Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density because
A)the lines are blue shifted.
B)the lines are red shifted.
C)the lines are extremely broad.
D)the lines are extremely narrow.
E)the lines are much darker than the stellar lines.

Question

Quizplus · Accepted Answer

Extremely narrow absorption lines indicate that the absorbing material is cold and of very low density. This is because the atoms or molecules can only absorb photons with specific wavelengths, resulting in narrow absorption lines. The lower the density of the material, the less likely it is that there will be collisions between particles that could broaden the absorption lines.

Absorption Lines Due to the Interstellar Medium Indicate That Some