Octo-Tiger: A New, 3D Hydrodynamic Code for Stellar Mergers that uses HPX Parallelisation

TL;DR

OCTO-TIGER is a high-performance 3D hydrodynamic code utilizing HPX parallelization to simulate stellar mergers with high accuracy and scalability, enabling detailed astrophysical studies of white dwarf interactions.

Contribution

The paper introduces OCTO-TIGER, a novel astrophysics simulation code that combines adaptive mesh refinement, a conserved gravity solver, and HPX parallelization for scalable stellar merger modeling.

Findings

Excellent scaling up to 80,000 cores.

Accurate simulation of white dwarf mergers.

Good agreement with analytic solutions and other codes.

Abstract

OCTO-TIGER is an astrophysics code to simulate the evolution of self-gravitating and rotat-ing systems of arbitrary geometry based on the fast multipole method, using adaptive mesh refinement. OCTO-TIGER is currently optimised to simulate the merger of well-resolved stars that can be approximated by barotropic structures, such as white dwarfs 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, white-dwarf binary simulations. Results are compared to analytic solutions, when known, and to other grid based codes such as FLASH. We also compute the interaction between two white dwarfs from the early mass transfer through to the merger and compare with past simulations of similar systems. We measure OCTO-TIGERs 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.