ZT:天文学-Brown Dwarf


天文学
Brown Dwarf

1. What is the main purpose of the lecture?

  • A. To explain methods astronomers use to classify stars 
  • B. To explain the formation of molecular clouds in the universe
  • C. To discuss how some stellar embryos fail to become stars  
  • D. To discuss similarities between brown dwarfs and planets

2. According to the professor, why is the study of brown dwarfs particularly challenging?

  • A. They cannot be detected directly.
  • B. They combine characteristics of very distinct celestial objects.
  • C. They appear in colors ranging from brown to red.
  • D. They are always near very bright stars.

3. Why does the professor discuss how stars originate?

  • A. To explain how brown dwarfs begin to form
  • B. To suggest that brown dwarfs do not originate in molecular clouds 
  • C. To explain why brown dwarfs emit light billions of years
  • D. To show that stellar embryos cause turbulence within molecular clouds

4. According to the ejection theory, why do some stellar embryos stop growing before they become stars?

  • A. The motion of dust and gas inhibits their growth.
  • B. The cores in which they form are not dense enough.
  • C. They start forming in the area of a molecular cloud with the least amount of material.
  • D. They are moved by gravitational forces to areas outside cores.

5. Why does the professor mention that newborn stars are surrounded by disks of dust and gas?

  • A. To describe a method for testing two theories about brown dwarfs 
  • B. To clarify how brown dwarfs are drawn into star systems 
  • C. To emphasize that brown dwarfs move at low velocities 
  • D. To introduce planet formation as the topic of the next lecture

6. What is the professor’s attitude toward the two theories?

  • A. He is convinced that neither of them can explain why brown dwarfs have stellar disks.
  • B. He hopes both theories will be confirmed by computer simulations.
  • C. He thinks evidence supports the turbulence theory even if he cannot rule out the ejection theory.
  • D. He finds the ejection theory more attractive than the turbulence theory.


答案:C  B  A  D  A  C

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