  The origin of fast radio bursts (FRBs) remains mysterious. Recently, the only
repeating FRB source, FRB 121102, was reported to possess an extremely large
and variable rotation measure (RM). The inferred magnetic field strength in the
burst environment is comparable to that in the vicinity of the super-massive
black hole Sagittarius A* of our Galaxy. Here we show that all the
observational properties of FRB 121102 (including the high RM and its
evolution, the high linear polarization degree, an invariant polarization angle
across each burst and other properties previously known) can be interpreted
within the cosmic comb model invoking a regular neutron star whose
magnetosphere is sporadically and marginally combed by a variable outflow from
a nearby low-luminosity accreting super-massive black hole in the host galaxy.
We propose three falsifiable predictions of the model and discuss other FRBs
within the context of the cosmic comb model as well as the challenges
encountered by other repeating FRB models in light of the new observations.
