Epicyclic Oscillations of Fluid Bodies: Newtonian Nonslender Torus

Understand

We study epicyclic oscillations of fluid tori around black holes (in the Paczynski-Wiita potential) and derive exact analytic expressions for their radial and vertical eigenfrequencies nu_r and nu_z to second-order accuracy in the width of the torus.

• We prove that pressure effects make the eigenfrequencies smaller than those for free particles.
• However, the particular ratio nu_z/nu_r=3/2, which is important for the theory of high-frequency quasi-periodic oscillations (QPOs), occurs when the fluid tori epicyclic frequencies nu_r and nu_z are about 15% higher than the ones corresponding to free particles.
• Our results therefore suggest that previous estimates of black hole spins from QPOs have produced values that are too high.