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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

admin2015-04-10  93
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.
If there were no mysterious force at work across the great distance, what would happen to the universe?
选项 A、It would break the will of gravity.
B、It would be reined by gravity.
C、It would get into a mess.
D、It would expand at a faster rate.
答案B
解析 如果在浩瀚宇宙中没有这种神秘的力量，宇宙将会发生什么?[A]万有引力的作用将被打破。[B]万有引力将主宰整个宇宙。[C]宇宙将变得一团糟。[D]宇宙将以更快的速度膨胀。文章第三段指出，数十年来天文学家们一直知道宇宙在膨胀，但在20世纪90年代后期，他们开始意识到这种膨胀的速率在急剧加大。这表明某种神秘的、未被发现的力在浩瀚的宇宙中起作用，打破了万有引力的作用；如果没有这种力，万有引力最终将会是整个宇宙的主宰力量。由此可知，[B]符合这个意思，是正确答案。[A]与原文相比，偷换了主语；[C]在文章中没有提及．[D]正好与问题所问的意思相反。
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