Facts about the The Galaxy, Just as stars are born in groups or clusters, so do galaxies also exist in groups. Our galaxy belongs to a cluster of approximately 32 galaxies called the Local Group. Most of the galaxies in the Local Group are small and faint and would be invisible to us if they were much farther away. Beyond the edge of the Local Group, astronomers have discovered thousands of other groups of galaxies in the universe. There groups in turn seem to form looser groups in space, known as super clusters.
Galaxies are put into classes based on their shape Irregular galaxies (class ir) are usually smaller than the Milky Way. The gravity of larger galaxies pulls these types out of shape.
Elliptical galaxies seem to have no nebulae, which mean they cannot form any stars. They are on a scale from E0 (almost spherical) to E7 (very elongated). The largest known galaxies are giant ellipticals, but dwarf ellipticals are also very common.
Ordinary spiral galaxies are classed from Sa (very tight arms) to Sc (very loose arms). Another type, S0, has a very large nucleus, or center, which is more like and elliptical galaxy. Until recently, the Milky Way was thought to be an Sb or a Sc type.
Barred spiral galaxies classed from SBa (tight arms) to SBc (loose arms) have a center with a short bar of stars across them. The spiral arms begin at the ends of this bar. Astronomers have in recent times discovered that there is such a bar in our on galaxy, the Milky Way.