Should One Use the Ray-by-Ray Approximation in Core-collapse Supernova Simulations?

Abstract

We perform the first self-consistent, time-dependent, multi-group calculations in two dimensions(2D)to address the consequences of using the ray-by-ray+transport simplification in core-collapse supernova simulations. Such a dimensional reduction is employed by many researchers to facilitate their resource-intensive calculations. Our newcode (FORNAX) implements multi-D transport, and can, by zeroing out transverse flux terms, emulate the ray-by-ray+scheme. Using the same microphysics, initial models, resolution, and code, we compare the results of simulating 12, 15, 20, and 25Meprogenitor models using these two transport methods. Our findings call into question the wisdom of the pervasive use of the ray-by-ray+approach. Employing it leads to maximum post-bounce/pre-explosion shock radii that are almost universally larger by tens of kilometers than those derived using the more accurate scheme, typically leaving the post-bounce matter less bound and artificially more “explodable.” In fact, for our 25Meprogenitor, the ray-by-ray+model explodes, while the corresponding multi-D transport model does not. Therefore, in two dimensions, the combination of ray-by-ray+with the axial sloshing hydrodynamics that is a feature of 2D supernova dynamics can result in quantitatively, and perhaps qualitatively,incorrect results.