  It is well known that massive black holes may form through the gravitational
collapse of a massive astrophysical body. Less known is the fact that a black
hole can be produced by the quantum process of pair creation in external
fields. These black holes may have a mass much lower than their astrophysical
counterparts. This mass can be of the order of Planck mass so that quantum
effects may be important. This pair creation process can be investigated
semiclassically using non-perturbative instanton methods, thus it may be used
as a theoretical laboratory to obtain clues for a quantum gravity theory. In
this work, we review briefly the history of pair creation of particles and
black holes in external fields. In order to present some features of the
euclidean instanton method which is used to calculate pair creation rates, we
study a simple model of a scalar field and propose an effective one-loop action
for a two-dimensional soliton pair creation problem. This action is built from
the soliton field itself and the soliton charge is no longer treated as a
topological charge but as a Noether charge. The results are also valid
straightforwardly to the problem of pair creation rate of domain walls in
dimensions greater than 2.
