of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and Alexander Vilenkin of Harvard University --suggests that cosmic strings may be at the heart of at least one recently discovered celestial radio source.

Certain recent cosmological theories propose that the universe went through one or more phase changes at certain crucial moments in its development. These phase changes are analogous to the sudden changes in the structures of substances when they freeze or melt. In the case of a universal phase change, it is not the arrangement of molecules or the bonds between them that change, but the geometrical characteristics of space and time themselves.

The cosmic phase changes are not uniform, however. They leave behind a few relics of the previous structure of spacetime in the form of long, thin strings. These strings move through the new structure of space-time at speeds near that of light.

Strings can have electromagnetic effects. Under certain conditions they can emit radio waves. Chudnovsky and his collaborators suggest that such radio sources should have a string-like appearance. A recently discovered radio source, G357.7 --0.1, has such an appearance and this group suggests it may be made of cosmic strings. The suggestion is easy to prove or refute, they say: If G357.7--0.1 is made of strings, its filaments should move at nearly light speed, and that should be observable in a very short time.