Supersonic wind accretion in massive close binary systems: a 3D SPH simulation of Cen X-3

In this paper we study the 3D SPH structure and dynamics of an accretion disc generated in a close binary system by supersonic wind accretion from a massive secondary on to a compact primary. The stellar masses and separation between the two components are characteristic of the Cen X-3 system: the secondary is a 19.1-M⊙ star not filling completely its Roche lobe, while the primary is a white dwarf or a neutron star of 1.4 M⊙. An interesting result of our simulation is that, in a quasi-stationary state attained after ≃ 4 orbital periods, only about three-quarters of the particles released by the secondary penetrate the primary Roche lobe. The disc is remarkably elongated and thick, and consistent deviations from the ‘standard model’ of specific angular momentum and radial temperature distributions have been found. However, the most interesting result is that the azimuthal distribution of the radial Mach number shows oblique structures (spiral shocks), which persist from the outer edge to the inner regions, in contrast to the case of discs formed by the usual LI accretion and even by wind accretion in much less massive systems.