An international team of astronomers used powerful supercomputers from Lawrence Berkeley National Laboratory in the USA and the National Astronomical Observatory in Japan. After years of dedicated research and consuming more than five million hours of ultra-fast computing, they have finally created the world’s first high-resolution 3D radiohydrodynamic simulation of exotic supernovae! This result will appear in the latest issue of the
“gt-data-translation-attributes=”[“attribute”:”data-cmtooltip”, “format”:”html”]”>The Astrophysical Journal.
Supernova explosions are the most dramatic endings to massive stars, ending their life cycles in a self-destructive manner, instantly releasing a brightness equivalent to billions of suns, illuminating the entire universe. During this explosion, heavy elements formed inside the star are also ejected, laying the foundation for the birth of new stars and planets, and playing a crucial role in the origin of life. Therefore, supernovae have become one of the leading topics in modern astrophysics, which includes many important astronomical and physical issues in both theory and observation, and has great research value.
Over the past half century, research has provided us with a relatively comprehensive understanding of supernovae. However, the latest large-scale supernova observations have begun to reveal many unusual stellar explosions (exotic supernovae), which challenge and overturn previous knowledge of supernova physics.
Strange secrets of supernovas
Among the strange supernovae, the most puzzling are the superluminous supernovae and the eternally luminous supernovae. Superluminous supernovae are about 100 times as bright as ordinary supernovae, which typically only maintain their brightness for a few weeks to 2-3 months. In contrast, newly discovered supernovae can maintain their brightness for several years or even longer.
Even more surprising is that a few of the exotic supernovae exhibit irregular, intermittent variations in brightness, resembling fountain-like explosions. These strange supernovae may hold the key to understanding the evolution of the most massive stars in the universe.
Evolutionary origins and structures
The origins of these strange supernovae are still not fully understood, but astronomers believe they may originate from unusual massive stars. For stars between 80 and 140 times the mass of the Sun, as they approach the end of their lives, their cores undergo carbon fusion reactions. During this process, high-energy photons can create electron-positron pairs, triggering a heartbeat and triggering several violent contractions.
These contractions release huge amounts of fusion energy and trigger explosions, resulting in large explosions in stars. These explosions themselves could be similar to ordinary supernova explosions. Furthermore, when material from different eruption periods collide, it is possible to produce phenomena similar to extremely bright supernovae.
Currently, the number of such massive stars in the universe is relatively rare, which is consistent with the rarity of exotic supernovae. Therefore, scientists believe that stars with masses between 80 and 140 times the mass of the Sun are very likely the ancestors of exotic supernovas. However, the unstable evolutionary structures of these stars make their modeling very difficult, and current models remain mainly limited to one-dimensional simulations.
Limitations of previous models
However, serious shortcomings have been found in previous one-dimensional models. Supernova explosions generate large turbulence, and turbulence plays a crucial role in the explosion and brightness of supernovas. However, one-dimensional models are unable to simulate turbulence from first principles. These challenges have made gaining a deep understanding of the physical mechanisms behind exotic supernovae a major problem in current theoretical astrophysics.
A leap in simulation capabilities
These high-resolution simulations of supernova explosions presented enormous challenges. As the scale of simulation increases, maintaining high accuracy becomes increasingly difficult, greatly increasing complexity and computational requirements, while also requiring consideration of many physical processes. Ke-Jung Chen stressed that their team’s simulation program has advantages over other competing groups in Europe and America.
Previous relevant simulations were mainly limited to one-dimensional fluid models and a few two-dimensional fluid models, while in exotic supernovae, multi-dimensional effects and radiation play a crucial role, affecting light emission and overall explosion dynamics.
Force radiation hydrodynamic simulation
Radiohydrodynamic simulations take into account the propagation of radiation and its interactions with matter. This complex process of radiation transfer makes calculations very difficult, with much higher computational requirements and difficulties than fluid simulations. However, given the team’s rich experience in modeling supernova explosions and performing large-scale simulations; They have finally succeeded in creating the world’s first 3D radiohydrodynamic simulation of exotic supernovae.
Results and implications
The research team’s findings suggest that the phenomenon of intermittent explosions in massive stars could exhibit properties similar to multiple, faint supernovae. When materials from different eruption periods collide, approximately 20-30% of the kinetic energy of the gas can be converted into radiation, which explains the phenomenon of extremely bright supernovae.
Furthermore, the radiative cooling effect causes the explosive gas to form a dense, uneven 3D lamellar structure, and this layer of lamellar becomes the primary source of light emission in the supernova. Their simulation results effectively explain the observational features of the exotic supernovae mentioned above.
Through sophisticated supercomputer simulations, this study makes great strides in gaining insights into the physics of exotic supernovas. As next-generation supernova survey projects begin, astronomers will discover more exotic supernovae, further shaping our understanding of the final stages of ordinary massive stars and their explosion mechanisms.
Reference: “Multidimensional Radiohydrodynamic Simulation of Unstable Pulsed Supernovae” by Ke-Jung Chen, Daniel J. Whalen, S. E. Woosley, and Weiqun Zhang, 14 September 2023, Astrophysical Journal.
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