A NEW CELESTIAL SOURCE OF POSITRONS has been identified. Positrons (antielectrons) are routinely made on Earth at several labs (SLAC, LEP, HERA) and in deep space (the galactic center and cosmic rays). The Gamma Ray Observatory (GRO) has now found a new positron source. At a meeting in Williamsburg, VA yesterday, GRO scientists announced the observation of a diffuse fountain of positron-emitting material projecting 3000 light years out of the plane of our galaxy. The researchers are happy to have found a new galactic feature but are puzzled as to why the flare, starting near or at the core of the Milky Way, flows north out of the plane but not south. (See figure at Naval Research Laboratory web site)

SOUND WAVES AND SUPERNOVAS IN BOSE-EINSTEIN CONDENSATES (BECs). Since 1995, scientists have been creating the BEC state, in which a cloud of atoms is cooled to near-absolute-zero temperatures, falling into the same quantum state and acting as a single entity (Update 233). At this month's APS/AAPT meeting in Washington, three researchers spoke on this subject. (1) Randy Hulet of Rice University reported that BECs of lithium atoms--different from other BECs in that the lithium atoms attract rather than repel each other--are limited to a size of approximately 1500 atoms. According to some predictions, adding more atoms than this would cause the BEC to undergo a "macroscopic quantum tunneling" in which the condensate would collectively transform from a low-density to a high-density state, forming molecules which would then release excess heat and cause the BEC to blow apart like a supernova. (2) Studying BECs of rubidium atoms, Eric Cornell of NIST and the University of Colorado discussed experiments confirming that BECs are significantly more uniform in density than comparable clouds of cold atoms in a non-BEC state. (3) Using laser light to excite a specific spot on his cigar-shaped BEC of sodium atoms, Wolfgang Ketterle of MIT described how the resulting disturbance in a typical condensate propagates at about 5 millimeters per second, roughly 70,000 times slower than the speed of sound in air. (Writeup and figure from Hulet's group at APS Virtual Pressroom)

ONE HUNDRED YEARS OF ELECTRONS. On April 30, 1897, at a meeting of the Royal Institution in London, physicist Joseph John (J.J.) Thomson declared that cathode rays lighting up a fluorescent screen were made of negatively charged particles. Thomson boldly proclaimed that these particles--which we now know as electrons--could be found in all atoms. The term "electron" as it applied to electricity actually came about in 1891 to describe the unit of electric charge in a chemical reaction. The electron was the first known subatomic corpsucle and its discovery marks the advent of particle physics. Michael Riordan (editor of SLAC Beamline, whose Spring 1997 issue is devoted to the electron centennial) refers to the electron as a truly "industrial strength" particle, since it is the workhorse of electronics, including television, telephones, and personal computers. (Many of these devices organize electrons inside transistors which were themselves developed exactly half a century ago.) Labor saving devices aside, electrons are of course the outer constitutents of all atoms and the principal currency of exchange in all chemical reactions. (See also the AIP History Center's web exhibit)