Max Planck Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85741 Garching, Germany.
Nature. 2010 Feb 18;463(7283):924-5. doi: 10.1038/nature08685.
There is wide agreement that type Ia supernovae (used as standard candles for cosmology) are associated with the thermonuclear explosions of white dwarf stars. The nuclear runaway that leads to the explosion could start in a white dwarf gradually accumulating matter from a companion star until it reaches the Chandrasekhar limit, or could be triggered by the merger of two white dwarfs in a compact binary system. The X-ray signatures of these two possible paths are very different. Whereas no strong electromagnetic emission is expected in the merger scenario until shortly before the supernova, the white dwarf accreting material from the normal star becomes a source of copious X-rays for about 10(7) years before the explosion. This offers a means of determining which path dominates. Here we report that the observed X-ray flux from six nearby elliptical galaxies and galaxy bulges is a factor of approximately 30-50 less than predicted in the accretion scenario, based upon an estimate of the supernova rate from their K-band luminosities. We conclude that no more than about five per cent of type Ia supernovae in early-type galaxies can be produced by white dwarfs in accreting binary systems, unless their progenitors are much younger than the bulk of the stellar population in these galaxies, or explosions of sub-Chandrasekhar white dwarfs make a significant contribution to the supernova rate.
人们普遍认为 Ia 型超新星（用作宇宙学的标准烛光）与白矮星的热核爆炸有关。导致爆炸的核失控可能始于白矮星逐渐从伴星积累物质，直到达到钱德拉塞卡极限，也可能由两个在紧凑双星系统中的白矮星合并触发。这两种可能途径的 X 射线特征非常不同。在合并情景中，直到超新星前不久，预计不会有强烈的电磁发射，而从正常恒星吸积物质的白矮星在爆炸前约 10(7) 年成为大量 X 射线的来源。这提供了一种确定哪种途径占主导地位的方法。在这里，我们报告说，根据它们的 K 波段光度估计的超新星率，观测到的六个近椭圆星系和星系隆起的 X 射线通量比吸积情景预测的低约 30-50 倍。我们的结论是，在早期星系中，只有不到 5%的 Ia 型超新星可以由吸积双星系统中的白矮星产生，除非它们的前身比这些星系中大部分恒星的年龄小得多，或者亚钱德拉塞卡白矮星的爆炸对超新星率有重大贡献。
