Abstract
When astrophysical jets were discovered one hundred years ago, the field of numerical simulations did not yet exit. Since the arrival of programmable computers though, numerical simulations have increasingly become an indispensable tool for dealing with “tough nut” problems which involve complex dynamic and non-linear phenomena. Astrophysical jets are an ideal example of such a tough nut, where multi-scale plasma physics, radiative and non-thermal processes, turbulence and relativity combine to present a formidable challenge to researchers.Highlighting major achievements obtained through numerical simulations concerning the validity and nature of the Blandford–Znajek mechanism, the launching, collimation, acceleration and stability of jets, their interaction with the surrounding plasma, jet-galaxy feedback mechanisms etc., we trace how the field developed from its first tentative steps into the age of “maturity”. We also give a brief and personal outlook on how the field may evolve in the foreseeable future.
Highlights
In the jet simulations by Rayburn (1977) and Norman et al (1982), as well as in the numerous other studies that followed, the jets were injected into the computational domain as cylindrical flows with velocities perfectly aligned to the symmetry axis
The results demonstrated that for the degree of magnetization which can be achieved in GRMHD schemes with reasonably high resolution, (1) the electromagnetic part of the MHD solution stays quite close to the BZ solution; (2) within the ergosphere the plasma is not pushed into orbits with high Lorentz factor and its inertia remains small, in contrast to what is envisioned in the MHD-Penrose process; (3) the in situ injection of matter can be done in the way that does not corrupt the electromagnetic solution
If flux can be effectively transported from larger radii, the magnetic field strength increases due to the decreasing surface area and its accumulating pressure will halt the accretion process, forming a magnetically-arrested-disk’’ regime (MAD) (Bisnovatyi-Kogan and Ruzmaikin, 1976; Narayan et al, 2003)
Summary
Twenty five years after the discovery of the M87 jet by Curtis (1918), the efforts of the British to break encrypted communications of the Germans during the WW2 were facilitated by the arrival of the first ever electronic programmable computer Colossus (Copeland, 2006). For the numerical solution to be reasonably accurate the number of grid points has to be large and so is the amount of calculations needed to populate them with the values of dependent variables This is why before the arrival of powerful computers, the numerical approach was practical only for a rather limited number of mathematical problems. Provided the theoretical framework (the set of evolution equations) is adequate, the numerical method is efficient and the computational power is sufficient, the outcome can be very close to reality in many respects This approach is valuable where real experiments are practically impossible, which includes the whole of Astrophysics
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