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Detonability of white dwarf plasma: Turbulence models at transition densities

Published onJun 01, 2020
Detonability of white dwarf plasma: Turbulence models at transition densities

The deflagration-to-detonation transition (DDT) mechanism has been long studied, but remains one of the major unsolved problems of theoretical combustion. Astrophysicists have suspected for almost 40 years that it is also directly responsible for at least a subclass of white dwarf explosions powering Type Ia supernovae (SN Ia). Astrophysical observational evidence for the DDT is, however, only indirect, which hinders progress in understanding the SN Ia explosion mechanism. Regardless of whether or not the deflagration initially exists, the viable explosion mechanism requires conditions in which the flow is energized and sizeable parcels of fuel attain a critical burning temperature. The question then is, what is the source of that energy? One possibility might be turbulence existing in the white dwarf plasma. The importance of compressibility for formation of detonations in turbulent low white dwarf plasma was studied recently by our group. We found that in order to initiate detonations, the turbulence has to be strongly compressibly-driven. Alas, in stellar environments, this type of turbulence usually does not exist on secular timescales due to the lack of a sustained driving mechanism. However, one exception here is the violent phase of a binary white dwarf merger, in which the driving is provided by accretion flow from the secondary star. This phase lasts for about 100 seconds and provides ample time to sustain strongly compressible turbulence.In this work we consider the sensitivity of nuclear burning to the intensity of turbulence. In this work, we perform a series of well-resolved turbulence simulations of carbon-oxygen mixtures at densities relevant for DDT in single-degenerate SN Ia channel. We are systematically changing properties of turbulence and find a range of behaviors from non-explosive scenarios to cases with complete burning. We discuss the necessary conditions for DDT and offer SN Ia observables that could be used to confirm the proposed explosion mechanism.

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