  Ultrarelativistic heavy ion collisions produce a quark-gluon matter which
lies in the future light cone originating from given points on the $t=z=0$
plane of the Minkowski spacetime manifold. We show that in a weak coupling
regime the Minkowski vacuum of massless fields presents itself in the "Little
Bang" region as a thermal state of low $p_{T}$ particles, in close analogy to
the Unruh effect for uniformly accelerated observers which are causally
restricted to a Rindler wedge. It can shed some light on the mechanisms of
early time thermalization in ultrarelativistic heavy ion collisions.
