My research centers around unraveling the mystery of how massive stars explode at the end of their lives. Such core-collapse supernova explosions are responsible for the production of most of the elements beyond hydrogen and helium throughout the Universe and play a crucial role in providing feedback mechanisms to galaxy and star formation. While supernovae are observed routinely to occur in galaxies near and far, the physical mechanism that drives these energetic explosions remains unclear. My study of the core-collapse supernova mechanism uses cutting-edge computational methods executed on the world's largest supercomputers.
The most promising candidate for the supernova explosion mechanism is the so-called “delayed neutrino heating” mechanism. Neutrinos carry away nearly all of the gravitational binding energy released via the collapse of the stellar core, about 100 times the energy necessary to drive robust supernova explosions. The trouble is that neutrinos have an incredibly tiny cross section for interaction, making extracting much of this copious energy extremely difficult. The most sophisticated 1D simulations have, for decades, shown that the neutrino mechanism fails in spherical symmetry. The situation is somewhat more promising in 2D and 3D wherein a handful of self-consistent explosions have been obtained, but these explosions tend to be marginal.
Much of my recent work has focussed on the role of turbulence in the supernova mechanism. Turbulence behind the stalled supernova shock, driven by the neutrino heating, is extremely strong and violent. This turbulence exerts an effective pressure on the stalled shock that can revival the background thermal pressure. This is a huge effect that is completely missing from 1D calculations! My collaborators and I showed that 2D and 3D calculations require much less neutrino heating to reach explosions precisely because of this turbulent pressure helping to push the shock out. I am currently investigating the requirements for accurately modeling turbulence in the simulations of the supernova mechanism.
Another aspect of my research is understanding how convection in the cores of supernova progenitor stars can influence the explosion mechanism. How strong such convection is in real massive stars was uncertain since the state-of-the-art in supernova progenitor calculations is still 1D models. My collaborators and I made the first steps forward in addressing these issues by carrying out the world's first 3D supernova progenitor simulation, directly calculating the final three minutes in the life of a massive star all the way to the point of gravitational core collapse. We showed that the resulting strongly aspherical progenitor structure was more favorable for successful CCSN explosion than an otherwise identical 1D progenitor.
Together with my collaborators around the country, I am leading a cutting edge effort to produce the world's first and most realistic 3D supernova progenitor models. This work involves the combination of best-in-class open-source stellar evolution modeling codes with a 3D nuclear combustion hydrodynamics code, and the world's fastest supercomputers.
Selected PublicationsS.M. Couch, E. Chatzopoulos, W.D. Arnett, F.X. Timmes 2015, “The Three-dimensional Evolution to Core Collapse of a Massive Star,” Astrophysical Journal Letters, 808, L21
S.M. Couch, C.D. Ott 2015, “The Role of Turbulence in Neutrino-driven Core-collapse Supernova Explosions,” Astrophysical Journal, 799, 5
S.M. Couch, E.P. O’Connor 2014, “High-resolution Three-dimensional Simulations of Core-collapse Supernovae in Multiple Progenitors,” Astrophysical Journal, 785, 123
S.M. Couch, C.D. Ott 2013, “Revival of the Stalled Core-collapse Supernova Shock Triggered by Precollapse Asphericity in the Progenitor Star,” Astrophysical Journal Letters, 778, L7