|Description:|| In this talk I will explain the serendipitous discovery of the first known Be/black hole (BH) binary system, namely MWC 656, found after a possible gamma-ray flare detected by the AGILE satellite. I will discuss the importance of this discovery in the context of binary system evolution. In particular, I will comment on the Be/NS versus Be/BH ratio and I will show the possible evolution of MWC 656-like systems towards compact NS/BH systems that can merge and produce detectable gravitational waves in nearby galaxies.|
In addition, X-ray/radio observations have revealed counterparts in both energy ranges, providing evidence of a quiescent black hole in a high mass X-ray binary for the first time, which follows the accretion/ejection coupling already known from low mass X-ray binaries. These results show that the accretion/ejection coupling in stellar-mass BHs is independent of the nature of the donor star.
Finally, recent and ongoing observations show a long-term variability whose physical origin has to be understood.
I will review all these discoveries related to the first Be/BH system MWC 656 and will provide an outlook of the current observational efforts aimed at better understanding Be/BH systems.