Protoplanetary disks form as nebulae combine and flatten, with material orbiting around which central object?

• A. Proto-Sun
• B. Earth
• C. Neutron star
• D. Comet

Answer: (A)

Protoplanetary disks form around a young star because gravity pulls gas inward while angular momentum must be conserved. The infalling material spins up and spreads into a flat, rotating disk that surrounds the growing protostar. In our solar system, that central object is the proto-Sun—the forming Sun around which the disk develops and later gives rise to planets. The other options don’t fit this scenario: Earth is a planet, not the central mass during disk formation; a neutron star is a collapsed stellar remnant, not the typical site of planet-forming disks; and a comet is a small body within the disk, not the central object itself.