  Binary black holes (BBHs) appear to be widespread and are able to merge
through the emission of gravitational waves, as recently illustrated by LIGO.
The spin of the BBHs is one of the parameters that LIGO can infer from the
gravitational wave signal and can be used to constrain their production site.
If BBHs are assembled in stellar clusters they are likely to interact with
stars, which could occasionally lead to a tidal disruption event (TDE). When a
BBH tidally disrupts a star it can accrete a significant fraction of the
debris, effectively altering the spins of the BHs. Therefore, although
dynamically formed BBHs are expected to have random spin orientations, tidal
stellar interactions can significantly alter their birth spins both in
direction and magnitude. Here we investigate how TDEs by BBHs can affect the
properties of the BH members as well as exploring the characteristics of the
resulting electromagnetic signatures. We conduct hydrodynamic simulations with
a Lagrangian Smoothed Particle Hydrodynamics code of a wide range of
representative tidal interactions. We find that both spin magnitude and
orientation can be altered and temporarily aligned or anti-aligned through
accretion of stellar debris, with a significant dependence on the mass ratio of
the disrupted star and the BBH members. These tidal interactions feed material
to the BBH at very high accretion rates, with the potential to launch a
relativistic jet. The corresponding beamed emission is a beacon to an otherwise
quiescent BBH.
