Galaxy classifications and structural characteristics

Galaxies are massive collections of billions of stars held together by gravitational forces. They are generally categorized into three main types: spiral, barred, and irregular galaxies.

Spiral galaxies, including the Milky Way and the Andromeda Galaxy, feature classic spiral structures formed by rotation and internal gravitational forces. While the Milky Way's structure cannot be photographed from the outside, the CSIRO Parkes Radio Telescope has been used to observe its underlying structure.

Barred galaxies, such as NGC 1300, are characterized by a bright central bar of stars with arms spiraling out from each end. Irregular galaxies, such as the Large Magellanic Cloud, the Small Magellanic Cloud, and the colliding Antennae Galaxies, lack a distinctive or easily categorized structure.