Abstract
We study the stability of accretion disc around magnetised stars. Starting from the equations of magnetohydrodynamics we derive equations for linearized perturbation of geometrically thin, optically thick axisymmetric accretion disc with an internal dynamo around magnetized stars. The structure and evolution of such discs are governed by an evolution equation for matter surface density ∑(R,T). Using the time-dependent equations for an accretion disc we do a linear stability analysis of our steady disc solutions in the presence of the magnetic field generated due to an internal dynamo.
Highlights
After the establishment of the standard thin accretion disc model by [1], its stability has become an important area in the accretion disc theory
Since instabilities of accretion discs permit to explain the observed phenomena of variability and luminosity of various astronomical objects, such as X-ray binaries, black holes, active galactic nuclei, etc., many authors have carried out studies on the instabilities of accretion discs using standard model. [2] found that in the innermost regions of accretion discs around stellar mass neutron stars or black holes, where electron scattering is the dominant source of opacity and radiation pressure is much greater than gas pressure, the disk flow would be viscously unstable if radiation pressure was to determine the magnitude of viscosity in the α ~ prescription
Our approach is an extension of the standard model for a thin accretion disc [1], and it follows closely the method that we introduced in Paper I & II, though we will consider general time-dependent equations around magnetised stars
Summary
After the establishment of the standard thin accretion disc model by [1], its stability has become an important area in the accretion disc theory. [5] undertook a more general stability analysis by considering the evolution of infinitesimal perturbations of all three components of the fluid velocity as well as temperature, T and surface density Σ , and he found that the disc exhibited pulsational instability besides the viscous and thermal instability. [10] hereafter Paper I, have investigated the interaction between magnetic neutron star and its surrounding accretion disc in the case where the accretion disc is supporting an internal dynamo. The purpose of the present work is to study the time dependent behavior of thin, axisymmetric accretion disc with an internal dynamo around magnetised stars. This will be used to determine the stability properties of our disc model which has been developed in Paper I & II.
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