Black Holes and Binary Stars

Abstract

Gibbons and Hawking1 have suggested that a number of spectroscopic binaries contain black holes. The formation of a black hole in a binary system would be accompanied by a sudden loss of mass from the system, and they believe that this mass loss could convert an initially circular orbit into an appreciably elliptical one. Only masses greater than 1.4 M⊙ can collapse into black holes, and normal double-line spectroscopic binaries cannot contain black holes, so Gibbons and Hawking investigate those single-line spectroscopic binaries listed in the Sixth Catalogue2 for which they estimate that each component has a mass greater than 1.4 M⊙. There are only seven such systems, three of which have orbital eccentricities greater than 0.08. On the other hand, there are 55 double-line systems in which both components are more massive than 1.4 M⊙, and eight of these have orbital eccentricities greater than 0.08. Comparing the relative numbers of eccentric and circular orbits in these two rather small samples, Gibbons and Hawking conclude that there is an excessive number of eccentric orbits among single-line spectroscopic binaries, and that the formation of black holes in some of the systems may have produced this excess. Specifically, they suggest that HD 176318, HD 184035 (201 G Sgr), and HD 194495 may contain black holes.