Supermassive black holes erupt in ____.
a. any type of galaxy, and at random times
b. elliptical galaxies only, when the last of their gas and dust is consumed
c. galaxies that have been part of a collision or merger
d. spiral galaxies only, during a burst of star formation
e. irregular galaxies
Question 2
Absorption lines are produced by ____.
a. atoms that become ionized
b. electrons that transfer from a high energy level to a low energy level
c. electrons that transfer from a low energy level to a high energy level
d. the intensity of agitation of atoms in a hot gas
e. the motion of an object toward or away from the observer