Galaxy

The galaxies are clusters of billions of stars. Stars, gas, and interstellar dust orbit the center of the galaxy due to the gravitational pull of all other stars. New generations of stars are born from gas that condenses into regions called giant molecular clouds, and stars sometimes form star clusters. When a star reaches the end of its evolution, it can return a lot of gas to the interstellar medium that will be the source for a new generation of stars. We can imagine galaxies as systems that transform gas into stars and stars turn back to gas.