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

Question

Quizplus · Accepted Answer

Rotation curves of spiral galaxies beyond radii where starlight can be detected can be determined through observations of the 21 cm line of atomic hydrogen. This technique is used to map the distribution of neutral hydrogen gas in galaxies and indirectly trace the mass distribution, allowing for the determination of rotation curves.

How Are Rotation Curves of Spiral Galaxies Determined Beyond Radii