GETTING A PEEK AT BARE ELECTRONS . Modern quantum theory holds that the vacuum near an electron is filled with virtual particles blinking into and out of existence. Conservation of energy is not violated in this case because the particles live for such a short time, in accordance with the Heisenberg uncertainty principle. And just as it is difficult to view the surface of Venus because of its thick atmosphere, so a naked electron cannot easily be studied because of its self-made cloak of virtual particles. But physicists in Japan have now partly lifted the electron's veil. At the TRISTAN accelerator electrons and positrons collide head on. In these reactions events with the highest momentum-transferred- squared (Q^2) correspond to instances in which the electrons and positrons got very close to each other. Unlike the violent proton- antiproton collisions at Fermilab (where quarks and antiquarks approach to within 10^-19 m---see Update 299), the electron- positron collisions at TRISTAN do not involve the strong nuclear force, and thus the electron's unadulterated electromagnetic nature can be measured to an unprecedented extent. In the closest encounters---as close as 2 x 10^-18 m---the electrons and positrons could fairly be said to have partially penetrated each other's clouds. Thereby the TOPAZ detector collaboration (contact David Koltick of Purdue, koltick@physics.purdue.edu) has demonstrated, for the first time in a way that does not depend upon assumptions about the other forces of nature, that as expected the electromagnetic coupling constant, the parameter which specifies the inherent strength of the electromagnetic force, actually increases for very high- Q^2 events (up to values of 3337 (GeV/c)^2). (L. Levine et al., Physical Review Letters, 20 January 1997; see a figure at Physics News Graphics)

A BLACK HOLE'S EVENT HORIZON HAS BEEN DETECTED. Ramesh Naryan and his colleagues at the Harvard- Smithsonian Center for Astrophysics have used the orbiting ASCA x-ray telescope to study x-ray novas, binary systems in which gas from one star is pulled toward an accretion disk and the spherical region surrounding a compact companion. These systems occasionally flash prominently at x-ray wavelengths (hence the name x-ray nova), but Naryan is more interested in what happens during the quiescent intervals between upheavals. His recent theory, called the advection-dominated accretion flow (ADAF) model, suggests that if the accretion rate is slow enough the inspiraling gas will refrain from radiating away its accumulating energy. Instead the gas continues to get ever hotter, reaching temperatures as high as 10^12 K. Eventually this enormous energy buildup is dealt with in one of two ways: if the compact object is a neutron star, the gas will fall onto its surface, where it heats the star, causing it to radiate. In contrast, if the object is a black hole, there is no surface for the gas to fall upon; instead, like a prisoner being led to execution, the gas crosses the black hole's event horizon, never to be seen again. In effect, 99% of the gas energy disappears from the universe. Because of this, x-ray binaries containing a black hole should be dimmer than those with neutron stars. Naryan, speaking at this week's meeting of the American Astronomical Society in Toronto, reported on 9 binaries which fit the ADAF pattern of behavior. Four of these were thought to harbor black holes (because of their higher masses), and indeed these are all dimmer than the five neutron-star binaries. Naryan judges this dimness, and the binaries' x-ray spectra, to be the sign that an event horizon is at work, and that this in turn constitutes the most direct evidence yet for the existence of black holes.