Number 42, July 24, 1991 by Phillip F. Schewe and Ben Stein|
A PLANET HAS BEEN DISCOVERED AROUND A NEARBY PULSAR , according to an advance summary of the July 25 issue of Nature. British radio astronomers at Jodrell Bank, the summary says, report that the planet has 10 times the mass of Earth and travels in a 182-day orbit around the pulsar at a radius equivalent to that of Venus about the Sun.
INDIVIDUAL STARS IN THE GALAXY NGC4571 HAVE BEEN RESOLVED with the Canada-Hawaii-France Telescope on Mauna Kea. These are the most distant single stars ever seen. Astronomers Robert McClure (604-388-0021) and Michael Pierce of the Dominion Astrophysical Observatory in Victoria, Canada use the apparent spacing of the stars and their brightness to calculate a value for the distance between Earth and the Virgo cluster (in which NGC4571 resides) of 50 million light years, which in turn implies a Hubble constant of about 85. This value, rather high as Hubble constant estimates go, further complicates the general effort to establish a consistent cosmic yardstick. Astronomers hope that a rejuvenated Hubble Space Telescope, with its keen resolution brought into play through corrective optics, may elucidate the matter by looking at single stars in many galaxies. (Science, 12 July 1991.)
TEN NEW MILLISECOND PULSARS have been discovered in a single globular cluster by an Australian-British-Italian team. There were only 13 known pulsars of this type, scattered in 12 other globular clusters, prior to this discovery. These pulsars, 13,000 light years away in cluster 47 Tucanae, spin so fast that they complete revolutions in milliseconds and spew radio pulses and other types of radiation at precisely-timed intervals. Because they are extremely sensitive to gravitational forces, the pulsars are expected to provide insight into the composition of the globular cluster's core, believed to be composed of old neutron stars. Indeed, millisecond pulsars are believed to form when a dying neutron star is given new life---and sped up considerably---by matter drifting in from a lighter stellar neighbor. But only one of these star systems has been detected in 47 Tucanae, casting doubt on this explanation, or at the very least setting relatively short life spans for these suspected precursors of the pulsar. (Nature, 18 July 1991.)
SILICON ATOMS, DESPITE THEIR TIGHT COVALENT BONDS , can now be manipulated with scanning tunneling microscopes. In a mechanism known as field evaporation, silicon ions rise up to the STM's tip as a result of both the strong electric fields set up by the STM and the chemical interactions between the tip and the sample. In-Whan Lyo and Phaedon Avouris of IBM report that at longer tip-sample distances a mound of atoms forms a bridge between the silicon surface and the STM tip; clusters of atoms can then be removed, leaving behind a gaping hole. At shorter tip-sample distances, individual atoms can be removed, but with less reproducible results. By reversing the polarity of the voltage, the atoms can be re-deposited anywhere on the silicon surface. This new process promises many applications, including the fabrication of new semiconductors and the creation of locally-doped silicon materials. (Science, 12 July 1991.)