I will present cuHARM, a general relativistic radiation magnetohydrodynamic solver optimized to exploit exascale computing facilities. After describing the core numerical strategies enabling efficient calculation for multi-node and multi-GPU architectures, I will discuss how radiative cooling changes the dynamics of magnetically arrested accretion disks.
In the second part of the talk, I will detail how radiation and its feedback on the dynamics are modeled. In cuHARM, the specific intensity is discretized in space and momentum, and is evolved through the solution of the radiative transfer equation via the discrete ordinate method. This approach eliminates the need for a closure relation and enables to resolve the anisotropy of the specific intensity. Finally, I will present the first results obtained for a radiative accretion disk operating at 0.1 times the Eddington luminosity.