G. C. Jordan IV, C. Graziani, R. T. Fisher, D. M. Townsley, C. Meakin, K. Weide, L. B. Reid, J. Norris, R. Hudson, D. Q. Lamb
We describe the detonation mechanism comprising the "Pulsationally Assisted"
Gravitationally Confined Detonation (GCD) model of Type Ia supernovae (SNe Ia).
This model is analogous to the previous GCD model reported in Jordan (2008);
however, the chosen initial conditions produce a substantively different
detonation mechanism, resulting from a larger energy release during the
deflagration phase. The resulting final energy releases and nickel-56 yields
conform better to observational values than is the case for the "classical" GCD
models. In the present class of models, the ignition of a deflagration phase
leads to a rising, burning plume of ash. The ash breaks out of the surface of
the white dwarf, flows laterally around the star, and converges on the
collision region at the antipodal point from where it broke out. The amount of
energy released during the deflagration phase is enough to cause the star to
rapidly expand, so that when the ash reaches the antipodal point, the surface
density is too low to initiate a detonation. Instead, as the ash flows into the
collision region (while mixing with surface fuel) the star reaches its
maximally expanded state and then contracts. The stellar contraction acts to
increase the density of the star, including the density in the collision
region. This both raises the temperature and density of the fuel-ash mixture in
the collision region and ultimately leads to thermodynamic conditions that
produce a detonation. We demonstrate this mechanism with three 3-dimensional
(3D), full star simulations of this model using the FLASH code, varying the
initial offset of the ignition points for each model. The simulations are
characterized by nuclear energy releases ranging from 38% to 78% of the binding
energy of the white dwarf during the deflagration phase. We show that the
conditions for detonation are achieved in all three of the models.
View original:
http://arxiv.org/abs/1202.3997
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