Relativistic Hydro Research Articles

Xtroem-fv: a new code for computational astrophysics based on very high order finite-volume methods – II. Relativistic hydro- and magnetohydrodynamics

xtroem-fv: a new code for computational astrophysics based on very high order finite-volume methods – II. Relativistic hydro- and magnetohydrodynamics

Relativistic HD and MHD modelling for AGN jets

Relativistic hydro and magnetohydrodynamics (MHD) provide a continuum fluid description for plasma dynamics characterized by shock-dominated flows approaching the speed of light. Significant progress in its numerical modelling emerged in the last two decades; we highlight selected examples of modern grid-adaptive, massively parallel simulations realized by our open-source software MPI-AMRVAC (Keppens et al 2012 J. Comput. Phys. 231 718). Hydrodynamical models quantify how energy transfer from active galactic nuclei (AGN) jets to their surrounding interstellar/intergalactic medium (ISM/IGM) gets mediated through shocks and various fluid instability mechanisms (Monceau-Baroux et al 2012 Astron. Astrophys. 545 A62). With jet parameters representative for Fanaroff–Riley type-II jets with finite opening angles, we can quantify the ISM volumes affected by jet injection and distinguish the roles of mixing versus shock-heating in cocoon regions. This provides insight in energy feedback by AGN jets, usually incorporated parametrically in cosmological evolution scenarios. We discuss recent axisymmetric studies up to full 3D simulations for precessing relativistic jets, where synthetic radio maps can confront observations. While relativistic hydrodynamic models allow one to better constrain dynamical parameters like the Lorentz factor and density contrast between jets and their surroundings, the role of magnetic fields in AGN jet dynamics and propagation characteristics needs full relativistic MHD treatments. Then, we can demonstrate the collimating properties of an overal helical magnetic field backbone and study differences between poloidal versus toroidal field dominated scenarios (Keppens et al 2008 Astron. Astrophys. 486 663). Full 3D simulations allow one to consider the fate of non-axisymmetric perturbations on relativistic jet propagation from rotating magnetospheres (Porth 2013 Mon. Not. R. Astron. Soc. 429 2482). Self-stabilization mechanisms related to the detailed magnetic pitch variations are discussed.

Topical issue on relativistic hydro- and thermodynamics

Topical issue on relativistic hydro- and thermodynamics

The effect of angular opening on the dynamics of relativistic hydro jets

Context. Relativistic jets emerging from AGN cores transfer energy from the core to their surrounding ISM/IGM. Because jets are observed to have finite opening angles, one needs to quantify the role of conical versus cylindrical jet propagation in this energy transfer. Aims. We use FR-II AGN jets parameter with finite opening angles. We study the effect of the variation of the opening angle on the dynamics and energy transfer of the jet. We also point out how the characteristics of this external medium, such as its density profile, play a role in the dynamics. Methods. This study exploits our parallel AMR code MPI-AMRVAC with its special relativistic hydrodynamic model, incorporating an equation of state with varying effective polytropic index. We studied mildly under-dense jets up to opening angles of 10 degrees, at Lorentz factors of about 10, inspired by observations. Instantaneous quantification of the various ISM volumes and their energy content allows one to quantify the role of mixing versus shock-heated cocoon regions over the time intervals. Results. We show that a wider opening angle jet results in a faster deceleration of the jet and leads to a wider cocoon dominated by Kelvin-Helmholtz and Rayleigh-Taylor instabilities. The energy transfer mainly occurs in the shocked ISM region by both the frontal bow shock and cocoon-traversing shock waves, in a roughly 3 to 1 ratio to the energy transfer of the mixing zone, for a 5 degree opening angle jet. A rarefaction wave induces a dynamically formed layered structure of the jet beam. Conclusions. Finite opening angle jets can efficiently transfer significant fractions (25 % up to 70 %) of their injected energy over a growing region of shocked ISM matter. The role of the ISM stratification is prominent for determining the overall volume that is affected by relativistic jet injection.

Parallel, grid-adaptive approaches for relativistic hydro and magnetohydrodynamics

Relativistic hydro and magnetohydrodynamics provide continuum fluid descriptions for gas and plasma dynamics throughout the visible universe. We present an overview of state-of-the-art modeling in special relativistic regimes, targeting strong shock-dominated flows with speeds approaching the speed of light. Significant progress in its numerical modeling emerged in the last two decades, and we highlight specifically the need for grid-adaptive, shock-capturing treatments found in several contemporary codes in active use and development. Our discussion highlights one such code, MPI-AMRVAC (Message-Passing Interface-Adaptive Mesh Refinement Versatile Advection Code), but includes generic strategies for allowing massively parallel, block-tree adaptive simulations in any dimensionality. We provide implementation details reflecting the underlying data structures as used in MPI-AMRVAC. Parallelization strategies and scaling efficiencies are discussed for representative applications, along with guidelines for data formats suitable for parallel I/O. Refinement strategies available in MPI-AMRVAC are presented, which cover error estimators in use in many modern AMR frameworks. A test suite for relativistic hydro and magnetohydrodynamics is provided, chosen to cover all aspects encountered in high-resolution, shock-governed astrophysical applications. This test suite provides ample examples highlighting the advantages of AMR in relativistic flow problems.

Shock refraction from classical gas to relativistic plasma environments

AbstractThe interaction of (strong) shock waves with localized density changes is of particular relevance to laboratory as well as astrophysical research. Shock tubes have been intensively studied in the lab for decades and much has been learned about shocks impinging on sudden density contrasts. In astrophysics, modern observations vividly demonstrate how (even relativistic) winds or jets show complex refraction patterns as they encounter denser interstellar material.In this contribution, we highlight recent insights into shock refraction patterns, starting from classical up to relativistic hydro and extended to magnetohydrodynamic scenarios. Combining analytical predictions for shock refraction patterns exploiting Riemann solver methodologies, we confront numerical, analytical and (historic) laboratory insights. Using parallel, grid-adaptive simulations, we demonstrate the fate of Richtmyer-Meshkov instabilities when going from gaseous to magnetized plasma scenarios. The simulations invoke idealized configurations closely resembling lab analogues, while extending them to relativistic flow regimes.

GENESIS: A High‐Resolution Code for Three‐dimensional Relativistic Hydrodynamics

The main features of a three-dimensional, high-resolution special relativistic hydro code based on relativistic Riemann solvers are described. The capabilities and performance of the code are discussed. In particular, we present the results of extensive test calculations that demonstrate that the code can accurately and efficiently handle strong shocks in three spatial dimensions. Results of the performance of the code on single and multiprocessor machines are given. Simulations (in double precision) with ≤7×106 computational cells require less than 1 Gbyte of RAM memory and ≈ 7×10-5 CPU s per zone and time step (on a SCI Cray-Origin 2000 with a R10000 processor). Currently, a version of the numerical code is under development, which is suited for massively parallel computers with distributed memory architecture (such as, e.g., Cray T3E).

Numerical simulation of thick disc accretion on to a rotating black hole

We study two-dimensional axisymmetric accretion on to a rotating black hole by time-dependent fully relativistic hydro dynamical calculations. We investigate the innermost part of geometrically thick discs, in which most of the gravitationally released energy is advected into the black hole. Relativistic effects are important close to the cusp-like inner edge of the disc, where accretion proceeds with approximately constant angular momentum and the viscous time-scale exceeds the dynamical time-scale of accretion. We use the perfect fluid approximation and calculate isentropic flows with constant angular momentum. We confirm the previous analytical result that the structure of the innermost disc region strongly depends on the black hole spin. We find the mass accretion rate M to be in a good agreement with the analytical dependenceM oc (dW)rJ(r-I), where dWis the energy gap and r is the adiabatic index.

Relativistic hydro- and thermodynamics in nonlinear scalar field

A classical relativistic theory is proposed describing the hydrodynamics and thermodynamics of fermions in the presence of a nonlinear scalar field, which contributes to the rest mass of particles. The macro and microdynamics (i.e. hydrodynamics and Fermi motion) are separated in a covariant way. The obtained equations of motion, of field and of state are consistent with thermodynamics and with the conventional formulation of relativistic hydrodynamics. Static solutions can describe e.g. cosmological domain walls or scalar bags. The acoustic and scalar waves propagating in the medium have been investigated.

Relativistic hydrodynamics with irreversible thermodynamics without the paradox of infinite velocity of heat conduction

This paper presents the special relativistic hydro thermodynamics (i. e.) dynamics of mechanico-thermal processes) in covariant form for a simple viscous fluid, free of the paradox of infinite velocity of heat conduction. The theory was developed by correcting Eckart’s theory (1) admitting also infinitely fast heat propagation which is incompatible with Einstein’s principle of relativity. The paradox was eliminated in part by replacing the relation between heat flow and temperature — the so-called Fourier’s phenomenological transport equation — by a more exact equation due toCattaneo andVernotte (2,3), and in part by changing in a corresponding manner the energy-momentum tensor. The new energy-momentum tensor contains all terms appearing in Eckart’s tensor, as well as terms having in coefficient factors 1/V2 whereV is the greatest heat velocity in the medium. Finally it is shown that also for diffusion processes one can eliminate the paradox of instantaneous propagation of diffusion flux from the equations describing relativistic diffusion phenomena.