We construct a model for the formation of black holes within galactic bulges .
The initial state is a slowly rotating isothermal sphere , characterized by effective transport speed a _ { eff } and rotation rate \Omega .
The black hole mass is determined when the centrifugal radius of the collapse flow exceeds the capture radius of the central black hole .
This model reproduces the observed correlation between black hole masses and galactic velocity dispersions , { M _ { bh } } \approx 10 ^ { 8 } M _ { \odot } ( \sigma / 200 \hbox { km s } ^ { -1 } ) ^ { 4 } , where \sigma = \sqrt { 2 } a _ { eff } .
This model also predicts the ratio { \mu _ { B } } of black hole mass to host mass : { \mu _ { B } } \approx 0.004 ( \sigma / 200 \hbox { km s } ^ { -1 } ) .