Galaxien, or galaxies in English, are vast systems that contain stars, planets, gas, dust, and dark matter, all bound together by gravity. They can vary in size and shape, with the most common types being spiral, elliptical, and irregular. Our own galaxy, the Milky Way, is a spiral galaxy that houses billions of stars. Galaxien can range from a few billion stars to trillions, and they often exist in groups known as galaxy clusters. The study of galaxies helps astronomers understand the universe's structure and evolution, including the formation of stars and the behavior of dark matter.