The isotropic distribution function reads f ( x → → , v → → ) = 24 2 7 π π 3 a 2 G 5 M 0 4 ( − − E ( x → → , v → → ) ) 7 / 2 , if E < 0 , and f ( x → → , v → → ) = 0 otherwise, where E ( x → → , v → → ) = 1 2 v 2 + Φ Φ P ( r ) is the specific energy.