A new method for extending solutions to the self-similar relativistic magnetohydrodynamic equations for black hole outflows

• Published in: Monthly notices of the Royal Astronomical Society 2018-02, Vol.473 (4), p.4417-4435
• Main Authors: Ceccobello, C., Cavecchi, Y., Heemskerk, M. H. M., Markoff, S., Polko, P., Meier, D.
• Format: Article
• Language: English
• Subjects: Astronomical models; Black holes; Collimation; Computational fluid dynamics; Fluid flow; Magnetic fields; Magnetohydrodynamic equations; Magnetohydrodynamics; Morphology; Nonlinear equations; Relativism; Relativistic effects; Self-similarity; Singularities; Thermal energy
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stx2567

Abstract The paradigm in which magnetic fields play a crucial role in launching/collimating outflows in many astrophysical objects continues to gain support. However, semi-analytical models including the effect of magnetic fields on the dynamics and morphology of jets are still missing due to the intrinsic difficulties in integrating the equations describing a collimated, relativistic flow in the presence of gravity. Only few solutions have been found so far, due to the highly non-linear character of the equations together with the need to blindly search for singularities. These numerical problems prevented a full exploration of the parameter space. We present a new integration scheme to solve r-self-similar, stationary, axisymmetric magnetohydrodynamic (MHD) equations describing collimated, relativistic outflows crossing smoothly all the singular points (Alfvén point and modified slow/fast points). For the first time, we are able to integrate from the disc mid-plane to downstream of the modified fast point. We discuss an ensemble of jet solutions, emphasizing trends and features that can be compared to observables. We present, for the first time with a semi-analytical MHD model, solutions showing counter-rotation of the jet for a substantial fraction of its extent. We find diverse jet configurations with bulk Lorentz factors up to 10 and potential sites for recollimation between 103 and 107 gravitational radii. Such extended coverage of the intervals of quantities, such as magnetic-to-thermal energy ratios at the base or the heights/widths of the recollimation region, makes our solutions suitable for application to many different systems where jets are launched.