A portion of a nebula that becomes denser leads to the formation of which structure as it attracts surrounding material?

• A. An accretionary disk
• B. Black hole
• C. Planetary ring
• D. Comet belt

Answer: (A)

When a region of a nebula becomes denser, gravity pulls in surrounding gas. The gas isn’t point-like; it has some angular momentum, so it can’t all fall straight inward. Instead, it spirals around the central mass and forms a rotating, flattened disk—the accretion disk. This disk acts as the channel delivering material to the growing core or protostar (or even a developing black hole) as gravity draws more matter inward. The idea is that the dense region gathers material, and the angular momentum of that material naturally creates a disk rather than a single point of infall. This makes the accretion disk the structure that forms in this scenario, rather than a planetary ring, a comet belt, or a separate black hole by itself (which could be associated with the disk, but the disk is the immediate result of the infalling gas).