Spiral structure can be triggered in a disk galaxy by
A) a close encounter with a passing galaxy.
B) an orbiting dwarf galaxy.
C) an off-center burst of star formation in the disk.
D) All of the above

Question

Quizplus · Accepted Answer

Spiral structure in a disk galaxy can be triggered by all of the above factors. A close encounter with a passing galaxy can cause gravitational disturbances that compress gas and trigger star formation, leading to the formation of spiral arms. An orbiting dwarf galaxy can also create similar gravitational disturbances. An off-center burst of star formation can produce density waves that propagate through the disk and trigger spiral arms.

Spiral Structure Can Be Triggered in a Disk Galaxy by