Our Octo-Tiger team here in the STE||AR Group are making waves with their newly published journal article in Monthly Notices of the Royal Astronomical Society, “Octo-Tiger: A New, 3D Hydrodynamic Code for Stellar Mergers That Uses HPX Parallelisation,”
The paper investigates the code performance and precision through benchmark testing. The authors, Dominic C. Marcello, postdoctoral researcher; Sagiv Shiber, postdoctoral researcher; Juhan Frank, professor; Geoffrey C. Clayton, professor; Patrick Diehl, research scientist; and Hartmut Kaiser, research scientist, all at LSU — together with collaborators Orsola De Marco, professor at Macquarie University and Patrick M. Motl, professor at Indiana University Kokomo — compared their results to analytic solutions, when known and other grid-based codes, such as the popular FLASH. In addition, they computed the interaction between two white dwarfs from the early mass transfer through to the merger and compared the results with past simulations of similar systems.
The LSU Physics and Astronomy press release was picked up by almost a dozen computer science and other media sites, including Phys.org, and SciTechDaily. This is an exciting breakthrough as the astrophysics code outlined in the article is able to quickly and accurately simulate the collision of stars.
Understanding stars is fundamental to understanding the smaller planets that orbit them and the large galaxies they inhabit. Stars change over million to billion-year timescales in complex ways, particularly if we consider that many of them are orbited by one or more close companions, with which they exchange mass at different stages during their lives. Recent observations of these mass exchanges as flashes of light, or “transients”, show us a fundamentally new paradigm of stellar evolution, where even well-known phenomena like supernovae need to be understood in a new light. We need to include interacting, multiple stars in our models to explain exploding, outbursting, colliding, and merging stars, to interpret the rapidly increasing number of observations of transients and to ultimately create a new model of stellar evolution.
Octo-Tiger is currently optimized 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.
The research outlines the current and planned areas of development aimed at tackling a number of physical phenomena connected to observations of transients.
The video by Sagiv Shriber, found here: https://lsu.app.box.com/s/9g41cbz14l2agk3etx0pxy8ityddknty, shows a simulation of the motion of two white dwarfs in each other’s orbits. We are looking down at these two stars as they begin to merge together.
The collaborative Octo-Tiger project continues, and we look forward to their novel and exciting work in now and in the future.
- Octo-Tiger is funded by: National Science Foundation Award1814967
- The following computational sources were utilzed to conduct the research: QueenBee2 at Louisiana Optical NetworkInitiative (LONI); BigRed3 at Indiana University was supported by Lilly Endowment, Inc., through its support for the Indiana University Pervasive Technology Institute; and Gadi from the National Computational Infrastructure (NCI Australia), an NCRIS enabled capability supported by the Australian Government.
