Number 289, October 3, 1996 by Phillip F. Schewe and Ben Stein TeV-ENERGY GAMMA BURSTS from the galaxy Markarian 421, observed in May 1996, constitute the largest, purest flux of very high energy gamma rays yet recorded for an astronomical object. In one burst the flux increased above quiescent levels by a factor of 50 in an hour. A second burst 8 days later lasted only 30 minutes. The potency and brevity of such bursts (suggesting a source no larger than our solar system) provide new constraints on theories of energetic emissions from compact objects. The bursts were detected at the Whipple Observatory in Arizona, where air showers initiated by the incoming gammas show up as light in Cerenkov counters. (J.A. Gaidos et al., Nature, 26 September 1996.) QUARK-GLUON PLASMA is a hypothetical state of nuclear matter in which quarks and the gluons which normally bind the quarks into clumps of two quarks (mesons) or three quarks (baryons) would spill together in a seething soup analogous to the condition of ionized atoms in a plasma. Such a nuclear plasma may have existed in the very early universe and might exist again at accelerators if only physicists could sufficiently heat up ordinary nuclei by smashing them together. One of the products of these collisions (whether or not a plasma is formed) is psi mesons. Once hatched, the psi's must make their way out of the collision wreckage which, when two lead nuclei (each with more than 200 nucleons each) are involved, can be considerable. Preliminary results from the NA50 experiment at CERN indicate that only about half the expected psi's survive the journey (Science, 13 Sept.; Science News, 21 Sept.). Some theorists interpret this shortfall to meant that many psi's are being absorbed in a hotter-than-usual nuclear environment which might signify the presence of a quark-gluon plasma in at least part of the collision fireball. (Blaizot and Ollitrault, Phys. Rev. Lett., 26 Aug.) NANOROD-SUPERCONDUCTOR COMPOSITES might be able to carry high currents. One of the biggest obstacles to the greater application of high-temperature superconductors (HTSC) is that in the presence of large magnetic fields the bundles of magnetic flux lines within the superconductor begin to move about, causing energy dissipation and sometimes even the loss of the superconducting state. In an effort to pin the flux bundles in place, Harvard scientists Peidong Yang and Charles Lieber incorporate tiny defects in the form of magnesium oxide nanorods in their HTSC samples. The use of the nanorods increases the critical current, the maximum allowable current, by factors of up to 10 or more. The improvement in current density is highest for large fields and higher temperatures. Defects have been used before to control flux motion, but in previous experiments the defects were created by the use of heavy-ion or proton irradiation, a process which would be cumbersome if applied to commercial processing. (Science, 27 September 1996.) SOLAR NEUTRINO FLUXES VARY WITH A PERIOD OF 21.3 DAYS. This is the conclusion of Stanford scientists Peter Sturrock and Guenther Walther who examined years' of data from the Homestake (South Dakota), Kamiokande (Japan), and GALLEX (Italy) neutrino detectors. Hypothetical causes of the periodicity include the rotation of magnetic fields inside the sun or a variability in the production of neutrinos in the solar core. (Science, 20 Sept.; New Scientist, 21 Sept.)