* They are giant balls of hot, glowing gas. The primary gas is hydrogen, which fuses into helium through nuclear fusion.

* They generate their own light and heat. This energy is released by the nuclear fusion process happening in their cores.

* They are held together by gravity. This force keeps the immense pressure of the fusion process contained.

* They have a lifecycle. Stars are born, evolve over millions or billions of years, and eventually die.

* They are primarily composed of hydrogen and helium. These elements make up the vast majority of a star's composition.

Let me know if you'd like to learn more about any of these characteristics!