The Tully-Fisher Relationship Relies on Broadening of the 21-Cm Radio

question 187

Multiple Choice

The Tully-Fisher relationship relies on broadening of the 21-cm radio line in distant spiral galaxies. What causes this broadening?

• A) thermal motion of the gases in the galaxy
• B) random motions of the stars in the galaxy
• C) rotation of the galaxy
• D) general expansion of the universe (Hubble flow)

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