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Origin of wide varieties of quasi-periodic oscillation (QPO) observed incompact sources is still not well established. Its frequencies range from mHzto kHz spanning all compact objects. Are different QPOs, with differentfrequencies, originating from different Physics? We propose that the emergenceof QPOs is the result of nonlinear resonance of fundamental modes present inaccretion disks forced by external modes including that of the spin of theunderlying compact object. Depending on the properties of accreting flow, e.g.its velocity and gradient, resonances, and any mode locking, take place atdifferent frequencies, exhibiting low to high frequency QPOs. We explicitlydemonstrate the origin of higher frequency QPOs for black holes and neutronstars by a unified model and outline how the same physics could be responsibleto produce lower frequency QPOs. The model also predicts the spin of blackholes, and constrains the radius of neutron stars and the mass of both.

QPOs in compact sources as a non-linear hydrodynamical resonance: Determining spin of compact objects