An international team of astronomers used powerful supercomputers at Lawrence Berkeley National Laboratory in the United States and the National Astronomical Observatory of Japan. After years of intense research and more than 5 million supercomputer computational hours, they have finally created the world’s first high-resolution 3D radiative hydrodynamic simulation for an exotic supernova. This discovery will be published in the current issue. of astrophysical journal.
A supernova explosion is the most spectacular outcome for a massive star, ending its life in a self-destructive manner, instantly emitting as much brightness as billions of suns, illuminating the entire universe. During this explosion, heavy elements formed inside the star are also released, laying the foundation for the birth of new stars and planets, and playing an important role in the origin of life. Therefore, supernovae have become one of the cutting-edge topics in modern astrophysics, encompassing a number of important astronomical and physical problems, both theoretical and observational, and have important research value. Masu.
Research over the past half century has provided a relatively comprehensive understanding of supernovae. However, the latest large-scale supernova survey observations have begun to reveal a large number of unusual stellar explosions (exotic supernovae) that cast doubt on and overturn previously established knowledge of supernova physics.
The mystery of an exotic supernova
Of the exotic supernovae, hyperluminous supernovae and permanent luminous supernovae are the most complex. Ultra-bright supernovae are about 100 times brighter than normal supernovae, and typically remain bright for only a few weeks to a few months. In contrast, recently discovered permanently luminous supernovae can maintain their brightness for several years or even longer.
Even more surprising is that some exotic supernovae exhibit irregular and intermittent changes in brightness, resembling fountain-like eruptions. These unusual supernovae may hold the key to understanding the evolution of the universe’s most massive stars.
Origin and evolutionary structure
The origin of these exotic supernovae is still not fully understood, but astronomers believe they can originate from unusually massive stars. Stars with masses between 80 and 140 times the mass of the Sun undergo carbon fusion reactions in their cores toward the end of their lives. During this process, high-energy photons create electron-positron pairs that can cause pulsations within the nucleus and cause several violent contractions.
These contractions release huge amounts of fusion energy and cause explosions, resulting in massive eruptions in the star. These eruptions themselves can resemble regular supernova explosions. Additionally, collisions of material from different eruption periods can cause phenomena similar to superluminous supernovae.
Currently, the number of such massive stars in the universe is relatively rare, which is consistent with the rarity of unusual supernova explosions. Scientists therefore think that stars with masses in the range of 80 to 140 times that of the Sun are likely to be precursors to unusual supernovae. However, the unstable evolutionary structure of these stars makes their modeling very difficult, and current models are mainly limited to his one-dimensional simulations.
Previous model limitations
However, significant flaws were found in previous one-dimensional models. Supernova explosions generate significant turbulence, and turbulence plays an important role in the explosion and brightness of supernovae. Nevertheless, one-dimensional models are unable to simulate turbulence from first principles. Due to these challenges, a deep understanding of the physical mechanisms behind exotic supernovae remains a major problem in current theoretical astrophysics.
A breakthrough in simulation capabilities
High-resolution simulations of this supernova explosion were fraught with immense difficulties. As the scale of simulations increased, it became increasingly difficult to maintain high resolution, significantly increasing the complexity and computational demands, as well as requiring consideration of a large number of physical processes. Ke-Jung Chen emphasized that his team’s simulation code is superior to other competing groups in Europe and America.
Previous relevant simulations have been mainly limited to one-dimensional fluid models and some two-dimensional fluid models, but in exotic supernovae, multidimensional effects and radiation play an important role, and the luminescence and explosion Affects the overall dynamics.
The power of radial fluid dynamics simulation
Radiation hydrodynamics simulations consider the propagation of radiation and its interaction with matter. This complex process of radiation transport makes the calculations extremely difficult, with the computational requirements and difficulty level being much higher than fluid simulation. But because the team has extensive experience modeling supernova explosions and running large-scale simulations, they finally succeeded in creating the world’s first three-dimensional radiative hydrodynamic simulation of an exotic supernova.
Findings and implications
The researchers’ results show that intermittent eruptive events in massive stars can exhibit characteristics similar to fainter supernovae. When materials from different eruption times collide, about 20-30% of the kinetic energy of the gas is converted into radiation, explaining the hyperluminous supernova phenomenon.
Furthermore, due to the radiative cooling effect, the ejected gas forms a dense but inhomogeneous three-dimensional sheet structure, and this sheet layer becomes the main source of light in the supernova. Their simulation results effectively explain the observational features of the exotic supernova mentioned above.
This research represents a major step forward in gaining insight into the physics of exotic supernovae through cutting-edge supercomputer simulations. With the launch of the next generation of supernova research projects, astronomers will detect more exotic supernovae and further shape our understanding of the final stages of normal massive stars and their explosion mechanisms.
Reference: Ke-Jung Chen, Daniel J. Whalen, SE Woosley, Weiqun Zhang, “Multidimensional radiative hydrodynamic simulation of pulsating versus unstable supernovae,” September 14, 2023. astrophysical journal.
DOI: 10.3847/1538-4357/ace968