A team of international astronomers harnessed the formidable computing power of Lawrence Berkeley National Laboratory in the U.S.A. and the National Astronomical Observatory of Japan, utilizing over five million supercomputer computing hours. After years of unwavering dedication to research, they have successfully crafted the inaugural high-resolution 3D radiation hydrodynamics simulations for extraordinary supernovae. This groundbreaking discovery will be featured in the forthcoming edition of The Astrophysical Journal.
Supernova explosions mark the dramatic conclusion of massive stars’ life cycles, releasing a brilliance equal to billions of suns in a self-destructive display. These spectacular events illuminate the cosmos and eject heavy elements formed within the stars, providing the foundation for new stars, planets, and playing a pivotal role in life’s origins. Consequently, supernovae have emerged as a leading focus in contemporary astrophysics, encompassing a multitude of significant astronomical and physical inquiries, both in theory and observation, holding profound research significance.
Over the past half-century, research has offered a relatively comprehensive understanding of supernovae. However, recent extensive supernova survey observations have unveiled numerous atypical stellar explosions, known as exotic supernovae, challenging and reshaping established knowledge of supernova physics.
Mysteries of Exotic Supernovae
Among these exotic supernovae, superluminous supernovae and eternally luminous supernovae stand as the most confounding. Superluminous supernovae exhibit a brightness approximately 100 times that of regular supernovae, which typically maintain their brightness for only a few weeks to 2-3 months. In contrast, the recently discovered eternally luminous supernovae can sustain their brightness for several years or even longer.
Even more astonishing is the irregular and intermittent brightness variations observed in a few exotic supernovae, resembling fountain-like eruptions. These peculiar supernovae may hold the key to comprehending the evolution of the most massive stars in the universe.
Origins and Evolutionary Structures
The origins of these exotic supernovae remain partially understood, but astronomers hypothesize they may originate from unusual massive stars. Stars with masses ranging from 80 to 140 times that of the Sun, as they near the end of their lifecycle, undergo carbon fusion reactions in their cores. During this process, high-energy photons can generate electron-positron pairs, triggering core pulsations and violent contractions.
These contractions release immense fusion energy, initiating explosions and resulting in significant eruptions within the stars. These eruptions can resemble regular supernova explosions. Additionally, collisions between materials from different eruption periods could produce phenomena akin to superluminous supernovae.
Currently, such massive stars in the universe are relatively rare, aligning with the scarcity of peculiar supernovae. Scientists suspect that stars with masses ranging from 80 to 140 times that of the Sun are highly likely progenitors of peculiar supernovae. However, the unstable evolutionary structures of these stars pose significant modeling challenges, with current models primarily restricted to one-dimensional simulations.
Limitations of Previous Models
Previous one-dimensional models exhibited significant shortcomings. Supernova explosions generate substantial turbulence, and turbulence profoundly influences supernova explosion dynamics and brightness. However, one-dimensional models are inadequate for simulating turbulence from first principles. These challenges have kept unraveling the physical mechanisms behind exotic supernovae a major challenge in current theoretical astrophysics.
A Leap in Simulation Capabilities
Simulating supernova explosions at high resolution posed immense challenges. As the simulation scale increased, maintaining high resolution became increasingly difficult, escalating complexity, computational demands, and necessitating the consideration of numerous physical processes. Ke-Jung Chen emphasized that their team’s simulation code held advantages over competing groups in Europe and America.
Previous simulations were mainly confined to one-dimensional and a few two-dimensional fluid models. However, in exotic supernovae, multidimensional effects and radiation play a pivotal role, significantly impacting light emissions and overall explosion dynamics.
The Power of Radiation Hydrodynamics Simulations
Radiation hydrodynamics simulations factor in radiation propagation and its interactions with matter. The intricate process of radiation transport makes calculations exceptionally challenging, with computational requirements and difficulties surpassing those of fluid simulations. Nevertheless, leveraging their team’s extensive experience in modeling supernova explosions and running large-scale simulations, they successfully produced the world’s first three-dimensional radiation hydrodynamics simulations of exotic supernovae.
Findings and Implications
The research team’s findings shed light on intermittent eruptions in massive stars, demonstrating characteristics akin to multiple subdued supernovae. Collisions between materials from different eruption periods can convert approximately 20-30% of the gas kinetic energy into radiation, elucidating the phenomenon of superluminous supernovae.
Moreover, the radiation cooling effect causes the erupted gas to form a dense yet uneven three-dimensional sheet structure. This sheet layer becomes the primary source of light emission in the supernova. Their simulation results effectively account for the observational features of the exotic supernovae mentioned earlier.
Through cutting-edge supercomputer simulations, this study makes significant strides in understanding the physics of exotic supernovae. As next-generation supernova survey projects commence, astronomers will detect more exotic supernovae, further enhancing our comprehension of the final stages of massive stars and their explosion mechanisms.
Reference: “Multidimensional Radiation Hydrodynamics Simulations of Pulsational Pair-instability Supernovae” by Ke-Jung Chen, Daniel J. Whalen, S. E. Woosley, and Weiqun Zhang, published on 14th September 2023 in The Astrophysical Journal. DOI: 10.3847/1538-4357/ace968.