  It has been proved in the context of quantum fields in Minkowski spacetime
that the vacuum state is a thermal state according to uniformly accelerated
observers -- a seminal result known as the Unruh effect. Recent claims,
however, have challenged the validity of this result for extended systems, thus
casting doubts on its physical reality. Here, we study the dynamics of an
extended system, uniformly accelerated in the vacuum. We show that its reduced
density matrix evolves to a Gibbs thermal state with local temperature given by
the Unruh temperature. This proves that the vacuum state does induce
thermalization of an accelerated extended system -- which is all one can expect
of a legitimate thermal reservoir.
