3 mins read 14 May 2021

New Astrophysics Code Rapidly Models Stellar Collisions

A new astrophysics code from a collaboration involving Macquarie University can rapidly and more efficiently model stellar collisions.

A new code called “Octo-Tiger” is helping to break the barrier between computer science and astrophysics. The code is used to more efficiently model stellar collisions, simulating the evolution of self-gravitating and rotating systems using adaptive mesh refinement and a new method to parallelise the code to be faster than its predecessors. 

Professor Orsola De Marco from Macquarie University's Department of Physics and Astronomy was part of a collaboration between experimental computer scientists and astrophysicists in the LSU Department of Physics & Astronomy, the LSU Center for Computation & Technology, Indiana University Kokomo, and Macquarie University to develop Octo-Tiger. Professor De Marco commented on the impressive results of the code. 

“A test on Australia’s fastest supercomputer, Gadi (number 25 in the World’s Top 500 list), showed that Octo-Tiger, running on a core count over 80,000, displays excellent performance for large models of merging stars,” Professor De Marco said. “With Octo-Tiger, we cannot only reduce the wait time dramatically, but our models can answer many more of the questions we care to ask.”

The development of Octo-Tiger culminated in over a year of testing and simulations outlined in a research paper, supported by multiple National Science Foundation grants, including one specifically designed to break the barrier between computer science and astrophysics.

Testing Octo-Tiger

An Octo-tiger simulation of two stars as they start to merge together. Credit: Dr. Sagiv Shiber.

A recently published paper from this collaboration in the Monthly Notices of the Royal Astronomical Society outlines benchmark testing completed to test Octo-Tiger’s performance. The results of the code were compared with prior-known solutions where possible, and other grid-based codes such as FLASH. They also modelled the interaction between two white dwarfs and their merging (see the video at the top of this page), and compared these results with similar past simulations.

“This paper demonstrates how an asynchronous task-based runtime system can be used as a practical alternative to Message Passing Interface to support an important astrophysical problem,” Dr Patrick Diehl, one of the authors of the paper, said.

Dr Patrick Motl from Indiana University Kokomo, another author of the paper, commented on the potential of Octo-Tiger in astrophysics research. 

“Thanks to a significant effort across this collaboration, we now have a reliable computational framework to simulate stellar mergers,” said Dr Motl. “By substantially reducing the computational time to complete a simulation, we can begin to ask new questions that could not be addressed when a single-merger simulation was precious and very time consuming. We can explore more parameter space, examine a simulation at very high spatial resolution or for longer times after a merger, and we can extend the simulations to include more complete physical models by incorporating radiative transfer, for example.”

Octo-Tiger is currently optimised to simulate the merger of well-resolved stars, such as white dwarf or main sequence stars. The code’s use of HPX (High Performance ParalleX) parallelisation to solve larger problems in shorter time frames shows potential for broader use in astrophysics.

“While our particular research interest is in stellar mergers and their aftermath, there are a variety of problems in computational astrophysics that Octo-Tiger can address with its basic infrastructure for self-gravitating fluids,” said Dr Motl. 

Video Credit: Dr. Sagiv Shiber.

Read the full paper now, available from the Monthly Notices of the Royal Astronomical Society.