Accretion of plasma by black holes powers all of the most luminous objects in the universe, includingx-ray binaries and active galactic nuclei. In addition, the radiation and outflows produced by accreting black holes produces feedback on their environment, which in turn affects galaxy formation and limits the rate of growth of supermassive black holes in the early universe. It has long been known that the inner regions of luminous accretion flows are dominated by radiation, and therefore modeling these sources requires solving the equations of general relativistic radiation magneto-hydrodynamics (MHD). However, despite the importance of understanding luminous accretion flows for interpreting a variety of astronomical observations, very few calculations of this regime have been performed to date due to the complexity and cost of the methods.

The researchers will survey the properties of accretion flows for both supermassive and stellar mass black holes for a variety of spins, tilt, and accretion rates. They will also study how relativistic jets and outflows produced by combination of magnetic fields and black hole spin are affected by strong radiation fields. To carry out this work, the team will use AthenaK, a new performance-portable version of the Athena++ astrophysical MHD code that usesKokkos.

Their calculations, enabled by emerging exascale architectures, will push the frontier of state-of-the-art modeling of astrophysical accretion flows. The simulations will allow the first direct tests of theoretical models of luminous accretion disks, and moreover, direct comparison to observations will test such important questions as whether spectral fitting methods to measure the mass and spin of black holes are reliable.