Both the recently observed high runaway velocities of Cyg X-1 ( \sim 50 km s ^ { -1 } ) and X-ray Nova Sco 1994 ( \geq 100 km s ^ { -1 } ) and the relatively low radial velocities of the black hole X-ray binaries with low mass donor stars , can be explained by symmetric mass ejection in the supernovae ( SNe ) which formed the black holes in these systems .

Assuming symmetric mass ejection in black hole formation , we estimate the amount of mass that must have been ejected in the stellar core collapse in order to explain the velocities of the above X-ray binaries .
We find that at least 2.6 M _ { \odot } and 4.1 M _ { \odot } must have been ejected in the formation of Cyg X-1 and Nova Sco , respectively .
A similar mass loss fraction ( f = 0.35 ) for the black hole binaries with low mass donors , gives low velocities , in agreement with the observations .

We conclude that the black holes in X-ray binaries are all consistent with being formed in a successful SN in which mass is ejected .
A possible kick at the formation of the black hole is not needed to explain their space velocities .