An international team of astronomers took advantage of powerful supercomputers at Lawrence Berkeley National Laboratory in the United States and the National Astronomical Observatory in Japan. After years of painstaking research and more than five million supercomputer computing hours, they finally created the world's first high-resolution three-dimensional radiation hydrodynamics simulation of a bizarre supernova. The discovery will be published in the latest issue of The Astrophysical Journal.
Three-dimensional simulations of exotic supernovae reveal the turbulent structures created during the ejection of material in the explosion. These turbulent structures then influence the overall supernova's brightness and explosion structure. Turbulence plays a crucial role during supernova explosions and is caused by irregular fluid motions, leading to complex dynamics. These turbulent structures mix and distort matter, affecting the release and transfer of energy, thereby affecting the brightness and appearance of the supernova. Through three-dimensional simulations, scientists have a deeper understanding of the physical processes of strange supernova explosions and can explain the observed phenomena and characteristics of these extraordinary supernovae. Source: Ke-JungChen/ASIAA
Supernova explosions are the most spectacular endings of massive stars. They end their life cycles by self-destruction, instantly releasing a brightness equivalent to billions of suns, illuminating the entire universe. During the explosion, heavy elements formed inside the star are also ejected, laying the foundation for the birth of new stars and planets, and playing a vital role in the origin of life. Therefore, supernovae have become one of the frontier topics of modern astrophysics, covering many important astronomical and physical issues in theory and observation, and have important research value.
Over the past half century, research has given us a relatively comprehensive understanding of supernovae. However, the latest large-scale supernova survey observations are beginning to reveal many unusual stellar explosions (bizarre supernovae) that challenge and overturn previously established understandings of supernova physics.
The Mystery of a Strange Supernova
Among the strange supernovae, superluminous supernovae and eternally luminous supernovae are the most puzzling. Superluminous supernovae are about 100 times brighter than ordinary supernovae, while the brightness of ordinary supernovae usually only lasts for a few weeks to 2-3 months. In contrast, recently discovered eternally glowing supernovae can maintain their brightness for several years or more.
Even more surprising is that some strange supernovae show irregular and intermittent changes in brightness, erupting like fountains. These strange supernovae may hold the key to understanding the evolution of the most massive stars in the universe.
This picture depicts the final physical distribution of strange supernovae. The four quadrants of different colors represent different physical quantities: I. Temperature; II. Speed; III. Radiation energy density; IV. Gas density. The white dashed circle indicates the location of the supernova photosphere. As you can see from this image, the entire star becomes turbulent from the inside out. The locations where the ejected material collided closely matched the positions of the photospheres, suggesting that thermal radiation was produced during these collisions, effectively propagating outward while creating a non-uniform layer of gas. This image helps us understand the basic physics of strange supernovae and provides an explanation for the observed phenomena. Source: Ke-JungChen/ASIAA
Origin and evolutionary structure
The origins of these bizarre supernovae are not entirely understood, but astronomers believe they may arise from unusually massive stars. For stars with masses between 80 and 140 times that of the sun, carbon fusion reactions occur in their cores as they near the end of their lives. In the process, high-energy photons create electron-positron pairs, triggering pulsations in the core that cause several violent contractions.
These contractions release large amounts of fusion energy and trigger explosions, leading to massive star explosions. The bursts themselves may resemble ordinary supernova explosions. In addition, when matter in different explosion stages collide, a phenomenon similar to a superluminal supernova may occur.
Currently, the number of such massive stars in the universe is relatively rare, which is consistent with the scarcity of exotic supernovae. Therefore, scientists suspect that stars with masses 80 to 140 times that of the sun are most likely the ancestors of strange supernovae. However, the unstable evolving structure of these stars makes their modeling quite challenging, and current models are mainly limited to one-dimensional simulations.
Limitations of previous models
However, previous one-dimensional models also have serious shortcomings. Supernova explosions create a lot of turbulence, and turbulence plays a crucial role in the explosion and brightness of supernovae. However, one-dimensional models cannot simulate turbulence from first principles. These challenges make in-depth understanding of the physical mechanisms behind strange supernovae still a major problem in current theoretical astrophysics.
A leap in simulation capabilities
High-resolution simulations of supernova explosions pose significant challenges. As the scale of simulations increases, maintaining high resolution becomes increasingly difficult, greatly increasing complexity and computational requirements while also requiring a large number of physical processes to be considered. Chen Kezheng emphasized that their team’s simulation code has advantages compared with other competing groups in Europe and the United States.
Previous relevant simulations were mainly limited to one-dimensional and a few two-dimensional fluid models, while in exotic supernovae, multidimensional effects and radiation play a crucial role, affecting the optical radiation and the overall dynamics of the explosion.
The power of radiation hydrodynamics simulations
Radiation hydrodynamics simulations take into account radiation propagation and its interaction with matter. This intricate radiative transfer process makes calculations extremely challenging, and its computational requirements and difficulty are much higher than those of fluid simulations. However, with the team's extensive experience in supernova explosion modeling and large-scale simulation runs, they finally succeeded in creating the world's first three-dimensional radiation hydrodynamics simulation of a bizarre supernova.
Research findings and implications
The team's findings suggest that intermittent explosions of massive stars can exhibit characteristics similar to multiple fainter supernovae. When materials from different explosion stages collide, about 20%-30% of the kinetic energy of the gas can be converted into radiation, which is the cause of the superluminal supernova phenomenon.
In addition, the radiative cooling effect causes the ejected gas to form a dense but uneven three-dimensional sheet structure. This sheet structure becomes the main light emission source of the supernova. Their simulation results effectively explain the observed characteristics of the above-mentioned strange supernovae.
Using cutting-edge supercomputer simulations, the research provides significant progress in understanding the physics of bizarre supernovae. With the launch of the Next Generation Supernova Survey, astronomers will detect more exotic supernovae, further deepening our understanding of the final stages of typically massive stars and their explosion mechanisms.