Number 69 (Story #4), February 27, 1992 by Phillip F. Schewe and Ben Stein BLACK HOLE CANDIDATES are becoming more numerous. Besides the telltale bursts of x rays, the chief evidence for black-hole status seems to be the estimation of a mass of three or more solar masses for the unseen partner of a binary pair; this criterion rules out neutron stars, which must have lower masses. V404 Cygni, Nova Musca, and A0620 are the names of some the heavier contenders. None of these, of course, are in the same league with those million-solar-mass black holes suspected of living at the heart of certain active galaxies. (Astronomy, Mar. 1992; Science, 14 Feb. 1992.)