2. 外语
  3. Upwards of a billion stars in our galaxy have burnt up their internal energy sources, and so can no longer produce the heat a st

Upwards of a billion stars in our galaxy have burnt up their internal energy sources, and so can no longer produce the heat a st

admin2010-06-18  59
问题    Upwards of a billion stars in our galaxy have burnt up their internal energy sources, and so can no longer produce the heat a star needs to oppose the inward force of gravity. These stars, Of more than a few solar masses, evolve, in general, much more rapidly than does a star like the Sun. Moreover, it is just these more massive stars whose collapse does not halt at intermediate stages (that is, as white dwarfs of neutron stars), Instead, the collapse continues until a singularity (an infinitely dense concentration of matter) is reached.
   It would be wonderful to observe a singularity and obtain direct evidence of the undoubtedly bizarre phenomena that occur near one. Unfortunately in most cases a distant observer cannot see the singularity: outgoing light rays are dragged back by gravity so forcefully that even if they could start out within a few kilometers of the singularity, they would end up in the singularity itself.
The author’s primary purpose in the passage is to ______.
选项 A、describe the formation and nature of singularities
B、explain why large numbers of stars become singularities
C、compare the characteristics of singularities with those of stars
D、imply that singularities could be more easily studied if observers could get closer to them
答案A
解析
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