Quasars Emit Significant Amounts of Radiation from the Lyman-Alpha Transition

question 46

Multiple Choice

Quasars emit significant amounts of radiation from the Lyman-alpha transition. When the spectrum is observed on Earth, it is found that the Lyman-alpha line is accompanied by many absorption lines, called the Lyman-alpha forest. What is the origin of these lines? See Figure 18-5 in the text.

• A) The absorption lines are caused by the rotation of the quasar. Different parts of the quasar thus give rise to Lyman-alpha lines with different Doppler shifts.
• B) The absorption lines are the result of gravitational lensing by objects between the quasar and Earth.
• C) The emitted Lyman-alpha radiation is absorbed by many gas clouds between the quasar and Earth. The lines are receding at various velocities and thus are absorbed at different Doppler-shifted wavelengths.
• D) Because the quasar's jets are aimed at various directions, the jet plasma has Doppler shifts that are different from those of the quasar itself. The result is a variety of Lyman-alpha wavelengths in the spectrum received on Earth.

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