Octo-Tiger: A new, 3D hydrodynamic code for stellar mergers that uses HPX parallelization

octo-tiger is an astrophysics code to simulate the evolution of self-gravitating and rotating systems of arbitrary geometry based on the fast multipole method, using adaptive mesh refinement. octo-tiger is currently optimized to simulate the merger of well-resolved stars that can be approximated by barotropic structures, such as white dwarfs (WDs) or main-sequence stars. The gravity solver conserves angular momentum to machine precision, thanks to a 'correction' algorithm. This code uses hpx parallelization, allowing the overlap of work and communication and leading to excellent scaling properties, allowing for the computation of large problems in reasonable wall-clock times. In this paper, we investigate the code performance and precision by running benchmarking tests. These include simple problems, such as the Sod shock tube, as well as sophisticated, full, WD binary simulations. Results are compared to analytical solutions, when known, and to other grid-based codes such as flash. We also compute the interaction between two WDs from the early mass transfer through to the merger and compare with past simulations of similar systems. We measure octo-tiger's scaling properties up to a core count of ∼80 000, showing excellent performance for large problems. Finally, we outline the current and planned areas of development aimed at tackling a number of physical phenomena connected to observations of transients.