Quasars are estimated to be only one or two light-years in diameter. This is surprising because they emit 10 to 1,000 times more electromagnetic radiation than a normal galaxy which can have a diameter of greater than 100,000 light years. Galaxy M51 Galaxies are enormous cluster of stars. Small galaxies may contain fewer than a million stars while very large galaxies may contain more than one trillion stars. Galaxies can be up to 100,000 light-years in diameter.
Elliptical galaxies show very little structure and are flat to spherical in shape.
Spiral galaxies are flat and generally have a bright nucleus, and arms that come out of the nucleus and form a giant pinwheel shape. Barred spiral galaxies are also flat and have arms that extend sideways in a short straight line before curving into a spiral shape. Irregular galaxies are usually small and have no particular shape. The Milky Way is our Galaxy. Some astronomers estimate that the Milky Way has more than 100 billion stars.