Number 25, March, 14 1991 by Phillip F. Schewe and Ben Stein|
NAKED SINGULARITIES PRESENT A PROBLEM FOR GENERAL RELATIVITY. Einstein's theory predicts that a gravitationally collapsing star of sufficient mass will eventually shrink within an "event horizon," inside of which the force of gravity is so great that even light cannot escape. At the heart of this black hole is a singularity, a point where gravity would be infinitely large and where the laws of physics would be problematic. Stuart L. Shapiro and Saul A. Teukolsky of Cornell have performed computer simulations (see Physical Review Letters, 25 Feb. 1991.) of collapsing, massive, elongated spheres which show that singularities can form without a surrounding black hole. These naked singularities cannot easily be incorporated in general relativity, according to Shapiro. (Science News, 9 Mar. 1991.)
FLUX LINES IN SUPERCONDUCTORS can now be imaged with electron holograms. One important application of superconductors is in magnets, where the movement of magnetic flux lines penetrating the superconductor can alter the critical current density. In an effort to study the lines' behavior, a method of imaging the lines was devised years ago in which ferromagnetic powder, sprinkled on the superconductor's surface, would line up in a characteristic pattern. Now a group of scientists at Hitachi in Japan (T. Matsuda et al., Phys. Rev. Lett., 28 Jan. 1991.) has succeeded in imaging the flux lines in a superconducting lead film by producing a holographic record on videotape at a rate of tens of frames per second; each hologram results from the interference between a reference electron wave and a wave whose phase has been altered, via the Aharonov-Bohm effect, by the flux lines. (Nature, 7 Mar. 1991.)
NEW GROUND-BASED TELESCOPES planned or under construction will quadruple the total light-gathering area available to astronomers using optical telescopes. Examples include the European Southern Observatory's Very Large Telescope (with a primary area of 210 m2) and the Keck Observatory (76 m2). Other factors which contribute to this surge in optical astronomy are adaptive optics, a dynamic mirror adjustment process which reduces the distortions caused by the blurring of light coming through the Earth's turbulent atmosphere, and solid-state detectors some 50 times more efficient than photographic plates. (Physics Today, Mar. 1991.)
THE MAGNETIC SUSCEPTIBILITY OF CARBON-60 has been measured by a team of scientists at AT&T Bell Labs and Cornell University. They found that the diamagnetism of C-60 is relatively small, implying that C-60 is an aromatic molecule: that is, its hexagonal facets are like a three-dimensional analog of a benzene ring. In contrast to the soccerball-shaped C-60, the egg-shaped C-70 molecule was found to be strongly diamagnetic. Thus the fullerenes as a family do not conform to a single aromatic category. (Nature, 7 Mar. 1991.)
CHARLES PETIT of the San Francisco Chronicle has won the 1991 AIP Science Writing Award to a journalist for his article, "Vanishingly Close to Absolute Zero," about research in the microkelvin regime (see Physics News Update 17, Jan. 17, 1991). Petit's article appeared in the Winter 1990/91 issue of Mosaic magazine.