What are hot clouds of gaseous elements and compounds that act as nurseries for stars

Interstellar gas clouds are common in many galaxy, like the Orion nebulae which many young stars are being born. A typical nebula is many light years in diameter and contains enough material mass to make several thousand stars the size of our sun. The majority of the gas in nebulae consist of molecules of hydrogen and helium-but most nebulae also contain atoms of other elements. All known element in our periodic table is also being made inside this crucible of this immense hot gas. The source of the organic molecules is still a mystery. Irregularities in the density of the gas causes a net gravitational force that pull the gas molecules close together.