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Where Are the Be/Black Hole Binaries?

We apply the tidal truncation model proposed by Negueruela and Okazaki to arbitrary Be/compact star binaries to study the dependence of the truncation efficiency on the binary parameters. We find that the viscous decretion disks around the Be stars can be truncated very effectively in narrow systems. Combining this with the population synthesis results of Podsiadlowski, Rappaport, and Han which state that binary black holes are most likely to be born in systems with orbital periods less than about 30 days, we suggest that most of the Be/black hole binaries may be transient systems with a very long quiescent state. This could explain the lack of observed Be/black hole X-ray binaries. We also discuss the evolution of the Be/black hole binaries and their possible observational features.