Astrophysics¶
solid pillar 1
Astrophysical fluid and plasma dynamics, and the numerical methods peculiar to them.
Pages¶
| Page | Covers |
|---|---|
| Radiative transfer | Transfer equation, optical depth, LTE, diffusion and its limits, mean opacities |
| Magnetohydrodynamics | Ideal MHD, flux freezing, plasma beta, the \(\nabla\cdot\mathbf{B}=0\) constraint |
| N-body and gravitational dynamics | Tree and mesh methods, softening, symplectic integration, SPH |
| Plasma physics | Debye length, kinetic vs fluid, PIC and its numerical pathologies |
Code usage for FLASH, Athena, Gadget and ZEUS-MP lives in toolchains › astro codes; these pages cover the physics and the numerics.
What makes astrophysical numerics distinctive¶
Three constraints that rarely bind in engineering CFD and always bind here:
- Enormous dynamic range. Densities and timescales spanning many orders of magnitude in one domain, which is why AMR and individual timesteps are standard rather than exotic.
- Constraints that must hold exactly. \(\nabla\cdot\mathbf{B}=0\) is not a convergence target; violating it produces forces that do not exist.
- Unreachable parameter regimes. Astrophysical \(\mathrm{Rm}\sim10^{10}\) and \(\mathrm{Re}\sim10^{12}\) mean the simulation is never in the physical regime. Numerical resistivity and viscosity always dominate, and the honest question is whether the result depends on them.
Connections¶
- Fluids › Compressible flow — the Riemann machinery MHD extends.
- Foundations › Numerical methods — stability and order.
- Aerospace › Space environment — the near-Earth end of the same physics.
- Toolchains › Astro codes — running these simulations.
Sources¶
Per page. See the course archive for the Astro folders.