The shape of our galaxy, the Milky Way, is a spiral. A bulge of older stars exists at the center of the spiral and the arms of the spiral contain newer stars. A black hole possibly exists in the very center of the Milky Way.
Gravity holds the Milky Way galaxy together. Its radius measures about 50,000 light years, and the sun orbits the center of the galaxy between the Perseus and Sagittarius arms of the Milky Way.
Spiral galaxies are the most common type of galaxy; in fact 77 percent of known galaxies are of the spiral type. The arms of spiral galaxies, the birthplace of new stars, contain large amounts of dust and gas.