What is a stellar nursery primarily composed of?

A stellar nursery, also known as a molecular cloud or star-forming region, is primarily composed of hydrogen gas. These regions are vast clouds of gas and dust where conditions are cold and dense enough to promote the gravitational collapse of material, leading to the formation of new stars. Hydrogen is the most abundant element in the universe, making up about 75% of its elemental mass, and it serves as the primary fuel for the nuclear fusion processes that eventually occur in stars.

In addition to hydrogen, stellar nurseries contain other elements and compounds, including helium and trace amounts of heavier elements, but these are present in much smaller quantities. The presence of hydrogen gas allows for the formation of molecules like H2 (molecular hydrogen), which are crucial for the cooling of the gas cloud, enabling the star formation process to begin.

Thus, hydrogen gas is the fundamental component that defines a stellar nursery, setting the stage for the birth of stars and the complex processes that follow in galactic evolution.