Number 57, November 27, 1991 by Phillip F. Schewe and Ben Stein
A "ZEL'DOVICH PANCAKE," a massive protocluster of galaxies, may have been observed by radio astronomers at the Very Large Array in New Mexico. Named for the Russian astronomer Yakov B. Zel'dovich who pioneered the "top-down" theory of cosmology, these huge agglomerations of matter would have formed in the early universe from fluctuations in the density of matter; gravity would cause them to flatten into "pancakes." Later still these structures would fragment into galaxies. In contrast, the "bottom-down" theory holds that small structures such as galaxies come first followed by large structures such as galaxy clusters and superclusters. The new VLA observations have revealed a large radio-emitting object at a redshift of 3.4. The wavelength (21 cm) and narrow width of the emission line identify the source as being neutral hydrogen. The size, about 5 million light years across, and estimated mass, 3 x 1014 solar masses---suggest to Juan M. Uson and his colleagues Durgadas S. Bugri and Timothy J. Cornwell at the National Radio Astronomy Observatory that they are seeing evidence for a Zel'dovich Pancake. (Physical Review Letters, 9 December 1991.)
THE SOVIET-AMERICAN GALLIUM SOLAR NEUTRINO EXPERIMENT (SAGE) collaboration reports a neutrino capture rate of less than 79 solar neutrino units (1 SNU= 10-36 solar-neutrino captures per sec. per target atom), a rate less than that predicted (132 SNU) by the so-called Standard Solar Model. The SAGE detector, located at the Baksan Neutrino Observatory in the USSR, uses 30 tons of gallium to capture neutrinos produced inside the Sun during proton-proton fusion reactions. When the neutrinos reach the detector they will occasionally convert a gallium-71 nucleus into a germanium-71 nucleus. The level of extracted germanium therefore provides a measure of the incident solar neutrino flux. These first SAGE results are based on measurements carried out in January, February, March, April, and July 1990. The neutrino-flux shortfall seen in previous solar-neutrino experiments has prompted theorists to suggest either that the Sun was at fault (e.g., its core temperature was lower than we thought) or that neutrinos were at fault (e.g., neutrinos could transform from one type into another, fooling earthly detectors). The latter explanation is favored by the SAGE results since the rate for proton-proton fusion reactions is not dependent on the sun's core temperature. (A.I. Abazov et al., Physical Review Letters, 9 December 1991; for more information, contact Kenneth Lande, University of Pennsylvania, 215-898-8176.)
THE SMALLEST LASER YET , a thumbtack-shaped device only 2 microns across, has been developed by Sam McCall of AT&T Bell Labs. The business end of his microlaser is an indium-gallium-arsenide semiconductor disk only about 400 atoms thick. Light (at wavelengths of 1.3 to 1.5 microns) in the disk travels around the edge in a "whispering-gallery" mode, a process analogous to the travel of sound waves around the dome of a cathedral. (Science News, 23 November 1991.)
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