  At high energy densities any quantum field theory is expected to have an
effective hydrodynamic description. When combined with the gravity/gauge
duality an unified picture emerges, where gravity itself can have a formal
holographic hydrodynamic description. This provides a powerful tool to study
black holes in a hydrodynamic setup. We study the stability of plasma balls,
holographic duals of Scherck-Schwarz (SS) AdS black holes. We find that
rotating plasma balls are unstable against m-lobed perturbations for rotation
rates higher than a critical value. This unstable mode signals a bifurcation to
a new branch of non-axisymmetric stationary solutions which resemble a
"peanut-like" rotating plasma. The gravitational dual of the rotating plasma
ball must then be unstable and possibly decay to a non-axisymmetric long-lived
SS AdS black hole. This instability provides therefore a mechanism that bounds
the rotation of SS black holes. Our results are strictly valid for the SS AdS
gravity theory dual to a SS gauge theory. The latter is particularly important
because it shares common features with QCD, namely it is non-conformal,
non-supersymmetric and has a confinement/deconfinement phase transition. We
focus our analysis in 3-dimensional plasmas dual to SS AdS_5 black holes, but
many of our results should extend to higher dimensions and to other gauge
theory/gravity dualities with confined/deconfined phases and admitting a fluid
description.
