Number 34 (Story #1), May 15, 1991 by Phillip F. Schewe and Ben Stein THE GREAT ANNIHILATOR , the powerful source of gamma rays (from electron-positron annihilation) near, but not at, the galactic center, has dimmed by two thirds from its peak brightness recorded last October, according to scientists working with the French-Soviet satellite GRANAT. Independent observations at radio, microwave, and x-ray wavelengths are zeroing in on the location of the source. (Science News, 11 May.)