  It is generally assumed that ionization in slow collisions of light atomic
particles, whose constituents (electrons and nuclei) move with velocities
orders of magnitude smaller than the speed of light, is driven solely by the
Coulomb force. Here we show, however, that the Breit interaction -- a
relativistic correction to the Coulomb interaction between electrons -- can
become the main actor when the colliding system couples resonantly to the
quantum radiation field. Our results demonstrate that this ionization mechanism
can be very efficient in various not too dense physical environments, including
stellar plasmas and atomic beams propagating in gases.
