The Milky Way contains several thousand giant molecular clouds. Describe a giant molecular cloud and its role in star formation

A Giant Molecular Cloud (GMC) is a massive and dense cloud of gas in space. These clouds are primarily made of molecular hydrogen (H2), the simplest and most abundant molecule in the universe. Besides hydrogen, GMCs also contain other molecules like carbon monoxide (CO).

They are called 'giant' because they can be extremely large, with masses ranging from thousands to millions of times the mass of our Sun, and spanning tens to hundreds of light-years in diameter. These clouds are the coldest type of molecular clouds, with typical temperatures between 10 to 20 Kelvin (-263°C to -253°C). Due to these low temperatures and high densities, they are the perfect sites for star formation.

Star formation is a complex process that begins in Giant Molecular Clouds (GMCs). These cold and dense regions provide the ideal conditions for the birth of stars.

Inside a GMC, small regions can collapse under their own gravity. Initially, the gas and dust in the cloud clump together due to slight disturbances like shock waves from nearby supernovae. As these clumps gather more material, they become denser and warmer. Eventually, they reach a point where nuclear fusion can ignite in their cores. This marks the birth of a new star.

• GMCs provide the raw material needed for star formation.
• Gravitational forces cause the dense regions to collapse.
• Heat and pressure increase until nuclear fusion begins.

Star formation is not an isolated event; it often triggers the formation of new stars in neighboring regions, leading to star clusters.

Gravitational collapse is a fundamental process in star formation. It occurs when a region within a Giant Molecular Cloud becomes unstable and begins to contract under its own gravity.

Several factors can cause this collapse, such as shock waves from nearby supernovae, collisions between clouds, or even the rotational inertia of the cloud itself. As the region collapses, it forms a protostar at the center. The material falling inward increases the temperature and pressure until the conditions are ripe for nuclear fusion.

• Gravity pulls gas and dust inward.
• Shock waves or cloud collisions can trigger collapse.
• Collapsing material forms a protostar.

Without gravitational collapse, the dense regions within GMCs couldn't become hot and dense enough to start nuclear fusion.

Nuclear fusion is the process that powers stars, including our Sun. It occurs when the dense core of a collapsing region within a GMC becomes hot and pressurized enough for hydrogen nuclei to merge, forming helium and releasing tremendous amounts of energy.

This energy not only provides the light and heat we receive from stars but also creates a balance against the gravitational forces trying to compress the star further.

• Fusion ignites when temperatures reach millions of degrees.
• Hydrogen nuclei combine to form helium.
• The process releases vast amounts of energy.

The energy from nuclear fusion is what makes a protostar shine brightly and ultimately evolve into a stable star.