QPO as the Rosetta Stone for understanding black hole accretion

Quasi periodic oscillations (QPO) seen in the X-ray fluxes of individual neutron stars and black hole sources are one of most intriguing phenomena in today's astrophysics. The QPO nature is visibly determined by super-strong Einstein's gravity. I argue here that it also profoundly depends on the MRI turbulence in accretion flows. Understanding the QPO physics may therefore guide accretion theory out of its present state of confusion.