Simulations Reveal the Invisible Chaos of Superluminous Supernovae

“By modeling the star in 2D we can capture detailed information about fluid instability and mixing that you don’t get in 1D simulations. These details are important to accurately depict the mechanisms that cause the event to be superluminous and explain their corresponding observational signatures such as light curves and spectra.”

Chen is the lead author of an Astrophysical Journal paper published in December 2016. He notes that one of the leading theories in astronomy posits that superluminous supernovae are powered by highly magnetized neutron stars, called magnetars.

How a star lives and dies depends on its mass—the more massive a star, the more gravity it wields. All stars begin their lives fusing hydrogen into helium; the energy released by this process supports the star against the crushing weight of its gravity. If a star is particularly massive it will continue to fuse helium into heavier elements like oxygen and carbon, and so on, until its core turns to nickel and iron. At this point fusion no longer releases energy and electron degeneracy pressure kicks-in and supports the star against gravitational collapse. When the core of the star exceeds its Chandrasekhar mass—approximately 1.5 solar masses—electron degeneracy no longer supports the star. At this point, the core collapses, producing neutrinos that blow up the star and create a supernova.

This iron core-collapse occurs with such extreme force that it breaks apart nickel and iron atoms, leaving behind a chaotic stew of charged particles. In this frenzied environment negatively charged electrons are shoved into positively charged positrons to create neutral neutrons. Because neutrons now make up the bulk of this core, it’s called a neutron star. A magnetar is essentially a type of neutron star with an extremely powerful magnetic field.

In addition to being insanely dense—a sugar-cube-sized amount of material from a neutron star would weigh more than 1 billion tons—it is also spinning up to a few hundred times per second. The combination of this rapid rotation, density and complicated physics in the core creates some extreme magnetic fields.

Astrophysicist Ken Chen ran 2D simulations with Berkeley Lab’s CASTRO code on NERSC’s Edison supercomputer to better understand the physical conditions that create superluminious supernova.

Credit: Ken Chen, National Astronomical Observatory of Japan