  We compute the energy density radiated by a quark undergoing circular motion
in strongly coupled $\mathcal N = 4$ supersymmetric Yang-Mills plasma. If it
were in vacuum, this quark would radiate a beam of strongly coupled radiation
whose angular distribution has been characterized and is very similar to that
of synchrotron radiation produced by an electron in circular motion in
electrodynamics. Here, we watch this beam of gluons getting quenched by the
strongly coupled plasma. We find that a beam of gluons of momenta $\sim q \gg
\pi T$ is attenuated rapidly, over a distance $\sim q^{1/3} (\pi T)^{-4/3}$ in
a plasma with temperature $T$. As the beam propagates through the plasma at the
speed of light, it sheds trailing sound waves with momenta $\lesssim \pi T$.
Presumably these sound waves would thermalize in the plasma if they were not
hit soon after their production by the next pulse of gluons from the
lighthouse-like rotating quark. At larger and larger $q$, the trailing sound
wave becomes less and less prominent. The outward going beam of gluon radiation
itself shows no tendency to spread in angle or to shift toward larger
wavelengths, even as it is completely attenuated. In this regard, the behavior
of the beam of gluons that we analyze is reminiscent of the behavior of jets
produced in heavy ion collisions at the LHC that lose a significant fraction of
their energy without appreciable change in their angular distribution or their
momentum distribution as they plow through the strongly coupled quark-gluon
plasma produced in these collisions.
