When we see that a spectral line of a galaxy is broadened,that is,spanning a range of wavelengths,we conclude that
A)we do not have very good resolution of a star's orbital velocity.
B)there are many stars traveling at extremely high orbital velocities.
C)there are different Doppler shifts among the individual stars in the galaxy.
D)we are actually measuring the orbital velocity of a cloud of atomic gas.
E)we are actually measuring the orbital velocity of dark matter.

Question

Quizplus · Accepted Answer

The broadening of a spectral line in a galaxy is due to the different Doppler shifts of the individual stars within that galaxy. Each star moves at its own velocity relative to us, causing its spectral lines to shift by varying amounts. This collective effect results in the broadening of the spectral line when observed from Earth.

When We See That a Spectral Line of a Galaxy