Fifty years ago, borrowing an idea from our Russian friends Guseinov and Zeldovich, we looked for very compact stars (neutron stars and black holes, in modern terminology) as optically-invisible components of single-line spectroscopic binaries. We didn't find any, but our method was very close to the processes that soon identified neutron stars in the X-ray sources Sco X-1, Cen X-3, and so forth, and the first persuasive black hole in Cyg X-1 (HD 226868). Here we look again at the events of 1962-72, revealing a bit more than we knew then, and attempt to bring the story up to date with an overview of some of the enormous richness of astronomical sources now generally thought to consist of a neutron star or black hole, or in a few cases one of each in a binary system.

To be published in Cz\k{e}stochowski Kalendarz Astronomiczny 2019, B. Wszolek and A. Ku\'zmicz editors, Cz\k{e}stochowa, Poland