GR-Athena++: Puncture Evolutions on Vertex-centered Oct-tree Adaptive Mesh Refinement

Numerical relativity is central to the investigation of astrophysical sources in dynamical and strong-field gravity regime, such as binary black hole neutron star coalescences. Current challenges set by gravitational-wave multi-messenger astronomy call for highly performant scalable codes on modern massively-parallel architectures. We present GR-Athena++, a general-relativistic, high-order, vertex-centered solver that extends oct-tree, adaptive mesh refinement capabilities (radiation) magnetohydrodynamics code Athena++. To simulate space-times GR-Athena++ uses Z4c evolution scheme numerical coupled moving puncture gauge. demonstrate stable accurate merger evolutions via extensive convergence testing, cross-code validation, verification against state-of-the-art effective-one-body waveforms. leverages task-based parallelism paradigm Athena++ achieve excellent scalability. measure strong scaling efficiencies above $95\%$ up $\sim 1.2\times10^4$ CPUs weak shown 10^5$ production setup with refinement. thus allows robust simulation compact coalescences offers viable path towards at exascale.