http://arxiv.org/abs/1708.08452
General relativistic radiation hydrodynamics simulations are necessary to accurately model a number of astrophysical systems involving black holes and neutron stars. Photon transport plays a crucial role in radiatively dominated accretion disks, while neutrino transport is critical to core-collapse supernovae and to the modeling of electromagnetic transients and nucleosynthesis in neutron star mergers. However, evolving the full Boltzmann equations of radiative transport is extremely expensive. We describe the implementation of a cheaper general relativistic radiation hydrodynamics method which explicitly converges to a solution of Boltzmann’s equation in the limit of infinite numerical resources. The algorithm is based on a gray two-moment scheme, in which we evolve the energy density and momentum density of the radiation. Two-moment schemes require a closure which fills in missing information about the energy spectrum and higher-order moments of the radiation. Instead of the approximate analytical closure currently used in core-collapse and merger simulations, we complement the two-moment scheme with a low-accuracy Monte-Carlo evolution. We describe how the two algorithms are coupled for self-consistent evolutions, and present a set of test problems demonstrating the reliability of our implementation of that algorithm in the general relativistic SpEC code, and its current limitations. We expect these methods to allow for greatly improved accuracy in the evolution of neutrinos in neutron star merger simulations. Our algorithm can also be useful in radiation hydrodynamics simulations of other general relativistic systems.
F. Foucart
Wed, 30 Aug 2017
50/67
Comments: 17p, 12 figs, submitted to MNRAS
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