Star galaxies are vast systems containing stars, stellar remnants, gas, dust, and dark matter, all bound together by gravity. They come in various shapes and sizes, from dwarf galaxies with just a few million stars to giant galaxies with trillions of stars.

Galaxies are classified based on their shapes, including spiral, elliptical, and irregular. Spiral galaxies; like the Milky Way, have a disk-like structure with spiral arms. Elliptical galaxies are more rounded and lack distinct spiral arms. Irregular galaxies have irregular shapes and often result from gravitational interactions with other galaxies.

The study of galaxies; known as galactic astronomy, helps us understand the formation; evolution; and dynamics of these cosmic structures.