  We analyse the formation and evolution of the event horizon of a black hole
binary merger when the black holes are charged. We find that the presence of
charge influences the properties of the merger and can be useful for
investigating the validity of various theories of modified gravity and several
proposals for dark matter candidates. It can moreover give insights into
various aspects of astrophysical phenomena involving black holes, such as
degeneracies in the gravitational wave parameter determination. We perform our
analysis both analytically and numerically, in $D=4$ dimensions, in the Extreme
Mass Ratio (EMR) limit and compare the results. The development of analytical
results in the EMR limit is of uttermost importance in view of the upcoming
observations of the LISA interferometer. We then use our analysis to describe
how the horizon evolves in time during the merger and to investigate the growth
in the area of the event horizon and the duration of the merger. We moreover
provide a numerical solution valid in arbitrary dimensions $D \geq 4$ which
could be of interest in the context of the AdS/CFT correspondence or for
examining possible extensions of general relativity.
