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  3. How is a newborn star formed? For the answer to this question, we must look to the familiar physical concept of gravitat

How is a newborn star formed? For the answer to this question, we must look to the familiar physical concept of gravitat

admin2012-01-15  120
问题         How is a newborn star formed? For the answer
    to this question, we must look to the familiar
    physical concept of gravitational instability. It is a
Line simple concept, long-known to scientists, having
(5) been first recognized by Isaac Newton in the late
     1600s.
        Let us envision a cloud of interstellar atoms
    and molecules, slightly admixed with dust. This
    cloud of interstellar gas is static and uniform.
(10) Suddenly, something occurs to disturb the gas,
    causing one small area within it to condense. As
    this small area increases in density, becoming
    slightly denser than the gas around it, its gravita-
    tional field likewise increases somewhat in
(15) strength. More matter now is attracted to the area,
    and its gravity becomes even stronger; as a result,
    it starts to contract, in the process increasing in den-
    sity even more. This in turn further increases its
    gravity, so that it accumulates still more matter
(20) and contracts further still. And so the process
    continues, until finally the small area of gas gives
    birth to a gravitationally bound object, a newborn
    star.
The author provides information that answers which of the following questions? Ⅰ. How does the small area’s increasing density affect its gravitational field? Ⅱ. What causes the disturbance that changes the cloud from its original static state? Ⅲ. What is the end result of the gradually increas-ing concentration of the small area of gas?
选项 A、Ⅰ only
B、Ⅱ only
C、Ⅰ and Ⅱ only
D、Ⅰ and Ⅲ only
E、Ⅰ, Ⅱ and Ⅲ
答案D
解析
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