Stars are born in vast clouds of gas and dust called nebulae. Nebulae are made up of hydrogen and helium, the two lightest and most abundant elements in the universe. When a nebula becomes dense enough, it will start to collapse under its own gravity. As the nebula collapses, it will begin to rotate faster and faster. This rotation causes the nebula to form a disk. The center of the disk will become very hot and dense, and this is where a star will eventually form.