Evidence of a Massive Black Hole Companion in the Massive Eclipsing Binary V Puppis

Up to now, most stellar-mass black holes have been discovered in X-ray-emitting binaries, in which the black holes are formed through a common-envelope evolution. Here we give evidence for the presence of a massive black hole candidate as a tertiary companion in the massive eclipsing binary V Puppis. We found that the orbital period of this short-period binary (P = 1.45 days) shows a periodic variation while it undergoes a long-term increase. The cyclic period oscillation can be interpreted by the light-travel time effect via the presence of a third body with a mass of no less than 10.4 M_⊙. However, no spectral lines of the third body were discovered, which indicates that it is a massive black hole candidate. The black hole candidate may correspond to the weak X-ray source close to V Pup, discovered by the Uhuru, Copernicus, and ROSAT satellites, produced by accreting materials from the massive binary via a stellar wind. The circumstellar matter with many heavy elements around this binary may have been formed by the supernova explosion of the progenitor of the massive black hole. All of the observations suggest that a massive black hole is orbiting the massive close binary V Pup with a period of 5.47 yr. Meanwhile, we found that the central close binary is undergoing a slow mass transfer from the secondary to the primary star on a nuclear timescale of the secondary component, revealing that the system has passed through a rapid mass transfer stage.