Kasen D, Röpke F K, Woosley S E
Department of Astronomy and Astrophysics, UCSC, Santa Cruz, California 95064, USA.
Nature. 2009 Aug 13;460(7257):869-72. doi: 10.1038/nature08256.
Type Ia supernovae result when carbon-oxygen white dwarfs in binary systems accrete mass from companion stars, reach a critical mass and explode. The near uniformity of their light curves makes these supernovae good 'standard candles' for measuring cosmic expansion, but a correction must be applied to account for the fact that the brighter ones have broader light curves. One-dimensional modelling, with a certain choice of parameters, can reproduce this general trend in the width-luminosity relation; but the processes of ignition and detonation have recently been shown to be intrinsically asymmetric, so parameterization must have its limits. Here we report multi-dimensional modelling of the explosion physics and radiative transfer, which reveals that the breaking of spherical symmetry is a critical factor in determining both the width-luminosity relation and the observed scatter about it. The deviation from spherical symmetry can also explain the finite polarization detected in the light from some supernovae. The slope and normalization of the width-luminosity relation has a weak dependence on certain properties of the white dwarf progenitor, in particular the trace abundances of elements other than carbon and oxygen. Failing to correct for this effect could lead to systematic overestimates of up to 2 per cent in the distance to remote supernovae.
Ia型超新星是在双星系统中的碳氧白矮星从伴星吸积物质、达到临界质量并爆炸时产生的。它们的光变曲线近乎一致，这使得这些超新星成为测量宇宙膨胀的良好“标准烛光”，但必须进行校正，以考虑到较亮的超新星具有更宽的光变曲线这一事实。通过特定参数选择的一维建模可以重现宽度-光度关系中的这一总体趋势；但最近研究表明，点火和爆轰过程本质上是不对称的，因此参数化必然存在局限性。在此，我们报告了爆炸物理和辐射传输的多维建模，结果表明球对称性的破缺是决定宽度-光度关系及其观测到的散点的关键因素。与球对称性的偏差还可以解释在一些超新星的光中检测到的有限偏振。宽度-光度关系的斜率和归一化对白矮星前身星的某些性质有微弱的依赖性，特别是碳和氧以外元素的痕量丰度。不校正这种效应可能导致对遥远超新星距离的系统性高估，最高可达2%。
