Publication date: Jan 2021
Abstract:
Investigation of a fluid circulation in strong gravitational fields represents a fundamental method for theoretical exploration of accretion discs and related processes. The fluid is commonly considered as a neutral gas, or as a quasi-neutral and highly conductive plasma, which can form a toroidal-like structure centered and circling along equatorial plane of a central object. Such a scenario stands for a basic model of thick accretion disc around a black hole or compact star, where the accretion can occur close to an equatorial cusp. Here, we show that if the circling fluid is electrically charged so that it possesses a net non-zero charge transported only by convection, it can form unique structures supposed that a proper ambient large-scale electromagnetic field is present around; along with the pure equatorial toroidal structures with equatorial cusps, characteristic for a neutral fluid circulation, we also find unique off-equatorial toroidal structures with off-equatorial cusps, the so-called `levitating tori‘, or circling structures with polar cusps hovering above a central object, referred to as `polar clouds‘, etc. These structures, constructed within the presented general relativistic magneto-hydrodynamic model, demonstrate the importance of consideration of a fluid charge for investigation of accretion processes. Even small net charge of the circling fluid together with a sufficiently strong ambient electromagnetic field can distinctively affect the commonly studied equatorial accretion scenario — shifting it up to the polar region.
Authors:
Kovar, Jiri; Stuchlik, Zdenek; Karas, Vladimir; Slany, Petr; Trova, Audrey;