We study three processes that eject hypervelocity ( > 10 ^ { 3 } { km s ^ { -1 } } ) stars from the Galactic center : ( i ) close encounters of two single stars ; ( ii ) tidal breakup of binary stars by the central black hole , as originally proposed by Hills ; and ( iii ) three-body interactions between a star and a binary black hole ( BBH ) .
Mechanism ( i ) expels hypervelocity stars to the solar radius at a negligible rate , \sim 10 ^ { -11 } { yr } ^ { -1 } .
Mechanism ( ii ) expels hypervelocity stars at a rate \sim 10 ^ { -5 } ( \eta / 0.1 ) { yr } ^ { -1 } , where \eta is the fraction of stars in binaries with semimajor axis a _ { b } \lesssim 0.3 { AU } .
For solar-mass stars , the corresponding number of hypervelocity stars within the solar radius R _ { 0 } = 8 { kpc } is \sim 60 ( \eta / 0.1 ) ( a _ { b } / 0.1 { AU } ) ^ { 1 / 2 } .
For mechanism ( iii ) , { Sgr A ^ { * } } is assumed to be one component of a BBH .
We constrain the allowed parameter space ( semimajor axis , mass ratio ) of the BBH .
In the allowed region ( for example , semimajor axis of 0.5 \times 10 ^ { -3 } { pc } and mass ratio of 0.01 ) , the rate of ejecting hypervelocity stars can be as large as \sim 10 ^ { -4 } { yr } ^ { -1 } 
and the expected number of hypervelocity stars within the solar radius can be as large as \sim 10 ^ { 3 } .
Hypervelocity stars may be detectable by the next generation of large-scale optical surveys .