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Stringing out a cosmic image, perhaps.

Stringing out a cosmic image, perhaps

A cosmic string is a relic of the cosmic past, an isolated region where the way things used to be persists, where the density (4 10(23) grams per centimeter) and geometric characteristics of a previous eon survive (SN:5/12/84, p. 294). In a newly discovered gravitational lens effect, some astronomers believe they may have found a cosmic string.

A gravitational lens effect (GLE) is a double image of a single quasar, produced by the bending of the quasar's light by some massive object. The newly found GLE has a much wider spread between the images than any of the others, 2.6 minutes of arc, which indicates that the object doing the lensing is exotic: a massive cluster of galaxies, a supermassive black hole (10(15) times the sun's mass) or a cosmic string.

The finding is part of a search for cosmic strings, J. Richard Gott of Princeton (N.J.) University told SCIENCE NEWS. Gott had predicted that strings should produce GLEs with widely separated images. Another Princeton astronomer, Bohdan Paczynski, had searched records for such wide pairs. Quasar pair 1146 111B, C was on the list he published. Edwin L. Turner of Princeton and six others took spectra of those images and showed that they meet the criteria for a GLE, they report in the May 8 NATURE.

Strings should make double images, Gott says, because they render space-time cone-shaped. (We are at the apex of the cone looking to the base.) Light from any distant point must follow the surface of the cone, and in so doing takes two paths, giving two images. This doubling can be illustrated by flattening the cone after making a cut up the side from the distant point to the apex. One gets a "PACMAN shape,' Gott says, a circle with a wedge cut in it. The sides of the wedge make two different paths from the apex to what is really only one point on the base.

A cluster of galaxies should give three images, so one test is to look for a third image. A black hole would give two images, but it would have to be exactly between them, and it should give symmetrically placed doublings of other quasars within the 2.6-minute circle. A point in favor of a string, says Gott, is that the images are equally bright and seem to be too faint to be much magnified. A cluster or a black hole would magnify them.

A string should make a difference in our perception of the temperature of the cosmic microwave background radiation on opposite sides of it. Looking for such a variation, Anthony Stark, Mark, Dragovan and Robert L. Wilson of AT&T Bell Labs in Holmdel, N.J., and Gott have made a radio map of the area. The result is inconclusive, but they hope to do better next year. On the other hand, they did not find the expected evidence for a cluster:a drop of 3 millikelvins due to gas in the cluster.

All in all, Gott does not expect the question to be settled quickly or easily. It will take a painstaking examination of everything in that 2.6-minute circle--a huge field to astronomers--looking for multiple images and other effects of the different possible lensing agents.
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Author:Thomsen, Dietrick E.
Publication:Science News
Date:May 17, 1986
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