For the first time in the world, a three-dimensional simulation of a "supernova" has finally been achieved, which is 100 times brighter than a supernova!

[Mobile software: Bo Ke Yuan] For most of the 20th century, astronomers have been searching the sky for supernovas and their supernova remnants (supernovas are the explosive deaths of massive stars) for clues about stellar progenitors, the mechanisms that caused them to explode, and the creation of heavy elements in the process. In fact, these supernova events create most of the cosmic elements in the universe, which go on to form new stars, galaxies, and life. Because no one can actually see a supernova up close, researchers rely on supercomputer simulations to gain insight into the physical mechanisms that trigger and drive supernova explosions.

Now, for the first time ever, an international team of astrophysicists has simulated the three-dimensional (3-D) physics of a hypernova that is about 100 times brighter than a typical supernova. The milestone was achieved using Lawrence Berkeley National Laboratory's (Berkeley Lab) Castro code and the National Energy Research Scientific Computing Center (NERSC) supercomputers, and their results are published in the Astrophysical Journal. The astronomers found that these hypernova events occur when a magnetar - a star with a magnetic field trillions of times stronger than Earth's - is at the center of a young supernova.

Illustration: The nebula phase of a magnetar-driven supernova obtained from a 3D simulation; the supernova ejecta has now expanded to a size similar to that of the Solar System; large-scale mixing occurs both in the inner and outer regions of the ejecta; the resulting light curve and spectrum are sensitive to mixing, which depends on the stellar structure and the physical properties of the magnetar.

The radiation released by the magnetar amplifies the supernova luminosity, but to understand how this happens, researchers need multi-dimensional simulations. "To perform 3-D simulations of magnetar-driven supernovae requires a lot of supercomputing power and the right code, one that can capture the relevant microphysics," said Ken Chen, lead author of the study and an astrophysicist at the Institute of Astronomy and Astrophysics (ASIAA) of Academia Sinica in Taiwan. "The numerical simulations required to capture the fluid instabilities of these supernovae events in three dimensions are very complex. A lot of computing power is required, which is why no one has done this research before."

Fluid instabilities are seen everywhere, for example, if you have a glass of water and put some dye on it, the surface tension of the water becomes unstable and the heavier dye sinks to the bottom. The physics of this instability cannot be captured in one dimension as the two fluids flow past each other. A second or third dimension, perpendicular to the height, is needed to see all of the instabilities. On cosmic scales, fluid instabilities leading to turbulence and mixing play a key role in the formation of cosmic objects such as galaxies, stars and supernovae, which requires capturing physics across a range of scales at extremely high resolution.

Illustration: The turbulent core of the magnetic bubble inside a supernova, color-coded to show density. The magnetar is located in the center of this image, and two bipolar outflows are emitted from it. The physical size of the outflows is about 10,000 kilometers.

From the very large to the very small, it is necessary to accurately model astrophysical objects like superluminal supernovae. This poses a technical challenge for astrophysicists, which the study was able to overcome with a new numerical scheme and millions of supercomputing hours at NERSC. In this study, the researchers simulated a supernova remnant about 15 billion kilometers wide with a direct 10-kilometer magnetar inside it. In this system, the simulations showed that two scales of hydrodynamic instabilities form in the remnant. One instability is in the hot bubble powered by the magnetar, and the other occurs when the normal shock wave of the young supernova hits the surrounding gas.

These two fluid instabilities lead to more mixing than usually occurs in a typical supernova event, which has a major impact on the light curve and spectrum of the supernova. None of this is captured in a one-dimensional model, and neither of these situations occurs in a typical supernova event. The study also found that magnetars can accelerate calcium and silicon elements ejected by young supernovas to speeds of up to 12,000 kilometers per second, explaining the broadening of emission lines in spectral observations. Even energy from weak magnetars can accelerate iron-group elements deep in supernova remnants to 5,000 to 7,000 kilometers per second.

Illustration: The turbulent core of the magnetic bubble inside a supernova. The color coding shows the density. The magnetar is located in the center of this image. The strong turbulence is caused by the radiation from the central magnetar.

This explains why iron is observed very early in core-collapse supernova events like SN 1987A, a long-standing mystery in astrophysics. The research team is the first to accurately simulate a speeding supernova system in three dimensions, and is lucky to have access to the NERSC supercomputer, a facility that is an extremely convenient place to do cutting-edge science.

Boco Park | Research/From: National Energy Research Scientific Computing Center

Reference journal: Astrophysics

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