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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.
Scientists devote themselves to studying the supernovae prior to their explosion because
选项 A、the search for supernova stars can support existing theory of supernova mechanics.
B、what the pre-supernova stars looked like is related to the elements in the universe.
C、searching for the pre-supernova stars is extremely important for human development.
D、the search for pre-supernova stars can help probing into expansion in universe.
答案B
解析 科学家们致力于研究超新星爆炸之前的情况，原因在于[A]探索超新星可以支持现有的超新星构成理论。[B]超新星爆炸之前的状况与宇宙的构成要素有关。[C]探索爆炸之前的超新星对人类的发展至关重要。[D]探索爆炸之前的超新星有助于探究宇宙的膨胀。文章第一段指出，了解这些能燃烧的星体非常重要，部分原因是因为它们创造了宇宙中的大部分元素，包括构成人、植物及行星等的要素，所以，正确答案为[B]。[A]偷换了主语，是一个考察队探究超新星爆炸前的状况，他们的新发现证实了现存的超新星构成理论，而不是对超新星的探索可以支持现有的超新星构成理论；[C]不具体，它只是说“超新星对人类的发展至关重要”，但并没有具体说明如何重要．[D]不正确，文章第三段提及天文学家们知道宇宙一直在膨胀，但并没有说探索超新星有助于探究宇宙膨胀。
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