Summer Series. Supernovas, the explosions of stars at the end of life, contain valuable information about the origin of the universe. Master’s student Alexis Arnaudon seeks to improve parameters of their simulation to lift the veil on some of the many remaining questions about them.
Some stars end their lives dramatically. They explode in a halo of light as extremely intense as it is brief – as in, milliseconds. This grand finale, called a supernova, occurs particularly with massive stars that have more than 100 times the mass of the sun.
The explosion produces light but simultaneously rejects iron, calcium, sodium, and other heavy elements from the periodic table of elements. Since it is very rare to observe the explosion of a star, it is often from these chemical elements released into the universe that astrophysicists trace, in function of elapsed time, the number and type of supernovae that have exploded. To shed light on the many questions that remain regarding this difficult-to-observe phenomenon, researchers rely on simulations and theoretical models of all the physical processes present (gravity, momentum, cooling gas, etc.).
For his master’s thesis Alexis Arnaudon is interested in improving simulation software on EPFL’s supercomputer, primarily targeting supernovae in dwarf galaxies. These aggregations of around 10 billion stars (versus 200 to 400 billion for large galaxies) are of particular interest for research on the origin of the formation of galaxies due to their relatively independent evolution from the rest of the universe. Their small mass preserves them from numerous collisions with other galaxies.
Arnaudon began by replicating the explosion of an isolated star. The goal was to correct some faults of the program and to improve resolution. Using a new supernovae model, he also calibrated the software to reproduce the galaxies already observed, Fornax and Carina. These results are a first step toward achieving more accurate models.
This phenomenon, which can occur two to three times per century in the Milky Way alone, constitutes a force that is the most destructive and creative in the universe. The shock wave from the supernova promotes the formation of new stars by initiating or accelerating the contraction of regions in the interstellar medium. And these chain reactions begin a process that forms stars, planets, and – why not? It happened on Earth – plants, air, and so on. “We now know that the vast amount of material and energy they eject is fundamental to creating a new galaxy,” explains the student.