Question: what are characteristics that all galaxies share?
Answer: A galaxy contains stars, gas, and dust. In a spiral galaxy like the Milky Way, the stars, gas, and dust are organized into a bulge, a halo, and a disk containing spiral arms. Elliptical galaxies have a bulge shape and a halo, but do not have a disk. Bulge—A round structure made up primarily of old stars, gas, and dust.