Speaker
Description
The nature of stellar progenitors and the associated explosion mechanism of type Ia supernovae (SNIa) remains one of the major open questions in astrophysics. Virtually all existing theoretical models require formation of a supersonic
detonation wave capable of providing nearly complete incineration of the
stellar material of a WD after it becomes gravitationally unbound. The
mechanism of detonation initiation in unconfined systems, such as the interior
of a WD, remains poorly understood. Modern large-scale numerical models of SNIa
are unable to capture detonation formation from first principles due to the
extreme range of dynamical scales involved, and instead they are forced to
trigger detonations artificially. As a result, the time and location of the
detonation initiation are free parameters present in all existing SNIa models.
This limits predictive power of SNIa models and does not allow them to be
conclusively and rigorously confirmed or disproved using observations.
We discuss recent advances in our understanding of the physics of detonation
initiation in unconfined turbulent reacting flows, both terrestrial and
astrophysical. In particular, we present the general theory of
turbulence-induced deflagration-to-detonation transition (tDDT). We use direct
numerical simulations (DNS) of unconfined turbulent thermonuclear flames in a
degenerate 12C stellar plasma to show for the first time that under
conditions representative of those in a SNIa explosion this tDDT mechanism can
result in the spontaneous formation of strong shocks and subsequently
detonation ignition. We also describe results of experimental and numerical
studies in terrestrial chemical systems corroborating this theory. Finally, we
discuss the implications of this DDT theory for the classical single-degenerate
Chandrasekhar-mass model. These results open path for the new generation of the
first-principles predictive SNIa models, in which detonation initiation
conditions can be determined accurately and self-consistently.
