What is a protostar?

Stars are born in clouds of dust and gases, mainly hydrogen. More and more gas is pulled together by gravity to form a cloud. After a while the cloud begins to spin. This makes the gas atoms bump into each other at high speeds, creating a great deal of heat. As the cloud becomes hotter a nuclear reaction takes place inside, and the cloud begins to glow. This glowing cloud is called a protostar. The protostar continues to contract until it becomes a star.