The quest for collapsed/frozen stars in single-line spectroscopic binary systems

Black holes are now commonplace, among the stars, in Galactic centers, and perhaps other places. But within living memory, their very existence was doubted by many, and few chose to look for them. Zeldovich and Guseinov were first, followed by Trimble and Thorne, using a method that would have identified HDE 226868 as a plausible candidate, if it had been in the 1968 catalogue of spectroscopic binaries. That it was not arose from an unhappy accident in the observing program of Daniel M. Popper long before the discovery of X-ray binaries and the identification of Cygnus X-1 with that hot, massive star and its collapsed companion.
Comment: Key Words: Black holes, collapsed stars, Cygnus X-1, HDE 226868, spectroscopic binaries Journal: The Zeldovich Universe Genesis and Growth of the Cosmic Web IAU Symposium 308, 23-28 June 2014, Tallinn, Estonia) http://iau.maido.ee/proceedings