  We report the discovery of a symmetric bow shock around the well-known
high-mass X-ray binary (HMXB) Vela X-1. Wind bow shocks are a ubiquitous
phenomenon around OB-runaway stars, but now such a structure is found around a
HMXB. The presence of a bow shock indicates that the system has a high
(supersonic) velocity with respect to the interstellar medium. From the
symmetry of the bow shock, the direction of motion and, moreover, the origin
and age of the system can be derived. Our observation supports Blaauw's
scenario for the formation of an OB-runaway star by the supernova explosion of
the binary companion.
