Galaxies consist of stars, planets, and vast clouds of gas and dust, all bound together by gravity. The largest contain trillions of stars and can be more than a million light-years across. The smallest can contain a few thousand stars and span just a few hundred light-years.
Most galaxies are between 10 billion and 13.6 billion years old. Some are almost as old as the universe itself, which formed around 13.8 billion years ag
