A series of two-dimensional numerical simulations of explosive nuclear burning is presented for white dwarfs near the Chandrasekhar mass. We assume that the burning begins as a slow deflagration front at or near the center of the star and continues until the density in the burning regions has declined to about 107 g cm–3, where the flame is essentially extinguished. We employ a novel numerical representation of the turbulent flame brush based upon ideas previously developed for modeling laboratory combustion and explore in some detail the sensitivity of the outcome to the manner in which burning is initiated. In particular, we simulate (1) a centrally ignited deflagration, (2) off-center ignition at a single "point," and (3) simultaneous off-center ignition at five "points." We find that the amount of 56Ni that is produced and other observable properties depend sensitively upon how the fuel is ignited. Because of the immediate onset of buoyant acceleration, the burning region in models ignited off center rises toward the surface more quickly than in the (commonly assumed) case of central ignition. With the exception of the model that ignited off-center at a single point, all models are unbound at the end of the computations, and between 0.59 M☉ (central ignition) and 0.65 M☉ (ignition at multiple "points") of matter are processed into nuclear-burning products. These results would guarantee an observable, though weak, Type Ia supernova. Our results are expected to change for simulations in three dimensions, especially for the off-center ignitions discussed in this paper, and late detonations driven by pulsations are not unambiguously excluded. We can, however, state that the chances for a direct transition to a detonation appear small because, in all our models, the turbulent velocity of the burning front remains very subsonic.
展开▼
机译：针对Chandrasekhar地块附近的白矮星，提出了一系列爆炸性核燃烧的二维数值模拟。我们假设燃烧以恒星中心或附近恒星的缓慢爆燃开始，一直持续到燃烧区域的密度下降到约107 g cm–3为止，在那里火焰基本熄灭。我们基于先前为实验室燃烧建模而开发的思想，采用了湍流火焰刷的新颖数值表示形式，并在某些细节上探讨了结果对燃烧方式的敏感性。特别地，我们模拟（1）中央点火爆燃，（2）在一个“点”偏心点火，以及（3）在五个“点”同时偏心点火。我们发现，产生的56Ni的数量和其他可观察到的特性敏感地取决于燃料的点火方式。由于立即出现了浮力加速，因此与（通常假定的）中央点火情况相比，模型从中心点火的燃烧区域朝表面上升的速度更快。除了在单个点处偏心点火的模型外，所有模型在计算结束时都不受约束，并且在0.59M☉（中心点火）和0.65M☉（在多个“点”处点火）之间被加工成核燃烧产品。这些结果将保证可观测到的Ia型超新星，尽管强度较弱。对于三维模拟，我们的结果有望发生变化，尤其是本文讨论的偏心点火，并且不会明确排除由脉动驱动的后期爆震。但是，我们可以指出，直接转变为爆轰的机会似乎很小，因为在我们所有的模型中，燃烧前沿的湍流速度仍然非常超音速。
展开▼
