Science2014-06-10 5:02 PM

为什么如此耀眼--解开超光亮超新星之谜 Detection of the Gravitational Lens Magnifying a Type Ia Supernova

论文摘要 

为什么如此耀眼--解开超光亮超新星之谜

据一项新的研究报告称,一颗格外明亮的超新星之所以如此明亮是因为位于其前方的一个“透镜”放大了它的光辉。关于这个“透镜”的发现解决了一个在天文学领域中的重要争议。2013年,一组科学家报告说,一颗叫做PS1-10afx的超新星的光芒比任何属于该部类的其它超新星都要更加明亮。它的超常的光辉令许多人困惑,从而让一些研究人员推断它是一种新型的超亮超新星,而也有人认为它是一颗被某种(在附近以超大质量黑洞形式存在的)透镜放大的 Ia 型超新星 (SNIa)。Robert Quimby及同事知道,如果有一个可放大超新星的引力透镜,那么在该超新星消褪之后,这个引力透镜将仍存在。因此,他们重新观测并获取新的、更好的数据以检验其特征,他们用Keck-I望远镜来观测PS1-10afx的寄主星系和邻近的星体。他们将来自PS1-10afx峰值亮度期的光谱数据与其消褪之后时期中的光谱数据进行了比较。如果在该光亮期有一个额外的星系与PS1-10afx重合,并作为“透镜”, 那么他们将会看到2组气体发射线--而这正是他们所观测到的情景。研究人员以这种方式推断,在PS1-10afx的正前方存在着另外一个星系--该星系恰好在合适的角度和距离放大了该超新星的光亮,从而起到了某种放大镜的作用。文章的作者说,这个“透镜”在先前的研究中被漏掉了,因为它的光消失在了其宿主星系中的超新星的明亮炫光之中。在此确定的透镜是第一个能强力放大Ia型超新星的透镜。由于Ia型超新星——其中包括该带透镜的类型——的行为可帮助科学家们测量至遥远星系的距离,这一新的发现可使得科学家们用未来的带透镜的超新星事件来测量宇宙的膨胀。

Abstract 

Objects of known brightness, like type Ia supernovae (SNIa), can be used to measure distances. If a massive object warps spacetime to form multiple images of a background SNIa, a direct test of cosmic expansion is also possible. However, these lensing events must first be distinguished from other rare phenomena. Recently, a supernova was found to shine much brighter than normal for its distance, which resulted in a debate: Was it a new type of superluminous supernova or a normal SNIa magnified by a hidden gravitational lens? Here, we report that a spectrum obtained after the supernova faded away shows the presence of a foreground galaxy—the first found to strongly magnify a SNIa. We discuss how more lensed SNIa can be found than previously predicted.

Editor's Summary

Magnified Flare-Up

The rise and fall of the luminosity of a supernova detected in 2010 was typical for its class, but its apparent brightness was 30 times greater than similar events. Quimby et al. (p. 396) compared spectra from the time of peak brightness and after the supernova faded, from which they concluded that something was interfering with our line of sight to the supernova. A previously unknown foreground galaxy turned out to be acting as a lens, bending and magnifying the light from the supernova. Potentially, spacetime warping like this could allow direct testing of cosmic expansion.

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