  We calculate axion radiation emitted in the collision of two straight global
strings. The strings are supposed to be in the unexcited ground state, to be
inclined with respect to each other, and to move in parallel planes. Radiation
arises when the point of minimal separation between the strings moves faster
than light. This effect exhibits a typical Cerenkov nature. Surprisingly, it
allows an alternative interpretation as bremsstrahlung under a collision of
point charges in 2+1 electrodynamics. This can be demonstrated by suitable
world-sheet reparameterizations and dimensional reduction. Cosmological
estimates show that our mechanism generates axion production comparable with
that from the oscillating string loops and may lead to further restrictions on
the axion window.
