Simulated supernovae match many observations but lack diversity
21 January 2016
Supernovae are dramatic explosions that occur at the end of the lives of certain types of star. These events are intensely energetic, ejecting debris with speeds of tens-of-thousands of kilometers per second and radiating, albeit briefly, with luminosities billions of times greater than our Sun. The energy and material ejected by supernovae have a key role in the evolution and chemical history of galaxies, and the brightness of supernovae means that it is feasible to observe them at great distances and use them to probe the expansion history of our Universe. However, we still lack a complete understanding of the nature of supernovae: which stars explode, and why? In an ongoing attempt to answer such questions, astronomers within CAASTRO, and around the world, are studying supernovae using a combination of observational campaigns, such as the SkyMapper supernova survey, and theoretical simulations of explosion physics.
As part of an international research team, Dr Stuart Sim (CAASTRO Associate Investigator, Queen’s University Belfast) and Dr Ivo Seitenzahl (CAASTRO Associate Investigator, ANU) led two studies that help make the link between theoretical ideas and observed properties of supernovae. Their work focuses on so-called "Type Ia" supernovae. These supernovae are thought to result from the explosion of white dwarf stars, but the means by which the explosion is triggered is widely debated. One of the leading models for Type Ia supernovae is the "Chandrasekhar mass delayed-detonation" scenario in which explosion occurs as a result of a white dwarf star increasing in mass due to transfer of material from a main-sequence (or giant) companion star in a binary system. In their publications, the team (also including CAASTRO Associate Investigator Dr Ashley Ruiter, ANU) presents the first set of theoretical predictions for light curves and spectra from a set of full three-dimensional hydrodynamical simulations of the delayed-detonation model. These synthetic observables can be compared to real data to judge the success of the theoretical models.
The researchers found that the full explosion models are remarkably successful in explaining many observed properties: although imperfect, the match to many observed features in the optical spectra of real supernovae is remarkable, and variations due to the orientation from which the supernova is observed can explain some of the observed differences between supernovae. However, the set of models considered do not yet account for the full range of observed properties of Type Ia supernovae. Building on this work, the team is now focused on extending their studies to alternative theoretical models and identifying the best way to use modern observations to distinguish between models.