Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan.
Nature. 2010 Jul 1;466(7302):82-5. doi: 10.1038/nature09122.
Type Ia supernovae form an observationally uniform class of stellar explosions, in that more luminous objects have smaller decline-rates. This one-parameter behaviour allows type Ia supernovae to be calibrated as cosmological 'standard candles', and led to the discovery of an accelerating Universe. Recent investigations, however, have revealed that the true nature of type Ia supernovae is more complicated. Theoretically, it has been suggested that the initial thermonuclear sparks are ignited at an offset from the centre of the white-dwarf progenitor, possibly as a result of convection before the explosion. Observationally, the diversity seen in the spectral evolution of type Ia supernovae beyond the luminosity-decline-rate relation is an unresolved issue. Here we report that the spectral diversity is a consequence of random directions from which an asymmetric explosion is viewed. Our findings suggest that the spectral evolution diversity is no longer a concern when using type Ia supernovae as cosmological standard candles. Furthermore, this indicates that ignition at an offset from the centre is a generic feature of type Ia supernovae.
Ia 型超新星形成了一类观测上均匀的恒星爆炸，因为更亮的物体具有更小的下降率。这种单参数行为使得 Ia 型超新星能够被校准为宇宙学的“标准烛光”，并导致了对加速宇宙的发现。然而，最近的研究表明，Ia 型超新星的真实性质更为复杂。从理论上讲，有人认为最初的热核火花是在白矮星前身的中心之外点燃的，可能是爆炸前对流的结果。从观测上看，Ia 型超新星的光谱演化超出了光度下降率关系所显示的多样性是一个尚未解决的问题。在这里，我们报告说，这种光谱多样性是由于从不对称爆炸的随机方向观察到的结果。我们的发现表明，当使用 Ia 型超新星作为宇宙学标准烛光时，光谱演化多样性不再是一个问题。此外，这表明从中心偏移点火是 Ia 型超新星的一个普遍特征。
