Number 50 (Story #5), October 3, 1991 by Phillip F. Schewe and Ben Stein SS433 IS NOT A BLACK HOLE , but rather a neutron star, assert scientists at the European Southern Observatory. First discovered in 1977, SS433 has been of great astronomical interest since its optical spectrum indicated the presence of hydrogen atoms moving at extremely high velocities. Some astronomers hypothesized that SS433 was a miniature version (right here in our galaxy) of the sort of energy engine---possibly a black hole---thought to drive active galaxies and quasars. The new ESO measurements indicate that SS433's mass is less than that of our sun and that therefore it cannot be a black hole. (ESO news release, 24 Sept. 1991.)