We Detect Neutral Gas in the Interstellar Medium by Looking

question 29

Multiple Choice

We detect neutral gas in the interstellar medium by looking for radiation at 21 cm that arises when:

• A) an electron moves from the n = 1 to n = 2 state in a hydrogen atom
• B) an electron is ionized from a hydrogen atom
• C) carbon monoxide (CO) gas is excited by stellar radiation
• D) the spin of an electron flips and aligns with the spin of a proton in a hydrogen atom
• E) an electron combines with a proton to make a hydrogen atom

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