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Hardly any of the observed black hole accretion disks in X-Ray binaries andactive galaxies shows constant flux. When the local stochastic variations ofthe disk occur at specific regions where a resonant behaviour takes place,there appear the Quasi-Periodic Oscillations (QPOs). If the global structure ofthe flow and its non-linear hydrodynamics affects the fluctuations, thevariability is chaotic in the sense of deterministic chaos. Our aim is to solvea problem of the stochastic versus deterministic nature of the black holebinaries vari- ability. We use both observational and analytic methods. We usethe recurrence analysis and we study the occurence of long diagonal lines inthe recurrence plot of observed data series and compare it to the sur- rogateseries. We analyze here the data of two X-Ray binaries - XTE J1550-564, and GX339-4 observed by Rossi X-ray Timing Explorer. In these sources, the non-linearvariability is expected because of the global conditions (such as the meanaccretion rate) leading to the pos- sible instability of an accretion disk. Thethermal-viscous instability and fluctuations around the fixed-point solutionoccurs at high accretion rate, when the radiation pressure gives dominantcontribution to the stress tensor.

Deterministic chaos in the X-Ray sources