  Hyper-velocity stars (HVSs) were first predicted by theory to be the result
of the tidal disruption of a binary system by a super-massive black hole (SMBH)
that accelerates one component to beyond the Galactic escape velocity (the
Hills mechanism). Because the Galactic centre hosts such a SMBH it is the
suggested place of origin for HVSs. However, the SMBH paradigm has been
challenged recently by the young HVS HD271791 because its kinematics point to a
birthplace in the metal-poor rim of the Galactic disc. Here we report the
atmosphere of HD271791 to indeed show a sub-solar iron abundance along with an
enhancement of the alpha-elements, indicating capture of nucleosynthesis
products from a supernova or a more energetic hypernova. This implies that
HD271791 is the surviving secondary of a massive binary system disrupted in a
supernova explosion. No such run-away star has ever been found to exceed the
Galactic escape velocity, hence HD271791 is the first hyper-runaway star. Such
a run-away scenario is an alternative to the Hills mechanism for the
acceleration of some HVSs with moderate velocities. The observed chemical
composition of HD271791 puts invaluable observational constraints on
nucleosynthesis in a supernova from the core-collapse of a very massive star
(M_ZAMS >= 55 M_Sun), which may be observed as a gamma-ray burst of the
long-duration/soft-spectrum type.
