A CENSUS OF LOW-MASS BLACK-HOLE BINARIES

The six known low mass black hole binaries discovered as X-ray/Optical novae represent a relatively uniform source class. It is shown that t he recurrence time for outbursts from these sources can be understood in the disk instability picture if magnetic braking is not active in t he short period systems. An extrapolation from the discovery surveys g ives an estimate of similar to 1700 such systems in the Galaxy as a wh ole. BATSE sky monitor observations should produce new candidate black hole transients at a rate of similar to 2/y. The population estimates also suggest that greater than or similar to 13 optical outbursts of black hole binaries prior to 1975 should have been recorded in classic al nova catalogues. Some strategies for discovery of more black hole b inaries are discussed.