Disc accretion onto magnetized compact objects

Abstract

In a slab jet model, the influence of a strong magnetic field and density contrasts on the development of instabilities caused by velocity contrasts is studied in application to disc accretion onto a magnetized compact object. The perturbations propagation transverse to the magnetic field in external regions are shown not to be stable. Strong density contrast at the slab boundary (R = pJpJ cannot stabilize the instability of the acoustic resonance type (ARTI), the fundamental symmetric and antisymmetric modes being still unstable for any finite R. At the same time, a critical value of R exists (R - l/M2, M is the Mach number) at which higher reflection harmonics are stable. We present a comparative analysis of the ARTI and the Kelvin-Helmholtz instability which develops via surface modes at the interfaces between the disc material and magnetic field (magnetosphere). The ARTI can be responsible for the penetration of the accreting material into the magnetosphere.