Answer: Sb
Astronomer Edwin Hubble invented a morphological classification of galaxies. According to its form, galaxies fall into four major types: spiral, barred spiral, elliptical and irregular. Spiral galaxies are the ones who have a bulge at the center and contains spiral arms. The galaxies that are spiral-shaped, with a nuclear region of moderate size and moderately wound arms are classified under Hubble classification as Sb.
