Number 64, January 20, 1992 by Phillip F. Schewe and Ben Stein|
PLANETS AROUND PULSARS COME AND GO . Just as Alexander Wolszcan of Cornell was announcing the discovery of planets around the pulsar PSR 1257+12, Andrew G. Lyne of the University of Manchester was retracting his claim (made in July 1991) for a planet around pulsar PSR 1829-10. Lyne said, at last week's meeting of the American Astronomical Society in Atlanta, that the modulation of radio waves coming from PSR 1829-10 was caused not by the presence of a planet but was in fact an artifact of the Earth's motion around the Sun, a possibility that had been considered but then discounted in earlier studies of the data. "Our embarrassment is unbounded," Lyne had to admit to a sympathetic audience at the AAS meeting.
LOW SURFACE BRIGHTNESS GALAXIES have roughly the same mass, size, and shape (many have spiral arms) as ordinary "bright" galaxies, but emit only about one-tenth the amount of light, suggesting that much of their matter has not yet formed into stars. At the AAS meeting Stacy McGaugh of the University of Michigan and Patricia M. Knezek of the University of Massachusetts reported that many of the LSB galaxies tended to lie in less populated areas of the universe and that this relative lack of neighbors may account for the slower rate of star production. If this hypothesis is correct, Knezek asserts, the study of LSB galaxies might provide information about past eras of star formation in disk galaxies.
THE TOP QUARK MASS must be at least 91 GeV/c2, according to the Fermilab collaboration working at the colossal CDF detector. Studying pairs of leptons issuing from high energy proton-antiproton collisions, the CDF team did not find evidence for the top, which is expected to exist by the Standard Model of particle interactions, but they could affix the new lower limit on the top's mass. The previous CDF lower limit, published in 1990, was 77 GeV/c2. (F. Abe et al., 27 January 1992 issue of Physical Review Letters; this article lists 268 authors from 21 institutions.)
THE SMALLEST SUPERFLUID OBJECTS IN THE UNIVERSE are atomic nuclei, with their tightly-packed protons and neutrons able to slide over one another without friction. Scientists have tried to learn more about the superfluid nature of nuclei by studying the phenomenon of "backbending," which occurs when an excited nucleus, shedding its energy by emitting gamma rays, suddenly speeds up its spin for a brief time before slowing down. Recent experiments with heavy-ion colliders and nanosecond-resolution gamma detectors in Australia show evidence that the outermost neutron pair in the tungsten-179 nucleus becomes unpaired, aligns with the rotation of the nucleus, and causes a sort of phase change in which neutron pairs become uncoupled. As a result, the neutrons in the atoms lose their superfluidity and yet co-exist with protons still in a superfluid state. The researchers believe that similar effects may also be responsible for the periodic "glitches" in the rotation of pulsars, the largest known superfluid objects in the universe. (New Scientist, 11 January 1992.)