Radiative Transfer in Fast-moving Media: The Limit of the Diffusion Approximation
Abstract
The diffusion approximation is a powerful tool to treat radiative transfer in optically thick media. Here, a fundamental limit is shown for the applicability of this approximation when it is used in high-velocity regions; e.g., in accretion columns on neutron stars. The reason for this limitation is the strong advection effect, which strongly impedes the photon transport against the flow of the matter. The essential assumption for the validity of the diffusion equation (namely, that the anisotropy does not become too large) is violated.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1989
- DOI:
- 10.1086/185524
- Bibcode:
- 1989ApJ...344L..33R
- Keywords:
-
- Diffusion Theory;
- Radiative Transfer;
- Stellar Mass Accretion;
- Approximation;
- Neutron Stars;
- Optical Thickness;
- Astrophysics;
- ACCRETION;
- DIFFUSION;
- RADIATIVE TRANSFER