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  3. About 2,500 of so-called supernovae are known inside our galaxy and beyond. But exactly what they were before they exploded is n

About 2,500 of so-called supernovae are known inside our galaxy and beyond. But exactly what they were before they exploded is n

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问题     About 2,500 of so-called supernovae are known inside our galaxy and beyond. But exactly what they were before they exploded is not so clear. The hunt for supernovae, from their origins to their long-term effects, is heating up rapidly. Understanding these incendiary objects is important in part because they are responsible for creating most of the elements in the universe, including the stuff of which people, plants and planets are made. A supernova is relatively easy to detect because of the intense radiation it casts off in visible light and other wavelengths. Figuring out what the star looked like prior to the explosion, however, requires probing into the archives of astronomy.
    A separate team of supernova hunters did just that, using a decade of Hubble Space Telescope images to search for possible pre-supernova stars. Their new findings support existing theory of supernova mechanics, which holds that only very massive stars explode. When a massive star burns up all its hydrogen fuel, it casts its outer layers into space and then collapses into a dense neutron star or black hole. Theorists believe that stars must be about 10 to 20 times the mass of the sun to support such an explosive scenario. Such heavy objects have brief lives, typically less than 20 million years, compared with the sun, which is middle-aged and already 4. 6 billion years old.
Ground-based telescopes that observed the actual supernova explosions are not as accurate as Hubble, however, due to air turbulence, so scientists require follow-up Hubble observations to see if they are in the right positions. One has already been eliminated, Alexei Filippenko of the University of California at Berkeley said, but he’s confident at least a couple of the remaining five will prove to be actual precursor stars. Astronomers have known for decades that the universe is expanding. But in the late 1990s they began to realize that the expansion is occurring at an ever-faster rate. This suggests that some mysterious, unseen force is at work across great distances, breaking the will of gravity that would otherwise rein in the universe eventually.
    Supernovae are useful in this research because they can be seen from far away. Astronomers measure how much an exploded star’s light has stretched, which tells them the speed at which the object is receding. By comparing this to nearby supernovae, researchers can refine the universal expansion’s rate of acceleration. In particular, the orbiting observatory’s keen new eyesight can be used to analyze pinpricks of light from very distant objects and learn what they are and what they’re made of. This so-called spectroscopy technique is just like using a prism to break white light into its constituent colors.
The research of what supernovae were before they exploded can help researchers
选项 A、refine the universal expansion’s rate of acceleration.
B、measure how much an exploded star’s light has stretched.
C、analyze light from very distant objects.
D、find how the universe expands.
答案A
解析 研究超新星爆炸之前的状况能帮助研究人员[A]更精确地计算宇宙膨胀的加速率。[B]测量一颗爆炸星星的光的延伸距离。[C]分析来自遥远星体的光。[D]发现宇宙是如何膨胀的。文章最后一段指出，超新星在这项研究中的作用很大。天文学家们对一颗爆炸星星的光的延伸距离进行测量，这能告诉他们这个星体的衰减速度。将这与附近的超新星相比较，研究人员可以对宇宙膨胀的加速率进行更加精确的计算。这说明超新星的最终作用是使研究人员对宇宙膨胀的加速率的了解更加精确。[B]不正确，因为“测量一颗爆炸星星的光的延伸距离”是天文学家们正在进行的研究；[C]是轨道天文台的作用，不是超新星的作用；[D]文中没有提及。
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