Gravitational Instability of Perturbations of a Nonlinear Nonstationary Model of a Disklike System. IV. Formation of Double-ring Structures in Galaxies

To find out precise criteria of double-ring structure formation in galaxies, we have studied the problem of gravitational instability of the corresponding structure oscillation modes in the background of a previously described compound disk model [1, 2, 3] with an exact nonlinear law of nonstationarity. Nonstationary analogs have been derived for the dispersion equations for these structure oscillation modes of the model, and the results of their analysis are discussed. A comparative analysis has been carried out for the instability increments of ringlike oscillation modes, aimed at determining the dependence of their characteristic manifestation times on the physical parameters of the model.

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