Final answer:
Interstellar gas clouds can collapse under their own gravity to become denser and form new stars. This process is characterized by the gravitational contraction of the cloud, the consequent increase in kinetic energy turning into heat, and eventually the temperatures becoming high enough for nuclear fusion to occur.
Step-by-step explanation:
Interstellar gas clouds may collapse to form stars if they become denser due to gravity. When a gas cloud in space collapses, it does so because of gravitational attraction, which causes the particles within the cloud to move towards its center, thus converting gravitational potential energy into kinetic energy. This increase in kinetic energy leads to the formation of a hot ball of gas through particle collisions - the beginning stages of a star. The process continues with the proto-star contracting further and additional gravitational potential energy converting into thermal energy, thereby increasing its temperature substantially.
However, the interstellar medium is dynamic, with new gas being constantly added from intergalactic space. In regions where gravity causes the gas to collect, like in giant molecular clouds, the gas can collapse to form new stars. It is a process where matter from the clouds becomes locked into stars, which, after their life cycles, may release some matter back into space, contributing to the cycle of star birth and death.
All the heavier elements beyond hydrogen are formed within stars in highly concentrated and high-temperature conditions. It is during the contraction and compression of gas, predominantly hydrogen, caused by gravity, that temperatures reach the levels necessary for nuclear fusion. This process, known as 'hydrogen burning,' is responsible for converting hydrogen into helium and releasing an immense amount of energy.