  Black hole superradiance has proven being very valuable in several realms of
gravitational physics, and holds a promising discovery potential. In this
paper, we show how it can sheed light on a long standing problem in physics,
the quest for magnetic monopoles in the Universe. Placing them in the interior
of primordial rotating black holes, which act as natural amplifiers, we show
that massive charged bosonic fields in their vicinity exhibit a superradiant
instability which surpasses significantly that of neutral Kerr black holes.
Strikingly, this is true for black holes containing an order-one number of
magnetic monopoles, or merely a single one, and possessing either low, moderate
or large values of angular momentum. In particular, the instability is
drastically faster than the radiative decay time of charged pions, thus making
it physically relevant. Furthermore, our analysis identifies the most unstable
modes as a class of monopole spheroidal harmonics, that we dub north and south
monopole modes, whose morphology is markedly different from the usual
superradiantly unstable modes since they extend along the rotational axis. We
conclude by discussing implications of our results for primordial magnetic
black holes, and their observational signatures as sources of cosmic rays and
high-frequency gravitational waves.
