How Are Rotation Curves of Spiral Galaxies Determined Beyond Radii

question 63

Multiple Choice

How are rotation curves of spiral galaxies determined beyond radii where starlight can be detected?

• A)by extrapolation
• B)through observations of the 21 cm line of atomic hydrogen
• C)through observations of spectral lines of dark matter
• D)by watching the galaxies rotate over a period of years
• E)by measuring the broadening of absorption lines

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