Question

what is a stable, tightly bound cluster of stars held together by gravity? * halo dwarf galaxies protoplanets globular clusters

Explanation:

A halo is a region around a galaxy. Dwarf galaxies are small galaxies. Protoplanets are bodies in the process of forming planets. A globular cluster is defined as a stable, tightly - bound cluster of stars held together by gravity.

Answer:

D. Globular clusters